High accelerating gradients are very attractive for future machines, and, in particular, for high current heavy ion linac projects like the "Inertial Fusion Driver". In order to explore the maximum field achievable in an Interdigital-H type structure, an experiment has been carried out at CERN on the Lead Ion Linac (Linac3). After the 1997 run, the RF amplifiers were rearranged in order to allow the feeding of the IH Tank number 2 (1.55 m long, 28 gaps, frequency of 202.56 MHz) with up to 2 MW pulsed RF power. After two weeks of conditioning at pulse lengths variable between 200 microseconds and 1 millisecond with a constant pulse repetition rate of 0.8 Hz, the maximum effective acceleration gradient achieved was 10.5 MV/m. This corresponds to a local field maximum of 5 times the Kilpatrick limit, and to fields in excess of 3.5 times Kilpatrick on large portions of the drift tube surfaces. This paper reports the conditioning procedure applied, the measurements of field emission current at different voltages and pulse lengths, the determination of the surface field enhancement factor as well as the calculation of the electric field distribution for the gap with the highest surface fields.

TH4005
Design of the KOMAC H⁺/H^- RFQ Linac

J.M. HAN, Y.S. CHO, B.H. CHOI, KAERI; S.H. JIN, I.S. KO, PAL-POSTECH; B.S. KANG, B.S. HAN, SHIC

A 350 MHz, cw Radio-Frequency Quadrupole (RFQ) will be built to produce 20 mA of H⁺/H^- beam at 3 MeV for the Korea Multipurpose Accelerator Complex (KOMAC) projects 1GeV linac. The beam dynamics and the engineering design of the Low Energy Beam Transport (LEBT) and RFQ are described. The detail design of a vacuum pumping system for the KOMAC RFQ is presented.

TH4006
RFQ-Accelerators for Radioactive Ion-Beams

T. SIEBER, O. KESTER, D. HABS, LMU Muenchen; A. SCHEMPP, IAP-Univ. of Frankfurt

For the REX-ISOLDE LINAC at CERN a 4-rod-RFQ is built up and tested at Munich. This RFQ has a length of 3 m and will accelerate neutron-rich ions from 5 keV/u to 300 keV/u. It operates at a resonant-frequency of 101.28 MHz with a duty-cycle of 10%. The transmission has been calculated with PARMTEQ to 98%. In the poster the mechanical characteristics of the RFQ and the results of the rf-measurements will be presented.

Furthermore we want to show, that - alternative to the well tested and reliable 4-rod-RFQ-structures - IH-type RFQ's like the new GSI high-current-injector-RFQ [1] (resonant-frequency: 36 MHz) could also operate at frequencies around 100 MHz. For the planned fission fragment accelerator of the Munich high-flux reactor, investigations are under progress on such an IH-RFQ. Advantages of this structure might be a high efficiency, indirect electrode-cooling and the possibility to use finger drift-tubes in addition.

The IH-RFQ will operate at 101 MHz and accelerate ions with A/q=6.3 to about 300 keV/u. The particle dynamics will be similar to the REX-RFQ. MAFIA-calculations for a 0.75 m model and for the 3 m power-resonator will be presented together with first measurements on the model.

Classification Category: A02

TH4007

Contribution withdrawn.

TH4008
Recent Developments of the Folded-Coaxial RFQ for the RIKEN Heavy Ion Linac

O. KAMIGAITO, A. GOTO, Y. MIYAZAWA, T. CHIBA, M. HEMMI, M. KASE, S. KOHARA, E. IKEZAWA, T. NAKAGAWA, Y. YANO, RIKEN

In August 1996, a new injector system for the RIKEN heavy ion linac (RILAC) was installed, which consists of an 18-GHz ECR ion source and a variable-frequency RFQ based on a folded-coaxial resonator. The beam intensities have remarkably increased after the installation. For example, the intensity of Xe beam has increased by about two orders of magnitude compared with those using the Cockcroft-Walton injector. The maximum power of the beam extracted from the RILAC and that from the ring cyclotron have reached 560 W and 2 kW, respectively. In order to achieve these results, the maximum extraction voltage of the ECR ion source was raised from 10 kV to 20 kV in August 1997. The RFQ vanes were replaced correspondingly at the same time. Another important result we have obtained is that the transmission efficiency of the RILAC has exceeded 80 % by use of the pre-buncher placed before the RFQ. Operational experiences of the RFQ as well as recent developments are described in this paper.

TH4009
First Beam Test with the ISAC RFQ

R.E. LAXDAL, R. BAARTMAN, G. DUTTO, K. FONG, K. JAYAMANNA, M. MACDONALD, A. MITRA, R. POIRIER, W. RAWNSLEY, L. ROOT, B. UZAT, J. WELZ, TRIUMF

The ISAC RFQ is a 35 MHz, split-ring, four vane structure designed to accelerate ions of A/q30 from 2keV/u to 150keV/u in cw mode. When completed the RFQ will comprise 19 modules, each composed of one split-ring connected to 40cm of electrodes in quadrature for a total length of about 8m. The first 7-ring portion of the RFQ is scheduled for testing with beam in an interim configuration in early summer of this year. A copper wall internal to the RFQ tank isolates the rf power to the electrode region. Electrostatic quadrupoles are installed in the remainder of the tank to transport the beam to a downstream diagnostic station. An injector composed of a 2.45GHz ion source in a CUSP geometry and an electrostatic LEBT and matching section delivers stable light ions to the RFQ. The beam is pre-bunched with an 11.7MHz pseudo saw-tooth waveform across a single gap to satisfy an experimental requirement for 90ns between beam bursts. The diagnostic station consists of Faraday cups, a fast Faraday cup, an emittance rig, and an analyzing magnet. The complete test set-up will be described and the results of commissioning the injector and testing the RFQ will be summarized.

TH4010  (oral poster TH3001)
Status of the ISAC Accelerator for Radioactive Beams

R.E. LAXDAL, R. BAARTMAN, P. BRICAULT, G. DUTTO, R. POIRIER, P. SCHMOR, TRIUMF

The ISAC radioactive beam facility under construction at TRIUMF includes a 500MeV proton beam (I100microA) impinging on a thick target, an on-line source, a mass-separator, an accelerator complex, and experimental areas. The accelerator chain includes a 35MHz RF Quadrupole (RFQ) to accelerate beams of A/q30 from 2keV/u to 150keV/u and a post-stripper, 105MHz variable energy drift tube linac (DTL) to accelerate ions of 3A/q6 to a final energy from 0.15 to 1.5MeV/u. The accelerators have several noteworthy features. Both linacs are required to operate cw to preserve beam intensity. The RFQ, a four vane split-ring structure, has no bunching section; instead the beam is pre-bunched at 11.7MHz with a single-gap, pseudo saw-tooth buncher. The variable energy DTL is based on a unique separated function approach with five independent interdigital H-mode (IH) structures providing the accleration and quadrupole triplets and three-gap bunching cavities between tanks providing transverse and longitduinal focussing respectively. The present status of the accelerator complex will be reported. In particular, first beam tests with the RFQ and power tests of both the first DTL IH tank and DTL buncher are scheduled for this summer.

TH4011
Operation of the VE-RFQ Injector for the ISL Cyclotron*

O. ENGELS, A. SCHEMPP, F. HÖLLERING, IAP-Univ. of Frankfurt; J. HÄUSER, NTG, Neue Technologien; H. HOMEYER, W. PELZER, A. DENKERT, Hahn-Meitner-Institut

The VE-RFQ-injector for the cyclotron at HMI in Berlin is now in operation. The ECR-source together with the RFQs supply heavy ion beams with 90 - 360 keV/u for q/A > 0.15, matched to the isochronous cyclotron. Properties of the new injector and results of rf-measurements, high power tests and beam measurements are presented.

*Work supported by the BMBF.

TH4012
Design of a High Current RFQ Injector with High Duty Factor*

H. VORMANN, A. SCHEMPP, U. BESSLER, IAP-Univ. of Frankfurt; C. W. PLANNER, A. LETCHFORD, RAL

An RFQ injector with a duty factor up to 10% is planned for the spallation source ISIS at Rutherford Appleton Laboratory (RAL). The accelerator will be a Four Rod RFQ with directly cooled electrodes, operating at 202 MHz. The RFQ will provide a H^- beam current up to 50 mA with an output energy of 665 keV (input energy 50 keV). The beam dynamics, rf and mechanical designs are presented.

* Work supported by the BMBF.

Classification Category: A02

TH4013

Contribution withdrawn.

TH4014
Proposal to use PIVAIR as a 30 GHz High-Power Generator

J. L. RULLIER, J. GARDELLE, T. LEFEVRE, CEA/Cesta; J.T. DONOHUE, CENBG

The Two-Beam Accelerator (TBA) is under active study both at Lawrence Berkeley National Laboratory (LBNL) and at CERN. In the TBA an extremely intense low-energy electron beam is bunched at the desired operating frequency, and upon passing through resonant cavities generates high-gradient radio-frequency (RF) power for accelerating the main beam. Among the different approaches to the production of a suitable drive-beam, the use of a free-electron laser has been proposed. Recently at CEA-CESTA, encouraging results in this direction have been obtained. To extend this work, we propose the use of the induction accelerator "PIVAIR" at CESTA (7 MV, 4 kA) as a test stand for high power RF structure experiments at 30 GHz. Our research program for PIVAIR includes:

• Production of a drive beam current profile designed to compensate beam loading,
  
• High power tests of a CLIC Transfer Structure,
  
• Tests of the 30 GHz RK-CLIC components.

TH4015
First Order Design Study of an Accelerator Beamline for the PEARL FEL

M. C. LAMPEL, G. H. Gillespie Associates, Inc.; J. M. J. MADEY, Duke University; R. J. BURKE, Arcata Systems

The Pan-Oceanic Environmental and Atmospheric Research Laboratory (PEARL) consortium has proposed the deployment of a ship-based FEL facility for advanced atmospheric and environmental research and to develop remote sensor technology. The FEL is intended to have an optical output from approximately 20 microns down to 1/3 micron, with up to 1 kW average power at longer wavelengths. The accelerator will operate over a wide range of beam currents and energies to meet these goals. The proposed shipboard FEL must meet design constraints in compactness and efficiency. The accelerator beamline, upstream of the FEL resonator, includes a 4.5 MeV rf gun, pulse length compression chicane, and four 1.26 meter long travelling wave (TW) accelerator sections. First order focussing along the beamline is provided by quadrupole magnets. First order beam dynamics for this beamline are studied using TRACE 3-D with a self-consistent TW accelerator model incorporated into it. Parametric studies of beamloading effects on accelerator efficiency and beam transport are performed. Beamline layouts, taking into account the physical dimensions and operating parameters of the equipment will be studied to determine the baseline beamline design for further, higher order simulations, on the way towards an optimized design.

TH4016
First Lasing of the JAERI FEL Driven by the Superconducting RF Linac

E.J. MINEHARA, M. SUGIMOTO, M. SAWAMURA, R. NAGAI, N. KIKUZAWA, N. NISHIMORI, JAERI

First and stable laser oscillation has been obtained at a wavelength of 24 micrometer using the JAERI (Japan Atomic Energy Research Institute, Tokai) superconducting rf linac based FEL driver. Electron beam energy and resolution are 15.8MeV, and 0.6% respectively, the beam current and pulse width a few mA and 0.8ms or less, respectively. The optical resonator with a 52 period hybrid planer undulator (K=0.7) is 1.7m long and uses Au coated Cu mirrors of 120mm diameter. The optical axes and distance of the mirrors is adjusted by remotely controlled actuators in order to coincide with the electron beam and micro pulse repetition rate, respectively, before the oscillation. The power is scattered at least around 8 orders of the magnitude higher than that of the spontaneous emission. During the first successfull operation, the highest FEL power was measured to be several tens watts in average. The FWHM of the FEL spectrum is less than 0.6 micrometer, which corresponds to 2.5% of the wavelength. The tuning range of the cavity is about 15 micrometer.

TH4017
Recent Performance of the JAERI Superconducting Linac for FEL

M. SAWAMURA, R. NAGAI, N. KIKUZAWA, N. NISHIMORI, E.J. MINEHARA, JAERI

Far-infrared FEL oscillation using the superconducting linac has succeeded in JAERI. The linac consists of a 250kV electron gun, a subharmonic normal-conducting buncher (SHB) of 83.3MHz, two single-cell and two 5-cell superconducting cavities of 499.8MHz. The gun was typically operated around 200 kV to reduce space charge effects. The combination of the SHB and two single-cell cavities enabled high current beam of more than ten amperes by utilizing a thermionic cathode and a grid pulsing. The two single-cell cavities were powerful enough to compress high current beam and to reduce the space charge effects. Calculations utilizing the modified PARMELA code showed that the electron bunch of 3 ns from the electron gun was finally compressed to be 20-35 ps with the energy resolution of 2.3-3.1 % in FWHM after the two single-cell cavities. The major part of the transverse emittance hardly increased. FWHM bunch length and energy resolution were measured to be 22ps and 3% or less, respectively. The measured results agreed with the calculated. This showed the validity of the linac design for the FEL.

TH4018
Electron Beam Charge State Amplifier (EBQA): Concept and Simulations*

J. C. DOOLING, J. A. NOLEN, ANL

A concept referred to as an EBQA is presented for stripping low energy radioactive ions from 1+ to higher charge states. In an EBQA, continuous beams of 1+ radioactive ions extracted from standard Isotope-Separator-Online (ISOL) sources are passed through a high-density electron beam which is confined by a solenoidal magnetic field in a geometry similar to an Electron Beam Ion Source. An EBQA is potentially useful to increase the charge states of ions prior to post acceleration at ISOL radioactive beam facilities. The efficiency of stripping ions from q=1+ to 2+ is evaluated as a function of electron beam radius at constant current with solenoid field, injected ion energy, and ion beam emittance used as parameters. With a 5 keV, 1 A electron beam, stripping efficiencies of 38% are calculated for 0.1 keV, mass 132 ions with a single pass through an 8 Tesla by 1 m long solenoid. Multi-pass configurations to achieve 3+ or 4+ charge states are also conceivable. The calculated efficiencies depend inversely on the initial ion beam emittances. Hence, the use of a helium-buffer-gas, ion-guide stage to improve the brightness of the 1+ beams would enhance the performance of the EBQA. Examples of how an EBQA could be used at the front end of a continuous-wave radioactive beam post accelerator will also be presented.

*This work is supported by the U. S. Department of Energy under contract W-31-109-ENG-38.

TH4019

Contribution withdrawn.

TH4020
Long Range Plan Proposal for an Extension to ISAC

R. BAARTMAN, R. LAXDAL, L. ROOT, TRIUMF

A radioactive ion beam facility, ISAC, is presently under construction at TRIUMF. The post-accelerator comprises a 35 MHz RFQ to accelerate ions of A/q 30 from 2 keV/u to 150 keV/u and a post-stripper room temperature 105 MHz DTL to accelerate ions of 3 A/q 6 to a final energy fully variable up to 1.5 MeV/u. Both linacs are required to operate in cw mode. For the next five year plan, it is intended to increase the final energy above the Coulomb barrier (roughly 6.5 MeV/u) and broaden the mass range up to roughly A = 150. The ISAC-2 proposal will utilize the existing RFQ. Masses higher than 30 will require ECR ion sources and/or charge boosters. To optimize the total accelerating voltage while utilizing a single stripping stage requires that the stripping energy be increased from 150 keV/u to 400 keV/u. A 105 MHz room temperature IH-DTL would supply the required 7.5 MV from RFQ to stripper. The post-stripper linac is required to accelerate ions of A/q 7 from 0.4 to 6.5 MeV/u (42.7 MV). Both a room temperature and a superconducting DTL structure have been considered. The room temperature approach would consist of long IH tanks (GSI model). The superconducting structure would consist of short (2 to 4 cell) independently-phased cavities (ATLAS model). In this paper we compare the various ISAC-2 options and present first order linac designs, cost estimates and staging scenarios.

TH4021
Status of the REX-ISOLDE LINAC*

O. KESTER, D. HABS, T. SIEBER, R. RAO, K. RUDOLPH, A. KOLBE, P. THIROLF, LMU München; R. VON HAHN, H. PODLECH, R. REPNOW, D. SCHWALM, MPI für Kernphysik; A. SCHEMPP, K.-U. KÜHNEL, C. WELSCH, IAP-Univ. of Frankfurt; U. RATSINGER, GSI Darmstadt; and the REX-ISOLDE collaboration

The Radioactive beam Experiment (REX-ISOLDE) [1] a pilot experiment testing a new concept of post acceleration of radioactive ions at ISOLDE/CERN is under progress. Radioactive singly charged ions delivered by the on-line mass separator ISOLDE are accumulated in a Penning trap, then charge breeded to A/q < 4.5 in an electron beam ion source (EBIS) and finally accelerated in a LINAC from 5 keV/u to the final energy between 0.8 and 2.2 MeV/u. The resonant structures of the LINAC consist of a Radio Frequency Quadrupole (RFQ) accelerator, an interdigital H-type structure (IH) and three seven gap resonators, which allow a variation of the final beam energy. New beam line calculations of the mass separator and the matching section between RFQ and IH-structure have been carried out. First low level measurements have been done and power tests of the RFQ will be performed at the Munich Tandem Laboratory in the middle of 1998. A test beam line including a duoplasmatron ion source, an electrostatic quadrupole lens system and a diagnostic box is being built up. The vacuum tank of the IH-structure is in production and will be copper plated in June and July. First low level measurements in comparison with model measurements [2] and MAFIA calculations will be presented. The production of the resonant structures and of the first tanks of the seven gap resonators is almost completed. First low level and power measurements are foreseen in the middle of the year and will be shown.

*Work supported by BMBF FKZ 06 LM 868 I (2).

Classification Category: A06

TH4022
Relativistic-Klystron Two-Beam Accelerator as a Power Source for Future Linear Colliders*

G. A. WESTENSKOW, T. L. HOUCK, LLNL; D. E. ANDERSON, S. EYLON, E. HENESTROZA, S.M. LIDIA, D. L. VANECEK, S. S. YU, LBNL

The technical challenge for making two-beam accelerators into realizable power sources for high-energy colliders lies in the creation of the drive beam and in its propagation over long distances through multiple extraction sections. This year we have been constructing a 1.2-kA, 1-MeV, induction gun for a prototype relativistic klystron two-beam accelerator (RK-TBA). The electron source will be a 3.5"-diameter, thermionic, flat-surface cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 150-ns flat top (1% energy variation), and a normalized edge emittance of less than 200 pi-mm-mr. The prototype accelerator will be used to study physics, engineering, and costing issues involved in the application of the RK-TBA concept to linear colliders. We have also been studying optimization parameters, such as frequency, for the application of the RK-TBA concept to multi-TeV linear colliders. As an rf power source the RK-TBA scales favorably up to frequencies around 35 GHz. An overview of this work with details of the design and performance of the prototype injector, beam line, and diagnostics will be presented.

*The work was performed under the auspices of the U.S. Department of Energy by LLNL under contract W-7405-ENG-48, and by LBNL under contract AC03-76SF00098.

TH4023
Achromat with Linear Space Charge for Bunched Beams*

D. RAPARIA, J. G. ALESSI, Y. Y. LEE, W. T. WENG, BNL

The standard definition for an achromat is a transport line having zero values for the spatial disperson (R16) and the angular dispersion (R26). In presence of linear space charge this definition of achromaticity does not hold. The linear space charge provides coupling between (a) bunch spatial width and bunch length (R15) and (b) bunch angular width and bunch length (R25). Therefore, achromaticity should be redefined as a line having zero values of the spatial disperson (R16), the angular dispersion (R26), and matix elements R15 & R25. These additional conditions (R15=R25=0) can be achieved, for example, with two small RF cavities, to cancel space charge effects. An example of the application of this technique to the Spallation Neutron Source (SNS) high energy beam transport line will be presented.

* Work performed under the auspices of the U. S. Department of Energy.

TH4024
A Possible Particle-Core Approach to Mismatched Beams in a Periodic Focusing Channel

M. IKEGAMI, M. MIZUMOTO, JAERI

A method is derived for applying the particle-core analysis to mismatched beams in a periodic focusing channel in cases where the core oscillation is stable. By carefully choosing the parameters to yield a favorable core frequency, a Poincare surface of section plot is obtained. The plots for a periodic solenoid channel exhibit a striking resemblance with the continuous focusing case, while those for a FODO channel exhibit a strong chaosity which is not seen in the corresponding continuous focusing situation. It suggests that the strong modulation of the core oscillation due to an alternating-gradient focusing field affects test particle stability. Some typical numerical results and a way to find adequate parameters are presented.

TH4025
Halo Formation by Mismatch for High Intensity Bunched Beams

M. PABST, K. BONGARDT, FZJ; A. LETCHFORD, RAL

TH4026
Self-consistent 3D Simulations of Longitudinal Halo in RF-linacs

J. J. BARNARD, S. M. LUND, LLNL; R. D. RYNE, LANL

In order to prevent activation of the beam pipe walls and components of a high power ion accelerator, beam loss must be minimized. Here we present self-consistent, 3D particle-in-cell simulations of longitudinally mismatched beams, including the effects of rf non-linearities, using parameters based on the Accelerator Production of Tritium linac design. In particular, we explore the evolution of the longitudinal halo distribution, i.e. the distribution of particles in longitudinal phase space with oscillation amplitudes significantly larger than amplitudes of particles in the main body or "core" of the beam. When a particle reaches a sufficiently large amplitude longitudinally, it can be lost from from the rf bucket, and consequently loses synchronisim with the rf wave. Such particles will lose energy and so be poorly matched to the transverse focusing field and consequently can be lost transversely. We compare the present simulations, in which all particles contribute self-consistently to the self field, to predictions of a core/test particle model, in which the core distribution has uniformly distributed charge and does not evolve self-consistently. Effects of self consistent, non-linear space charge forces, non-linear rf focusing and transverse longitudinal coupling on envelope mismatch induced beam halo are explored through comparisons of both models.

TH4027
Analytic Model of Ion Emission from the Focus of an Intense Relativistic Electron Beam on a Target*

G. J. CAPORASO, LLNL

Advanced radiographic systems for stockpile stewardship require very small x-ray sources to achieve the required resolution. Focusing multi-kiloampere beams to diameters on the order of 1 mm onto a Bremsstrahlung target leads to the generation of axial electric fields on the order of several MV/cm which act to extract ions out of the surface plamsa and accelerate them upstream into the beam. These backstreaming ions act as a distributed electrostatic lens which can perturb the focus of the electron beam in a time varying manner during the pulse. An analytic model of the diode extraction is presented for a particular target geometry along with scaling laws for the perturbation of the focal spot.

*This work was performed under the auspices of the U.S. Department of Energy by the LLNL under Contract No.W-7405-Eng-48.

TH4028
Trapping Backstreaming Ions from an X-ray Converter using an Inductive Cell*

B.R. POOLE, Y.-J. CHEN, T.L. HOUCK, LLNL

High current electron beams have been used as x-ray drivers for the x-ray radiography. Typically, several thousand amperes of electron beam current at 20 MeV is focused to a millimeter spot size on a x-ray converter. Within a single pulse, the heating of the target by the electron beam will lead to rapid desorption of surface contaminants. The space charge potential of the electron beam will pull ions out of this plasma layer upstream into the beam. These backstreaming ions can act as a focusing lens which cause the beam to be overfocused at a waist upstream. The final beam spot size on the target would then be larger than intended, and the x-ray radiography resolution is reduced. We have designed a self-biased ion trap for the Experimental Test Accelerator (ETA-II) beam by using an Advanced Test Accelerator (ATA) inductive cell to prevent the backstreaming ions from moving upstream and forming a long ion focusing channel. We have studied the effects of this type of ion trap on the final focusing of the electron beam with the ETA-II beam parameters and the proposed Advanced Hydro Facility (AHF) beam parameters. Simulation results will be presented.

*This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48

TH4029
Analysis of the Frequency Dependence of the Longitudinal Coupling Impedance of a Small Hole in a Coaxial Liner

A.V. FEDOTOV, R.L. GLUCKSTERN, Univ. of Maryland

We recently developed a general analysis for a rectangular slot in the inner conductor of a coaxial liner, which allowed us to investigate the coupling impedance numerically. In the present paper we obtain analytic expressions for a small hole of arbitrary shape which includes effects of energy propagation along the inner beam pipe and/or outer coaxial pipe. This allow us to understand the structure of the impedance in the frequency region near the cutoffs of the beam pipe. We then extend our analysis to a hole in a wall of finite thickness.

TH4030

Contribution withdrawn.

TH4031
Beam Dynamics Simulations of the LANSCE Linac

F. MERRILL, L. RYBARCYK, LANL

Detailed beam dynamics calculations of the LANSCE Linac have been performed using multi-particle simulation codes. The LANSCE accelerator produces both H⁺ and H^- beam and is comprised of Cockcroft-Walton injectors, a 100MeV drift-tube linac and an 800MeV side-coupled linac. Several improvements to the simulations of H⁺ and H^- beams have recently been made. These include the use of more accurate input distributions and a better estimate of beam neutralization in the low energy beam transport. Better estimates of the accelerating fields in the drift-tube linac have also been determined through measurements and modeling. With these improvements better agreement has been achieved between the predictions and measurements of RMS beam parameters and beam losses for both beams. The details of the simulations along with predictions are presented in comparison with measurements for both H⁺ and H^- beams.

TH4032  (oral poster TH3002)

Contribution withdrawn.

TH4033
The Nonlinear Transverse RF Field Effects on the Beam Dynamics*

X. SUN, Y. LIN, Tsinghua University

The nonlinear transverse RF field effects on the low energy and emittance dominated electron beams are investigated theoretically. Without any external magnetic focusing devices and in pursuit of high shunt impedance, the nonlinear transverse RF field effects should not be neglected. The evolution of the electron beam phase space distribution is studied by taking into account the nonlinear transverse RF fields. As a result of the nonlinear transverse RF field effects, the emittance growth occurs mainly in the first cavity and is associated with the initial phases of the beam, the injection voltages of the electron gun and the accelerating gradients in the first cavity.

*Work supported by the National Science Foundation of China.

TH4034  (oral poster TH3003)
The SCHERM Space Charge Routine --- Limitations and Solutions

P. LAPOSTOLLE*, S. VALERO, N. PICHOFF, J.-M. LAGNIEL, S. NATH**, CEA/DSM/DAPNIA/SEA

The SCHERM space charge routine, reported in the 1996 linac conference, is based on representing the charge density distribution in a bunch with an Hermite series expansion. In spite of its initial promise, rigorous analyses have revealed problems which are purely of mathematical origin. Mathematical solutions of the difficulties are being tested in a continuous confined (no acceleration), as well as a periodic accelerating (6.7 MeV to 100 MeV) channel with highly tune-depressed beams. Here, we discuss the problems with series representation, solutions around it and results of the modified method applied to cases stated above.

* Consultant, SEA/CEA, Saclay
** On sabbatical from LANL, Los Alamos, NM, USA

TH4035
A Multi-Platform Graphic User Interface for the Particle Optics Code MARYLIE

G. H. GILLESPIE, B. W. HILL, M. C. LAMPEL, H. MARTONO, J. M. MOORE, K. J. RYAN, G.H. Gillespie Associates, Inc.; A. J. DRAGT, Univ. of Maryland

An advanced graphic user interface (GUI) is being developed for use with the particle optics program MARYLIE. MARYLIE is based on a Lie algebraic formulation of charged particle trajectory calculations and is particularly useful for particle tracking and the analysis of linear and nonlinear lattice properties. The GUI for MARYLIE uses the Multi-Platform Shell for Particle Accelerator Related Codes, a software framework developed specifically to support accelerator modeling and simulation. Transport element icons are selected from a palette and assembled into beamlines by graphical construction. Optical cells and lattices composed of element groups may be defined as sublines, and any element or subline can be replicated using an alias element. The icon-based beamlines generate entries for the #beam, #menu and #lines components of the MARYLIE Master Input File (MIF). Frequent computations, such as creating maps or generating particle distributions, are encapsulated into interactive GUI commands which create corresponding entries in the #menu, #lines and #labor components of the MIF. An icon-based description of procedural processes is being developed to support more complex MARYLIE analysis tasks that utilize the #lumps and #loops components. Progress on the development of this GUI for MARYLIE will be described, and the software will be demonstrated.

TH4036
X-band Klystron Output Cavity Simulation

H. TSUTSUI, S. MATSUMOTO, S. MICHIZONO, Y.H. CHIN, S. FUKUDA, KEK

Design of X-band (11.424GHz) klystrons capable of 120MW (XB72K series) is undergoing at KEK. MAGIC2D, a 2.5 dimensional particle-in-cell code, was introduced in KEK last year for the design of the next klystron XB72K-10 with a 4-cell travelling wave type output cavity. Since the coupler of the output cavity is not axisymmetrical, the structure cannot be simulated directly by 2 dimensional codes. To make 2 dimensional simulation possible, the notion of S-matrix is introduced, and is calculated using the eigenvalue solver of MAFIA codes. The saturated output powers calculated by MAGIC2D agree well with the measurements of KEK XB72K-8 and SLAC XL-4 klystrons. The design of XB72K-10 is also presented.

TH4037

Contribution withdrawn.

TH4038
Designing Double-Gap Linear Accelerators for a Wide Mass Range

W. LYSENKO, LANL

For applications like ion implantation, rf linacs using double-gap structures with external resonators can be used because they are practical at low frequencies. However, since the two gaps associated with a given resonator cannot be individually phased, it is not obvious how to design a linac that can efficiently accelerate particles having different mass/charge ratios. This paper describes the beam dynamics of double-gap rf linacs. We show how to maximize the range of mass/charge ratios that a linac design can handle, subject to the constraint that the gap voltage not exceed a given value. The range of mass/charge ratios that can be accelerated depends on the choice of synchronous phases on the two gaps. Our theory tell us how to rescale a linac tune (i.e., reset the voltages and phases) so that a new particle, having a different mass or charge, will behave similarly to the original particle.

TH4039

Contribution withdrawn.

TH4040
Physics Design of the DARHT 2nd Axis Accelerator Cell*

T.L. HOUCK, Y.-J. CHEN, C. SHANG, LLNL; L.L. REGINATO, S.S. YU, LBNL; R. BRIGGS, SAIC; D. BIRX, Science Research Laboratory

The next generation of radiographic machines based on induction accelerators require very high brightness electron beams to realize the desired x-ray spot size and intensity. This high brightness must be maintained throughout the beam transport, from source to x-ray converter target. The accelerator for the second-axis of the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility is being designed to accelerate a 4-kA, 2-5s pulse of electrons to 20 MeV. After acceleration, the 2-5s pulse will be chopped into a train of four 50-ns pulses with variable temporal spacing by rapidly deflecting the beam between a beam stop and the final transport section. The short beam pulses will be focused onto an x-ray converter target generating four radiographic pulses within the 2-5s window. Beam instability due to interaction with the accelerator cells can very adversely effect the beam brightness and radiographic pulse quality. This paper describes the various issues considered in the design of the accelerator cell with emphasis on transverse impedance and minimizing beam instabilities.

* The work was performed under the auspices of the U.S Department of Energy by LLNL under contract W-7405-ENG-48, and by LBNL under contract AC03-76SF00098.

TH4041
The Perfect Boundary Approximation Technique Facing the Big Challenge of High Precision Mode Computation

P. THOMA, CST GmbH; B. KRIETENSTEIN*, T. WEILAND, TU-Darmstadt

Computational tools for designing accelerating structures are in use since decades. While highly accurate methods exist for quasi two dimensional cavities, fully three dimensional modeling with high precision is still a "big challenge". The most widely used computer code in this area is MAFIA. While being well known for its robustness and reliability, MAFIA nevertheless suffers somewhat from a deficiency in being able to model very complicated 3D-cavities with high precision for curved boundaries. The recently developed Perfect Boundary Approximation (PBA) technique is a promising way to improve this situation drastically. The PBA-technique combines the easy-to-use Cartesian grids with a perfect approximation of boundaries. With the PBA-technique, boundaries do not need to coincide with mesh cell surfaces. Within a near-boundary cell, the exact boundary shape is taken into account resulting in a second order algorithm for arbitrarily shaped cavities. Thus the PBA-technique combines the good approximation potential of FE-methods with the robustness of FD-methods. We compare MAFIA with the PBA technique for two typical accelerator components: a 90 degree wave guide polarization rotator and a 6 cell traveling wave cavity with input/output coupler, including many small geometrical details. For such structures with many non-Cartesian metallic boundaries the PBA technique can drastically reduce the computational cost.

* Work supported in part by DESY, Hamburg.

TH4042  (oral poster TH3004)
Operation of the APS RF Gun*

J.W. LEWELLEN, A. LUMPKIN, S.V. MILTON, A. NASSIRI, S.J. PASKY, M. WHITE, ANL

The Advanced Photon Source has a thermionic-cathode rf gun system capable of providing beam to the APS linac. The gun system consists of a 1.6-cell thermionic-cathode rf gun, a fast kicker for beam current control, and an alpha magnet for bunch compression and injection into the APS linac line. This system is intended for use both as an injector for positron creation, and as a first beam source for the Low-Energy Undulator Test Line (LEUTL) project. The measured performance characteristics of the gun will be presented and compared against the measured performance of the present DC-gun injector for positron creation, and against the theoretical beam requirements for the LEUTL line.

* Work supported by US Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

TH4043
Challenges of Operating a Photocathode RF Gun Injector

X.J. WANG, M. BAZIEN, I. BEN-ZVI, R. MALONE, J. SHEEHAN, T. SRINIVASAN-RAO, M. WOODLE, V. YAKIMENKO, BNL

The 1.6 cell photocathode RF gun developed by the BNL/SLAC/UCLA collaboration has been in operation at the Brookhaven Accelerator Test Facility for more than two years. Significant progress was made in the last year to improve the stability and reliability of the photocathode RF gun injector. We will present experiment measurements of the point stability, laser energy stability and timing jitter. We have installed Magnesium cathode using frictional welding, the best quantum efficiency measured is close to 1%, and routinely operating at about 0.1%. We will also discuss the experimental results of emittance as function of charge, and coupling between the longitudinal and transverse emittance of photoelectron beam.

TH4044

Contribution withdrawn.

TH4045
Suppression of the 1-MHz Beam Current Modulation in the LEDA/CRITS Proton Source*

P. BALLEYGUIER, CEA; J. SHERMAN, T. ZAUGG, LANL

Earlier operation of a microwave proton source exhibited an approximate 1-MHz modulation in the beam current. This oscillation could cause instabilities at higher energies in the linac, as the low-level RF control for linac operation rolls off at 200 kHz. Tests on a dummy load show the modulation is created by the magnetron itself: at a typical power level required for the source operation (680W), the 1-MHz sideband level was as high as -4 dB from carrier. Since the magnetron exhibited better behavior at higher levels, an RF power attenuator is inserted to force the magnetron to run at a 50% higher power level for the same final power in the load. This attenuator is made of two antennas plunged in the waveguide and connected to dummy loads by a coaxial line. As the antennas are separated by a quarter of the guided wavelength, mismatching effects approximately cancel each other. The antenna length is experimentally adjusted to obtain the -1.8 dB attenuation required. Magnetron operation at the higher power level gives a beam current spectrum free of the 1-MHz modulation, showing the coherent beam noise is not generated by plasma chamber phenomena.

* Work supported by the U.S. Department of Energy.

TH4046
Photocathodes for the CERN CLIC Test Facility

E. CHEVALLAY, J. DURAND, S. HUTCHINS, G. SUBERLUCQ, H. TRAUTNER, CERN

Since 1993 the CLIC Test Facility (CTF) has used laser-illuminated Tellurium Alkali photocathodes as intense electron sources (up to 50 nC in 10 ps), for the Drive Beam of a two beam accelerator. These cathodes have been produced and tested in our photo-emission laboratory and transported under vacuum to the CTF. They are placed in a 3 GHz RF gun with a 100 MV/m electric field. This RF gun produces a train of 48 pulses, each of 14 nC charge and 10 ps length. The CTF Probe Beam has used air transportable Cesium Iodide + Germanium photocathodes in another RF gun, which produces a single pulse of the same duration but with only 1 nC charge. The optical damage threshold in the laser is the main limitation of energy available on the photocathode. From an operational point of view, the photocathode lifetime is the time during which the cathode is able to produce the nominal charge with the nominal laser energy. After having recalled the main characteristics of the photocathodes tested, this note describes in more detail the performance obtained in operation. The possibility of photocathode production at the RF gun in a simplified evaporation chamber will also be discussed.

TH4047

Contribution withdrawn.

TH4048
Operation of the Upgraded H^--Injection System of the Linac III at DESY

C.-M. KLEFFNER, N. HOLTKAMP, M. NAGL, H. POGGENSEE, J. PETERS, DESY

During winter 1997/98, the injection system of the H^--Linac III has been upgraded. At present two different kinds of H^--sources are operating at DESY. The new cesium-free RF ion source is planned to replace the magnetron ion source. A new MEBT (Medium Energy Beam Transport) between two distinct RFQ accelerators and the Alvarez accelerator of LINAC III was installed to match the beam of each ion source to the Alvarez acceptance. This scheme makes it possible to operate either of the ion sources with the Alvarez linac with a miniumum of effort to switch from one to the other. The design of the transport line also facilitates the development and tests of proposed ion sources for deuterium and polarized protons production. After a rapid assembly of the RFQs and ion sources as well as the new components for the MEBT, an easy operation of the LINAC could be demonstrated. The results of measurements in comparison to calculations will be presented.

TH4049
Beam Transport, Acceleration and Compression Studies in the Fermilab High-Brightness Photoinjector

J.-P. CARNEIRO, R.A. CARRIGAN, M.S. CHAMPION, A. CIANCHI, E.R. COLBY, P.L. COLESTOCK, H.T. EDWARDS, M.J. FITCH, J.D. FUERST, W.H. HARTUNG, M. KUCHNIR, K.P. KOEPKE, L.K. SPENTZOURIS, FNAL; A.R. FRY, A.C. MELISSINOS, B.D. TAYLOR, Univ. of Rochester; P. MICHELATO, D. SERTORE, C. PAGANI, INFN-Milano-LASA; J.B. ROSENZWEIG, UCLA

Efforts are underway to produce a pulse train of up to 800 electron bunches at the Fermilab Photoinjector, each with 8 nC of charge and a 3.5 ps rms bunch length. The facility consists of a high quantum efficiency photocathode in a normal conducting rf gun (1.3 GHz), a nine-cell superconducting acceleration cavity and a magnetic bunch compressor. An initial testing phase has been completed in which the rf gun and associated electron beam were studied in detail. Installation of the 9-cell cavity and bunch compressor is in progress. Once operational, the facility will be used to study beam transport through the cavity and the physics of compression at these high brightness levels. In the long term, the facility will be used to explore a number of new acceleration schemes and to provide an R&D tool for a variety of new concepts relevant to high-energy, high-intensity machines. Details of the commissioning will be presented, and plans for future studies will be discussed.

TH4050

Contribution withdrawn.

TH4051  (oral poster TH3005)
TPS Analysis of Heavy-Element Ions from Laser-Produced Plasma

L. LÁSKA, B. KRÁLIKOVÁ, J. KRÁSA, K. MASEK, M. PFEIFER, K. ROHLENA, J. SKÁLA, IP ASCR; E. WORYNA, P. PARYS, J. WOLOWSKI, IPPLM; W. MRÓZ, IO MUT; H. HASEROTH, H. KUGLER, N. LISI, H. MAGNUSSON, R. SCRIVENS, CERN; B. SHARKOV, ITEP

The operation principle of the Thomson parabola spectrograph (TPS) is based on the passage of ions through parallel electric and magnetic fields. It is an excellent device to give a general overview of the charge states and the velocity (energy) distributions of all the types of ions, produced in one single laser shot when used with a laser ion source. A program has been developed for the evaluation of the registered signals and for further data processing. Using the TPS and other diagnostics based on the time-of-flight method - ion collectors and the cylindrical electrostatic analyzer of the energy of ions - the laser produced plasma of different heavy elements was analyzed. As target material Ta, W, Pt, Au, Pb and Bi was chosen. The photodissociation iodine laser system PERUN was used for this purpose and results are compared with those obtained with the CO₂ laser ion source at CERN. Ionization and recombination processes in the expanding plasma will be discussed, with regard to the extraction of the ions from the expanding plasma at large distances from the target.

TH4052
Ion Sources for the New High Current Injector at GSI

P. SPÄDTKE, H. EMIG, K.D. LEIBLE, C. MÜHLE, H. REICH, GSI Darmstadt

The new high current injector at GSI (HSI) will replace the existing prestripper accelerator of Widerve type by a RFQ and an IH structure. This new accelerator will increase the possible particle currents up to two orders of magnitude. For the design ion Uranium, the particle current will be increased from presently 0.1mA (U10+) to 4mA (U4+). As ion sources for such high currents, a multi cusp ion source (for gases) or a vacuum arc ion source (for metals) are foreseen. The existing Penning ion source, which is well experienced for all elements of the periodic table, will be used in the future as well and has to be improved in current performance for this new operating regime.

TH4053
Enhanced H^- Ion Source Testing Capabilities at LANSCE*

W. B. INGALLS, M. W. HARDY, B. A. PRICHARD, O. R. SANDER, J. E. STELZER, R. R. STEVENS, LANL; K. N. LEUNG, M. D. WILLIAMS, LBNL

As part of the on-going beam-current upgrade in the Proton Storage Ring (PSR) at LANSCE, the current from the H^- injector will be increased from the present 16-18 mA to as much as 40 mA. A collaboration between the Lawrence Berkeley National Laboratory (LBNL) and the Los Alamos National Laboratory (LANL) has been formed to develop and evaluate a new ion source. A new Ion Source Test Stand ISTS has been constructed at LANL to evaluate candidate ion sources. The (ISTS) has been constructed to duplicate, as closely as possible, the 80 kV accelerating column, the beam transport, and ancillary systems presently in use in the LANSCE H^- injector, while incorporating additional beam diagnostics for source characterization. The construction and commissioning of the ISTS will be described, preliminary results for the proof-of principle ion source developed by the LBNL group will be presented, and future plans for the extension of the test stand will be presented.

* Work supported by the U.S. Department of Energy

TH4054
Development and Test Results of the Low-Energy Demonstration Accelerator (LEDA) Proton Injector on a 1.25 MeV CW Radio Frequency Quadrupole*

J. D. SHERMAN, G. BOLME, L. HANSBOROUGH, D. HODGKINS, E. MEYER, J. D. SCHNEIDER, H. V. SMITH, JR., M. STETTLER, R. R. STEVENS, JR., M. THUOT, T. ZAUGG, LANL; A. ARVIN, A. S. BOLT, M. RICHARDS, SRS; P. BALLEYGUIER, CEA/Bruyeres le Chatel; J. KAMPERSCHROER, General Atomics

The LEDA 75-keV proton injector is being developed for tests of high-current (100 mA) CW linacs. The injector comprises a microwave proton source and a space-charge neutralized magnetic low-energy beam transport system (LEBT). The LEDA injector has been configured to provide flexible 50-keV beam matching into a cw 1.25 MeV radio frequency quadrupole (RFQ) brought from Chalk River Laboratories [1]. The LEBT has two solenoid focus magnets separated by 117 cm. Between the solenoids are two steering magnets and diagnostic stations for measuring the beam current, profile, and position. The LEBT can match any reasonable ion source proton beam extracted into the RFQ. The ion source extraction system was modified to a 50 keV triode to test the injector/RFQ system. Beam matching tests showed that injector-RFQ transmission is 90% for 50-mA RFQ current. At the RFQ design current of 75 mA the beam transmission decreased to 80 - 85%. Aggressive injector tuning led to 100-mA beam accelerated through the RFQ. Design details for the 50-keV beam operation, and injector beam matching studies will be presented.

*Work supported by the U.S. Department of Energy.

Classification Category: T01

TH4055
Operation of a Microwave Proton Source in Pulsed Mode*

T. ZAUGG, C. ROSE, J. D. SCHNEIDER, J. SHERMAN, R. STEVENS, JR., LANL

Initial beam operation of the cw radio-frequency-quadrupole (RFQ) built for the Low Energy Demonstration Accelerator (LEDA) project requires the injection of a 75-keV, pulsed, H+ beam with a rise and fall time less than 10 microseconds and a pulse width from 100 microseconds to 1 millisecond at a repetition rate up to 10 Hz. The ion source for the accelerator is a microwave proton source driven by a 2.45 GHz magnetron. Pulsed beam from the injector is accomplished by modulation of the magnetron tube current. The magnetron provides microwave pulses to the ion source, and a medium-bandwidth, extraction power supply accelerates the H+ ion beam using a four-electrode extractor. A similar ion source with a three-element extractor operating at 50 kV has also been tested with this magnetron modulator. We report the results of modulating the ion source microwave power and extracting a pulsed proton beam using both a triode and a tetrode extractor.

*Work supported by the U.S. Department of Energy.

TH4056
Physics Design of the DARHT Electron Beam Injector*

E. HENESTROZA, UC-Davis; S. YU, S. EYLON, W. FAWLEY, LBNL

An injector for the for the second phase of the Dual-Axis Radiographic Hydrotest Facility (DARHT) is been designed at LBNL. The proposed injector consists of a single gap diode extracting 4 kAmps, 3.0 MV electrons from a thermionic dispenser cathode and powered through a high voltage ceramic insulator column by a Marx generator. The key issues in the design are the control of beam quality to meet the DARHT final focus requirements and to minimize high-voltage breakdown risks. We will present the physics design and beam dynamics simulations of the injector.

*The work was performed under the auspices of the U.S. Department of Energy under contract AC03-76SF00098.

TH4057
The Frankfurt H^- Source for European Spallation Source (ESS)

K. VOLK, A. MAASER, H. KLEIN, IAP-Univ. of Frankfurt

For the European Spallation Source (ESS) two ion sources are required, each delivering 70 mA of H^- ions during a 1.2 ms pulse and at a repetition rate of 50 Hz. In Frankfurt a H^- volume source, based on the HIEFS (high efficiency source) is being developed and tested. The source consists of a cesium seeded multicusp plasma generator, where negative ions are produced via volume and surface processes. During the last year, improvements of the cesium injection method enhance the beam current density up to already 120 mA/cm². Up to now, a H^- beam current of 80 mA has been extracted using an aperture radius of 5 mm.

The paper reports about the recent developments of the Frankfurt H^- source. After a description of the ion source and the experimental setup, measurements of the beam current density, the electron to H^- ratio, the lifetime of the source and an emittance estimation will be presented.

TH4058
Implementation of Improved Interactive Image Analysis at the Advanced Photon Source (APS) Linac*

N. ARNOLD, W. BERG, S. BIEDRON, A. LUMPKIN, S. MILTON, M. WHITE, B. YANG, ANL

An improved image analysis system based on commercially available data visualization software (IDL) allows a convenient interaction with image data while still providing calculated beam parameters at a rate of up to 2 Hz. Image data are transferred from the IOC to the workstation via EPICS channel access, thus, creation of a custom EPICS record was necessary to overcome the channel access limit of 16k bytes per array. The user can conveniently calibrate the screens, capture background images, acquire and average a series of images, and specify several other filtering and viewing options. The images can be saved in an APS-standard format (SDDS), allowing for rapid postprocessing of image data by numerous other software tools.

* Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

TH4059  (oral poster TH3006)
Non-Interceptive Emittance Measurement of a High Intensity Beam at Low Energy

P.-Y. BEAUVAIS, R. FERDINAND, R. GOBIN, B. POTTIN, CEA/Saclay

A CW Electron Cyclotron Resonance source has been constructed at CEA-Saclay and is now under test. The aim is to reach a 100 mA proton current at 95 keV with an rms normalized emittance smaller than 0.2 .mm.mrad and a very high reliability. In order to match this beam into the Radio Frequency Quadrupole linac (RFQ), its characteristics have to be monitored on-line. An emittance measurement unit (EMU) located close to the RFQ entrance is a very powerful diagnostic tool. We developed a non-interceptive EMU based on the video analysis of the residual gas illumination. Methods and results are presented and discussed.

TH4060

Contribution withdrawn.

TH4061
Bunch Length and Velocity Measurement of the JHP-RFQ Beam with INR BLVD

A. V. FESCHENKO, V. A. GAIDACH, S. A. KRIOUKOV, A. A. MENSHOV, P. N. OSTROUMOV, INR RAS; A. UENO, KEK

The bunch length and velocity of a beam accelerated with the 432-MHz, 3-MeV JHP-RFQ (Japanese Hadron Project - Radio Frequency Quadrupole) linac were measured by using a Bunch Length Velocity Detector (BLVD) developed by INR. The measured velocity (0.08002 ± 0.00016)c as well as bunch shape showed a good agreement with the simulation results. The longitudinal profiles of the bunch have been measured for various setting of the RFQ. The bunch shapes of H-minus beam as well as proton beam (produced by the stripping of H-minus ions) have been studied. Although the BLVD has been designed for measurement of beam core (~99% of particles) the accurate study of beam halo particle has been done. An almost uniformly distributed background noise signal in every longitudinal position was observed. The amount of the integrated noise signal was about 1% of the beam intensity. A possible source of the noise is analyzed.

Classification Category: T02

TH4062

Contribution withdrawn.

TH4063
Roll Bar X-ray Spot Size Measurement Technique*

R. A. RICHARDSON, T. L. HOUCK, LLNL

Dynamic effects such as backstreaming ions and electron-beam-plasma interactions can adversely effect the x-ray spot behavior of advanced, multishot, radiography machines. A time dependent x-ray spot size measurement is therefore critical to understanding beam target interaction physics. The so-called roll bar measurement uses a heavy metal material, which is optically thick to X-rays, to form a shadow of the x-ray spot. This spot is a result of the interaction of the energetic electron beam with a high Z target. The material (the "roll bar") has a slight radius to avoid alignment problems. A beam profile is assumed (or measured by other means) and the equivalent x-ray spot size is calculated from the x-ray shadow cast by the roll bar. Typically a radiographic film is exposed over the duration of the beam pulse and the shadow is analyzed for a time integrated measurement. This paper explores various techniques to convert the x-rays to visible photons that can be imaged using a gated camera or streak camera for time evolved x-ray spot size. Data will be presented from the measurements on the ETA II induction linac.

*Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under contract W-7405-ENG-48.

TH4064
Development of Nanometer Resolution C-band Radio Frequency Beam Position Monitors in the Final Focus Test Beam*

T. SLATON, G. MAZAHERI, SLAC; T. SHINTAKE, KEK

Using a 47 GeV electron beam, the Final Focus Test Beam (FFTB) produces vertical spot sizes around 70 nm [1]. These small beam sizes introduce an excellent opportunity to develop and test high resolution Radio Frequency Beam Position Monitors (RF-BPMs). These BPMs are designed to measure pulse to pulse beam motion (jitter) at a theoretical resolution of approximately 1 nm [2]. The beam induces a TM₁₁₀ mode with an amplitude linearly proportional to its charge and displacement from the BPM's (cylindrical cavity) axis. The C-band (5712 MHz) TM₁₁₀ signal is processed and converted into beam position for use by the Stanford Linear Collider (SLC) control system. Presented are the experimental procedures, acquisition, and analysis of data demonstrating resolution of jitter near 25 nm. With the design of future e⁺e^- linear colliders requiring spot sizes close to 3 nm [3], understanding and developing RF-BPMs will be essential in resolving and controlling jitter.

*Work supported by the Department of Energy, contract DE-AC03-76SF00515.

Classification Category: T02

TH4065
A High Peak Power S-band Switching System for the Advanced Photon Source (APS) Linear Accelerator (Linac)*

A. E. GRELICK, N. ARNOLD, S. BERG, Y. W. KANG, R. L. KUSTOM, A. NASSIRI, J. NOONAN, M. WHITE, ANL

An S-band linear accelerator is used in the Advanced Photon Source injector and additionally will be used to support a low-energy undulator test line (LEUTL) and a free-electron laser. To provide optimum availability for these uses, an additional modulator-klystron subsystem has been built and a waveguide switching and distribution subsystem is being constructed. The combined subsystems provide a hot spare for any of the five S-band transmitters that power the linac and have been given the additional function of powering an rf gun test stand whenever they are not otherwise needed. The design considerations for the waveguide switching subsystem, topology selection, timing, control, and protection provisions are described.

* Work supported by the U. S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

TH4066  (oral poster TH3007)
Performance of an S-Band Klystron at an Output Power of 200MW

S. CHOROBA, J. HAMEISTER, S. JARYLKAPOV*, DESY

In order to provide RF power to the accelerating sections of a future S-Band linear collider, klystrons delivering 150MW of output power at a frequency of 2.998GHz are required. Two S-Band klystrons with a nominal output power of 150MW at a pulse duration of 3microsec. and a repetition rate of 50Hz were developed in a collaboration between SLAC, Philips, TH Darmstadt and DESY [1]. They were built and successfully tested at SLAC in 1994 and 1995 and then shipped to DESY to feed the accelerating sections of the S-Band test facility linac. In order to explore their power potential one of the klystrons was operated at an even higher output power of more than 200MW at the test facilty. HV pulses up to 610kV at a current of 780A were applied to the klystron cathode. This paper reports the results of the measurements of the various parameters of the klystron at this power level (e.g. output power, efficiency, perveance). It describes the performance and the limitations of the klystron in this power range.

*on leave from INR, Moscow

TH4067
Overview of the APT RF Power Distribution System*

M. MCCARTHY, General Atomics; M. LYNCH, LANL; T. OVERETT, General Atomics; D. REES, LANL; G. SPALEK, J. TOOKER, General Atomics

* Work supported by U.S. DOE contract: DE-AC04-96AL89607.

Classification Category: T04

TH4068
A Conceptual Design of RF System in the NSP Superconducting Linac at JAERI

E. CHISHIRO, Y. HONDA, Y. TOUCHI, N. OUCHI, K. HASEGAWA, J. KUSANO, M. MIZUMOTO, JAERI

We have performed a design study work of a high intensity proton accelerator proposed for Neutron Science Project (NSP) at JAERI. The NSP accelerator will consist of RFQ, DTL and superconducting (SC) linac. It should be operated both in pulse and CW for demands in the application. The SC linac accelerates hydrogen ion beams from 0.1 GeV to 1.5GeV. An accelerating structure of the SC linac is divided into several beta sections, since the particle velocity varies along the linac. The SC structure with 8 different beta section suppresses the beam emittance growth and reduces the linac length. This linac has 284 cavities and the length of 690m. Number of cavities driven by an amplifier is set to 4. One of those cavities has the surface peak field of 16MV/m and the RF parameters of 4 cavities are adjusted to distribute the same RF power. For a pulse operation with the peak beam current of 30mA, the peak power of 158kW/cav. is required at the high-beta end. The other hand, the power of 47kW/cav. is required for the CW operation accelerating a beam current of 5.33mA. The total RF powers for pulse and CW operation are 29MW and 8.6MW, respectively.

TH4069  (oral poster TH3008)
Development of the X-band Klystron Modulator at KEK

M. AKEMOTO, S. ANAMI, H. MIZUNO, S. TOKUMOTO, KEK; T. MAJIMA, Y. KOBAYASHI, IHI

Two kinds of modulators with a Blumlein pulse-forming network (PFN) to drive a 65 MW X-band pulsed klystron for the main linac of linear collider are under development at KEK. The first modulator consists of a 1:8 step up pulse transformer, and two PFN's, a thyratron switch tube and a resonant charging circuit which are housed in air. The second modulator consists of two PFN's, a 1:7 step up pulse transformer, a thyratron switch tube and a resonant charging circuit which are all housed in a cylindrical oil tank which also mounts the klystron. This paper describes the performance of these modulators. The improvements of the performance of the PFN and the pulse transformer are also presented.

TH4070
A New RF System for the Debuncher at the KEK 40-MeV Proton Linac

Z. IGARASHI, E. TAKASAKI, T. TAKENAKA, K. NANMO, KEK

The RF system for the debuncher was renewed to an all solid state amplifier last summer. The amplifier containing one hundred and eight power transistors on its output stage can deliver a 20kW stably at 201MHz, so the momentum spread of the linac beam can be decreased less than 1%. This new rf system for the debuncher and its operational results are described.

TH4071
C-band 50 MW Klystron Using Traveling-Wave Output Structure

Y. OHKUBO, Toshiba Co.; T. SHINTAKE, N. AKASAKA, H. MATSUMOTO, KEK

The second tube of the C-band 50 MW klystron : TOSHIBA E3746 #2 has been developed in the course of the C-band rf-system R&D [1]. It uses a /2 mode traveling-wave structure in the output-circuit in order to enhance the power-conversion efficiency. The three-cell disk-loaded structure was analyzed by the coupled-resonator model, and parameterized in a 3 x 3 matrix form. The electrical performance at a hot-condition was calculated by a particle-in-cell simulation code: FCI, which predicted a power efficiency of 48%. This paper describes the design details and the experimental results.

Classification Category: T04

TH4072
Efficiency Enhancement of RF-Pulse Compressor for C-band Linear Collider

M. YOSHIDA, Univ. of Tokyo; T. SHINTAKE, N. AKASAKA, H. MATSUMOTO, KEK

Utilizing the energy in the front part of the HV-modulator pulse, the power gain of the rf-pulse compressor will be enhanced. To compensate the phase slip in the klystron due to the voltage rise, we apply the phase modulation on the rf signal at the klystron input. A computer simulation predicted a power gain higher than 4.0 at the compression factor of 5, therefore the effective efficiency will exceed 80%. In the C-band linear collider, we use a three-cell coupled-cavity as the rf pulse compressor [1]. The phase modulator also compensates the voltage-swing associated with the coupled-cavity resonances and produces a flat-pulse output required for multi-bunch beam acceleration. This paper describes the figure of merit in this scheme as well as a possibility to apply the super-conductive cavity in the compressor.

Classification Category: T04

TH4073
Results and Lessons Learned from Conditioning 1 MW CW 350 MHz Coaxial Vacuum Windows

K. CUMMINGS, R. CORDOVA, D. REES, W. ROYBAL, LANL; S. RISBUD, UC-Davis; D. WILCOX, EEV

The reliability of the radio frequency (RF) windows on the Low Energy Demonstration Accelerator (LEDA) is critical to the success of the Accelerator Production of Tritium Program (APT). On the APT machine there will be over 1000 windows, each passing on the order of 250 kW of CW RF power. This power level is well above power levels historically used in RF windows. Based on the high-power RF test results of the RF window prototypes from vendors, the coaxial windows made by EEV Ltd. of Chelmsford, England, were selected for LEDA. This paper describes the high-power RF testing of the 15 EEV coaxial windows. The RF window diagnostic equipment, data acquisition system and test stand are described. The results of the high power RF testing of the windows are presented. The successes and failures in the conditioning, manufacturing and testing techniques of the windows are presented. The conditioning timeline, power profile and the conditioning waveform are also discussed.

TH4074
Solid State Power Amplifier as 805 MHz Master Source for LANSCE Side-Coupled-Cavity Linac*

J. LYLES, J. DAVIS, LANL

From 100 to 800 MeV, the LANSCE proton linac receives RF power from forty-four 1.25 MW klystrons at 805 MHz. A single master RF source provides a continuous high level phase and amplitude reference signal to drive the klystrons along the 731 meter-long linac through a coaxial transmission line. A single point failure of this system can deenergize the entire SCCL RF plant. The authors replaced a physically large air-cooled tetrode amplifier with a compact water-cooled unit based on modular amplifier plates developed at LANSCE. Each 800 Watt plate utilizes eight push-pull bipolar power transistor pairs operated in class AB. Four plates can easily provide the 2800 watt reference carrier from the low level RF system. A radial splitter and combiner parallels the modules. This amplifier has proven to be completely reliable after a year of operation without failure. A second unit was constructed and installed for redundancy, and the old tetrode system was removed in 1998. The compact packaging for cooling, DC power, impedance matching, RF interconnection, and power combining met the electrical and mechanical requirements. CRT display of individual collector currents and RF levels is made possible with built-in samplers and a VXI data acquisition unit.

*Work supported by the U.S. Department of Energy.

TH4075
LEDA LLRF Control System Characterization

A.H. REGAN, LANL; P. BALLEYGUIER, CEA; C.D. ZIOMEK, ZTEC

The Low Energy Demonstration Accelerator (LEDA) for the Accelerator for the Production of Tritium (APT) project will be built at Los Alamos National Laboratory. The low-level RF (LLRF) control system portion of this accelerator must perform many functions, of which the primary one is controlling the RF fields in the accelerating cavities. Plans have been made to provide for on-line characterization of the LLRF control system and the complete RF system through use of stimulus and response buffers, and a digital signal processor built into the field control system electronics. The purpose of this circuitry is to characterize the behavior of the entire RF system (klystron, waveguides, high power splitters, accelerator cavity, etc.). This characterization feature can be used to measure the performance of the closed loop system with respect to the open loop system, to provide an automated way to set loop parameters, to determine the cavity Q-curve, and to detect any abnormal behavior in the RF chain. The types of measurements include frequency and time-domain responses to given perturbations, amplitude modulations, etc. This paper will discuss types of algorithms that can be implemented and present a description and block diagram of the electronics to be used.

TH4076
LEDA RF Distribution System Design and Component Test Results*

W. T. ROYBAL, D. E. REES, LANL; L. TOOLE, SRS; M. MCCARTHY, General Atomics

The 350 MHz and 700 MHz RF distribution systems for the Low Energy Demonstration Accelerator (LEDA) have been designed and are currently being installed at Los Alamos National Laboratory. Since 350 MHz is a familiar frequency used at other accelerator facilities, most of the major high-power components were available. The 700 MHz, 1.0 MW, CW RF delivery system designed for LEDA is a new development. Therefore, high-power circulators, waterloads, phase shifters, switches, and harmonic filters had to be designed and built for this application. The final Accelerator Production of Tritium (APT) RF distribution systems design will be based on much of the same technology as the LEDA systems and will have many of the RF components tested for LEDA incorporated into the design. Low power and high-power tests performed on various components of these LEDA systems and their results are presented here.

* Work supported by the US Department of Energy.

TH4077
A Thermal Analysis and Optimization of the APT 210 kW RF Power Coupler*

J.A. WAYNERT, F.C. PRENGER, LANL

This paper presents the thermal analysis and heat load optimization of the 210 kW, 700 MHz RF power coupler (PC) for the Accelerator Production of Tritium (APT). The PC is a co-axial design with RF power transmitted in the annular region between two concentric cylinders. Thermally, the PC represents a link from room temperature to the superconducting niobium cavities operating at 2 K. The PCs represent the second largest thermal load on the 2 K system, only the cavities generate a larger heat load. Thus, the objective of the analysis is to minimize the total refrigeration input power subject to manufacturability and availability constraints and refrigeration plant capital and operating cost concerns. The analysis includes all the major heat transfer mechanisms: conduction, RF joule heating in normal and superconducting materials, infra-red radiation, and, forced and natural convection cooling of the inner and outer conductors. A performance comparison is given for one and two single point thermal intercepts, versus a counter-flow heat exchanger on the outer conductor. The benefits of reducing the operating temperature of the center conductor are discussed. The variation in thermal performance of the inner and outer conductors with operating modes is also presented.

* Research supported through U.S. Department of Energy.

TH4078
A Multi-Moded RF Delay Line Distribution System for the Next Linear Collider (NLC)

S. G. TANTAWI, C. ADOLPHSEN, G. BOWDEN, Z. D. FARKAS, J. IRWIN, K. KO, N. KROLL, T. LAVINE, Z. LI, R. LOEWEN, R. MILLER, C. NANTISTA, R. D. RUTH, J. RIFKIN, A. E. VLIEKS, P. B. WILSON, J. WANG, SLAC

The Delay Line Distribution System (DLDS) is an alternative to conventional pulse compression which enhances the peak power of an rf source while matching the long pulse of that source to the shorter filling time of the accelerator structure. We present a variation on that scheme that combines the parallel delay lines of the system into one single line. The power of several sources is combined into a single waveguide delay line using a multi-mode launcher. The output mode of the launcher is determined by the phase coding of the input signals. The combined power is extracted using several mode extractors, each of which extracts only one single mode. Hence, the phase coding of the sources controls the output port of the combined power. The power is, then, fed to the local accelerator structures. We present a detailed design of such a system, including several implementation methods for the launchers, extractors, and ancillary high power rf components. The system is designed so that it can handle the 600 MW peak power required for the second stage of the NLC design, while maintaining high efficiency.

TH4079

Contribution withdrawn.

TH4080

Contribution withdrawn.

TH4081
DXRL Fabrication and Measurement of Millimeter Wave Accelerating Structures *

Y. KANG, J. SONG, A. NASSIRI, R. KUSTOM, ANL

Millimeter-wave accelerating cavity structures have been manufactured using the deep x-ray lithography (DXRL) technique. So far two prototypes have been made: a 30-cell constant impedance structure for 108-GHz and a 66-cell constant gradient structure for 94-GHz. These prototypes were designed and built to study the feasibility of building precision traveling wave cavities operating at millimeter-wavelength frequencies for compact linear accelerators. Basic radio frequency and mechanical properties have been measured for future improvement. Millimeter-wave characteristics were checked using an HP8510C 26-GHz vector network analyzer setup with a frequency up-converter and a frequency down-converter before and after a test cavity structure.

* Work supported by U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

TH4082
Niobium Spoke Cavities for a Superconducting Light-ion Linac

K. W. SHEPARD, ANL; J. R. DELAYEN, TJNAF; M. KEDZIE, ANL; C. PILLER, TJNAF

This paper reports the development of 350 MHz niobium superconducting cavities for accelerating particles over the velocity range 0.2 < v/c < 0.6. Such cavities could be used to form a linac of exceptional flexibility, capable of efficiently accelerating beams of protons, deuterons, or any of a wide range of light ions at intensities sufficient for a production beam for a radioactive beam facility. Results of numerical modeling for several resonator geometries are discussed, and the design and construction status of prototype niobium cavities is presented.

TH4083
A Tapered Damped Accelerating Structure for CLIC

M. DEHLER, I. WILSON, W. WUENSCH, CERN

A new 30 GHz multibunch accelerating structure incorporating both damping and detuning has been designed for the Compact LInear Collider (CLIC). Each cell of the 150-cell structure is damped by its own set of four radial waveguides resulting in a Q of 16 for the lowest dipole mode. A simple linear taper of the beam-pipe dimension provides a detuning frequency spread of 2 GHz (5.4%). Predictions of the transverse wakefield levels in this structure have been made using both uncoupled, and two-band coupled equivalent circuit models with non-perfect loads. The short-range wakefield has been calculated to be about 1000 V/(pC.mm.m) decreasing to less than 1% at the second bunch and with a long time level below 0.1%. The fundamental mode properties have been calculated using general expressions derived for linearly-tapered group velocity structures.

TH4084
/2 Interleaved Cavity Developments for the Muon Experiment*

J.N. CORLETT, LBNL; H.G. KIRK, BNL; D. LI, LBNL; A. MORETTI, FNAL; W.C. TURNER, LBNL; R.B. PALMER, Y. ZHAO, BNL

In this paper we discuss the development of a /2 interleaved standing wave linac for the proposed Muon cooling experiment. The nominal beam momentum is 186 MeV/c (ß=0.87). Each Muon cooling channel section contains a 1.3m rf accelerating linac separated by 0.64m of liquid hydrogen absorbers immersed in an alternating superconducting solenoidal magnetic transport line. Instead of conventional open cavity beam apertures, the 805 MHz linacs have thin Be windows covering iris apertures. The accelerating cavities closely resemble pillbox cavities and have little or no field enhancement due to iris aperture corners. Further, since the peak field is on the axis, the shunt impedance is about a factor 2 larger than conventional designs. It is also proposed to cool the cavity to liquid nitrogen temperature to reduce the losses and therefore, also increase the shunt impedance. Our /2 interleaved cavity design is essentially two chains of side coupled /2 cavities interleaved to form continuous chains of accelerating cells on the beam axis. Each accelerating cell has a phase advance of /2 and therefore, a favorable transit time factor. This paper will discuss the design of the cavity, MAFIA calculations, low-power rf model cavity measurements, low-temperature effects with Be windows, design of high-power rf test models and proposed high rf power test facility.

*Work supported by th e U.S. Department of Energy under contract No. DE-AC02-76CH03000.

TH4085
Scale Room Temperature Model of the Superconducting RFQ1 for the PIAVE Linac

V. ANDREEV, G. BISOFFI, M. COMMUNIAN, A. LOMBARDI, A. PISENT, A.M. PORCELATO, INFN-LNL; T. SHIRAI, ICR-Kyoto University

The new injector PIAVE (Positive Ion Accelerator for Very-low Energy) will use two bulk niobium (Nb) superconductng RFQs (SRFQ1 and SRFQ2), which will be operated at 80 MHz. The electrode length of SRFQ1 is about twice as long as SRFQ2 thus requiring an EBW vacuum chamber larger than the previosly available one. A principal decision was hence taken to split the electrodes and the tank into two parts. A half-scale room temperature model was built at LNL in order to test RF characteristic of the structure and to determine its exact dimensions. Results of the model measurements and MAFIA code simulations are presented.

TH4086
Equivalent Lumped Circuit Study for the Field Stabilization of a Long Four-vanes RFQ

A. PISENT, INFN-LNL; R. CELENTANO, INFN-LNL and University of Naples; R. ZENNARO, INFN-LNL and University of Ferrara

The possibility to design an RFQ long respect to the rf wavelength is very important for the feasibility of linacs with different applications, from the high power CW linacs for neutron production to the low power high frequency linacs proposed for hadrotherapy. In particular INFN has been funded for the study of the critical parts of a waste transmutation linac. In this framework the field stabilization of a 352 MHz RFQ has been studied, using the LANL resonant coupling technique; an equivalent lumped circuit approach has been used, and compared with MAFIA simulations. Based on the results of these studies an aluminum model (1:1 scale, 0.04 mm tolerances) has been built and we are now ready for the test of the tuning procedure.

TH4087

Contribution withdrawn.

TH4088
The Possibility of Multipactor Discharge in Coupling Cells of Coupled Cells Accelerating Structures

V.V. PARAMONOV, S.G. TARASOV, INR RAS

The multipactor discarge takes place at low values of electric rf field. Operating values of the field in accelerating cells are usually much more higher than the upper threshold of the discharge and this phenomenon takes place during structure conditioning. In operating regime, during rf pulse, weak electric field, linearly decreasing from the point of the rf drive to the end of the cavity, exists in coupling cells to provide rf power flux along the cavity. Depending on cavity operating regime and coupling cells parameters, the value of this field can be in limits of the discharge. In this paper parameters of coupling cells for side coupled, on-axis coupled and annular coupled structures are considered and estimations for electric field are given. Results of numerical simulations of the discharge in coupling cells are presented.

TH4089
Progress Work in a 27 MHz Heavy Ion RFQ

V. ANDREEV, D. KASHINSKY, A. KOLOMIETS, S. MINAEV, V. PERSHIN, R. VENGROV, V. ZVIAGINTSEV, S. YARAMISHEV, ITEP; G. PARISI, IAP-Univ. of Frankfurt

A 27 MHz heavy ion RFQ is now under construction at ITEP. It based on new ring-connected resonant structure. This structure is low frequency version of previously described "four-ladder" structure. The RFQ has been designed for acceleration of heavy ions with charge to mass ratio 1/60 to energy 110 keV/u. At present the manufacture of the structure is completed, RFQ is assembled and installed into a vacuum tank. The RF measurements confirm the expected parameters calculated by MAFIA and SOPRANO codes - resonant frequency, very reliable mode separation and perfect electrical field distribution. The carried out numerical simulations and experimental results show that given RFQ type is considerably promising candidate for use as initial part of high current heavy ion linac for HIF.

TH4090

Contribution withdrawn.

TH4091

Contribution withdrawn.

TH4092

Contribution withdrawn.

TH4093
Calculations of External Coupling to a Single Cell RF Cavity

D. LI, R. RIMMER, S. KOSTA, LBNL

A method is proposed to calculate the intrinsic and external Q values of a cavity coupled to a waveguide using MAFIA code in time domain. Typical methods used for the Q calculation in time domain are also reviewed. The method works efficiently for high Q cavities with coupling strengths close to critical coupling case. Applications of the method to a single cell rf cavity coupled to a waveguide are presented. The comparisons between the simulation and experimental results are given for a set of different coupling iris apertures.

TH4094
Mechanical Design, Construction and Alignment of the ISAC RFQ Accelerator at TRIUMF

G. STANFORD, D. PEARCE, R. L. POIRIER, TRIUMF

The ISAC RFQ is an 8 meter long, 4-rod split-ring structure operating at 35 MHz in CW mode. The rods are vane-shaped and supported by 19 rings spaced 40 cm apart. The stringent, ± 0.08 mm, quadrature positioning tolerance of the four rod electrodes over the 8m length was met by adopting a design philosophy based on manufacturing 19 identical rings and mounting them on precision ground platens which are accurately aligned in the vacuum tank prior to ring instalation. The accurately made components are assembled on a special assembly fixture and the electrode mounting surfaces are final machined in a jig after ring assembly using non-contact electrical discharge machining (EDM). The basic design of the ring is unique in that the RF surfaces have been de-coupled from the mechanical support structure to improve dynamic stability. The vacuum tank is also unique in that it is square in cross-section and split diagonally to obtain full unobstructed side access to the RFQ modules. The three dimension theodilite intersection method was used to accurately align two platen bases in the tank to allow 7 of the 19 rings to be installed in the first section of the 8m long vacuum tank.

TH4095

Contribution withdrawn.

TH4096
Engineering Design of the APT Cryomodules*

B.M. CAMPBELL, J.P. KELLEY, R. VALICENTI, J.A. WAYNERT, LANL

The high energy section of the Accelerator Production of Tritium (APT) linac uses superconducting radio frequency (SRF) cavities to accelerate a 100 mA proton beam from 211 MeV to 1700 MeV. Since SRF cavities can accept protons over a wide range of energy, only 2 different beta cavities are required; however 3 different length cryostats, or cryomodules, are required primarily to accommodate the changing magnet focussing lattice. A modular approach that will reduce the engineering and design effort required to produce these cryomodules has been adopted. The cavities will be cooled in a 2.15 K superfluid helium bath similar to that used by the Continuous Electron Beam Accelerator Facility (CEBAF). The comparatively short development time span for these cryomodules has led us to adopt many other design features from proven operating cryomodules. What sets the APT cryomodules apart is the comparatively high RF power. Although nearly 100% of the power is delivered to the beam, the RF losses occurring in the cavities and power couplers still place a large heat load on the refrigeration system. Reducing RF losses is a high design priority for these cryomodules, and analytical methods developed to define and minimize these losses will be described.

*Research supported through U.S. Department of Energy.

TH4097  (oral poster TH3009)
Progress of APT Superconducting Linac Engineering Development*

K. C. D. CHAN, B. M. CAMPBELL, R. C. GENTZLINGER, J. P. KELLEY, B. RUSNAK, H. SAFA**, LANL

We initiated a program to develop superconducting (SC) RF for high-power proton linacs. These linacs are useful in accelerator-driven transmutation technologies and the Accelerator Production of Tritium (APT) Project. We are developing multicell niobium cavities with elliptical-cell shapes at 700 MHz. These cavities, unlike most elliptical cavities for electron accelerators, are designed to accelerate protons at beta less than 1. Coaxial power couplers are being developed to transmit high (250 kW) CW RF power to the cavities. The couplers will be tested both at ambient temperature and at cryogenic temperature (2K). Their power handling and thermal properties will be measured. The cavities and power couplers will be integrated into a prototype cryomodule. The cryomodule will be tested and characterized with RF under cryogenic conditions required for a high-power proton linac. This paper describes the status of this program.

* Work supported by the U.S. Department of Energy.
** Scientist from CEA/Saclay, France

TH4098
Analysis of Performance Limitations for Superconducting Cavities*

J.R. DELAYEN, C.E. REECE, L. DOOLITTLE, TJNAF

The performance of superconducting cavities in accelerators can be limited by several factors, such as: field emission, quenches, arcing, rf power; and the maximum gradient at which a cavity can operate will be determined by the lowest of these limitation for that particular cavity. The CEBAF accelerator operates with over 300 cavities and, for each of them, we have determined the maximum operating gradient and its limiting factor. We have developed a model that allows us to determine the distribution of gradients that could be achieved for each of these limitations independently of the others. The result of this analysis can guide an R&D program to achieve the best overall performance improvement. The same model can be used to relate the performance of single-cell and multi-cell cavities.

* Work supported by the U.S. DOE Contract # DE-AC05-84ER40150.

TH4099
Resonance Control Cooling System for the APT/LEDA RFQ

R. FLOERSCH, G. DOMER, AlliedSignal

Cooling System layout is described as well as its operation to achieve the desired inlet temperatures in each of the four RFQ segments. Use of flow regulating valves to achieve uniform flow distribution to the 300 plus channels is discussed which also enables use of centrifugal pumps. Control system schema is described to regulate resonance frequency during steady state operation.

TH4100

Contribution withdrawn.

TH4101
First Tests of a Traveling-Wave Chopper for the ATLAS Positive Ion Linac*

R.C. PARDO, J.M. BOGATY, B.E. CLIFFT, ANL

A ten segment traveling-wave chopper has been constructed and successfully tested at 5% of the design 12 MHz repetition rate. The chopper must remove unbunched tails from a partially bunched heavy-ion beam in order to avoid undue emittance growth in the linac and the production of undesirable satellite beam bunches. When poorly bunched beams travserse a chopper, the traditional sine-wave chopper produces unacceptable transverse emittance growth and unnecessary beam loss. Emittance growth and unnecessary beam losses are expected to be much reduced in the traveling wave chopper. These first tests have confirmed the validity of these claims, clearly showing much reduced transverse emittance growth as compared to the original sine-wave chopper and excellent selectivity for the desired beam. Details of these tests will be presented and compared to calculations. Operation of the new chopper at the full 12 MHz rate is the next goal. Development of a driver power supply capable of full CW operation will also be described.

* This work was supported by the U.S. Department of Energy, Nuclear Physics Division, under contract W-31-109-ENG-38.

TH4102
Electrostatic Beam Kicker in the LEUTL at the APS *

G. WALDSCHMIDT, Y. KANG, ANL

An electrostatic kicker that was recently installed in the Low-Energy Undulator Test Line (LEUTL) of the Advanced Photon Source at Argonne National Lab has been computer simulated. The electromagnetic simulation code MAFIA was used to evaluate the field distribution and its uniformity. The kicker features off center electrodes to accommodate a larger deflection angle. The two rectangular electrode plates have dimension 10 cm x l cm and are separated by 1 cm. Numerical simulations also evaluate the effects of the electrode locations on transverse and field uniformity.

* Work supported by U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. W-31-109-ENG-38.

TH4103
Improved Temperature Regulation of APS Linac Rf Components*

R. DORTWEGT, S. PASKY, M. WHITE, ANL

The temperature of the high-power linac rf components is regulated by water from individual closed-loop DI water systems. Temperature changes in the S-band high-Q SLED cavities result in undesirable changes in the positron beam energy, thus a temperature regulation better than ± 0.1 degree F is required. Modifications to the closed-loop water systems have enabled us to achieve a regulation of ± 0.05 degrees over long periods. Regulation philosophy and equipment will be discussed, and numerical results will be presented.

* Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

TH4104  (oral poster TH3010)
Development of a Fast Traveling-Wave Beam Chopper for the SNS Project*

S.S. KURENNOY, J.F. POWER, LANL

High current and severe restrictions on beam losses, below 1 nA/m, in the designed linac for the Spallation Neutron Source (SNS) require clean and fast - with the rise time from 2% to 98% less than 2.5 ns - beam chopping in its front end, at the beam energy 2.5 MeV. The development of new traveling-wave deflecting current structures, based on meander lines, is discussed. Three-dimensional time-domain computer simulations are used to study transient effects in the chopper and to optimize current structure design. Two options for the fast pulsed voltage generator - based on FETs and vacuum tubes - are considered, and their advantages and shortcomings for the case of the SNS chopper are discussed.

*Work supported by the U.S. Department of Energy.

TH4105
Experimental Results of the Active Deflection of a Beam from a Kicker System*

Y. J. CHEN, G. CAPORASO, J. WEIR, LLNL

A high current kicker has been designed and tested on the ETA-II beam line. A bias dipole which surrounds the kicker acts to deflect the beam in the DC mode. High voltage pulsers (10kV) with fast rise times (~10ns.) are connected to the internal striplines of the kicker. They are used to manipulate beams dynamically. Camera photos which show the switching of the beam from one position to another will be presented. Beam bug measurements of beam-induced as well as active steering will be shown. These will be compared with theoretical predictions [1].

*This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

Classification Category: T08

TH4106  (oral poster TH3011)
Characterization of a Variable Energy Deuteron RFQ System for Neutron Production

R.W. HAMM, AccSys Technology; B.R. KALA, U.A.S. TAPPER, J. GUZEK, Schonland Research Centre; C.B. FRANKLYN, Atomic Energy Corp. of South Africa

A compact dual energy radio-frequency quadrupole (RFQ) linac system, the LANSAR^TM Model DL-5 manufactured by AccSys Technology, Inc., is being employed as a fast neutron source for a radiographic facility in South Africa. This RFQ accelerator was designed to allow the acceleration of deuterium ions to either of two selected energies, 3.90 or 4.86 MeV, for injection into a high pressure windowless gas target that employs a rotating shutter. Precise deuteron beam energies are required for effective use of this neutron radiographic imaging technique. The beam size at the gas target must also be small because it determines the spatial resolution of the imaging system. The energy variation was accomplished by coupling two RFQ cavities with an adjustable rf power phase shift in the second one to provide two modes of operation, i.e. beam acceleration or beam transport. The beam dynamics code PARMULT was used to design this RFQ system and calculate the linac output beam parameters as a function of the phase shift between the two RFQ structures. Experimental measurements have been made on the output beam using a Rutherford back-scattering (RBS) technique and beam scanner developed for this system. In this paper we will describe the results of the RBS energy and beam size measurements, as well as their correlation with the design calculations.

TH4107

Contribution withdrawn.

TH4108  (oral poster TH3012)
Status of the INFN High Current SC Proton Linac for Waste Transmutation

C. PAGANI, G. BELLOMO, INFN-Milano-LASA; R. PARODI, INFN-Genova; P. PIERINI, INFN-Milano-LASA

INFN, jointly with ENEA, is working at the design study for an accelerator driven waste transmutation subcritical system, TRASCO. In particular, our group is studying the high energy section, above 100 MeV, of the high power (> 30 MW) proton linac driver at 350 MHz, following the guidelines we presented at the Linac'96 Conference. The funded activities include the overall conceptual design of the three section SC linac and the development and tests of prototypes for the cavities and cryomodules. An overview of the status and perspectives of these activities will be given in this paper.

TH4109
Characterization of High Power CW Klystrons and Its Application to Low Level RF Control

A. ROHLEV, D. REESE, LANL

The power gain, phase delay, and line harmonic spectrum of a 1.3 MW, 350 MHz, CW klystron amplifier have been measured as a function of input power. These measurements along with the frequency response of the klystron were taken at several constant perveance and constant impedance operating points. These results are used to enhance the performance of the low level RF control system.