Plenary Session Abstracts

The talk will review the workshop on Fourth-Generation Light Sources held on January 22-25, 1996, in Grenoble by highlighting the conclusions of the seven Working Groups (WGs).

Ring-based Sources Overview
V. Litvinenko, Duke University (e-mail: vl@phy.duke.edu)

More than fifty ring-based fully or partly dedicated light sources are in operation around the globe at present time and large number is in the construction or development phase. These rings operate at energies from few hundreds MeV to 14 GeV covering photons spectra from IR to soft gamma-rays.

This talk will be focused on three topics relevant to storage ring-based light sources. We will start from brief overview of existing ring-based sources and drawing a generic picture of ŅtypicalÓ second and third generation storage ring-based light sources to establish the base line. The table with range of established machine and light source parameters will be presented. It will be followed by discussion of new trends in the development of ring-based light sources which push the envelope of presently established parameters by reduction of e-beam emittances, increase of beam currents, shortening pulses, increasing coherence, etc. Third part of talk will be dedicated to evaluation of future capabilities and limitations of ring-based light sources. Few examples of new capabilities will be presented.

Overview of SASE Theory and Planned Experiments
C. Pellegrini, Univ. of California-Los Angeles (e-mail: pellegrini@physics.ucla.edu)

Abstract not yet received

Overview of Gun and Linac FEL Experimental Results
D. Nguyen, Los Alamos National Laboratory (e-mail: dcnguyen@lanl.gov)

Abstract not yet received

Advanced Insertion Device Practices and Concepts
H. Kitamura, SPring-8 (e-mail: kitamura@spring8.or.jp)

The world's first in-vacuum undulator, operated at KEK in 1990, was recognized as a domestic, exceptional, and momentary success. However, the technology has been developed on a large scale at SPring-8, where a great many in-vacuum undulators are being operated successfully. In addition, a short-period undulator with a very short gap has been realized at NSLS by collaborative work between BNL and SPring-8, which has produced a new concept of SR facility with a combination of low emittance ring and very short-gap undulators. In other words, we may have some possibilities for a design for a moderate-cost, medium-sized SR facility, the performance of which may be comparable to that of APS, ESRF, or SPring-8, a typical third-generation light source in the x-ray region. In the talk, we review the great potential of in-vacuum undulator technology.

Plasma-based X-ray Lasers
L. DaSilva, Lawrence Livermore National Laboratory/University of California (e-mail: dasilva1@llnl.gov)

Abstract not yet received

Femtosecond X-ray Science at the ALS: Recent Results and Future Plans
R. Schoenlein, Lawrence Berkeley National Laboratory (e-mail: RWSchoenlein@lbl.gov)

An important new area of research in chemistry, physics, and biology is the application of x-ray techniques to investigate structural dynamics associated with ultrafast chemical reactions, phase transitions, vibrational energy transfer, and surface dynamics. The fundamental time scale for the atomic motion associated with these processes is a single vibrational period (~100 fs). We have recently demonstrated the generation of femtosecond synchrotron pulses from the Advanced Light Source by using femtosecond optical pulses to slice a stored electron bunch. A new bend-magnet beamline is being developed for generating 100 femtosecond x-rays to investigate structural dynamics in condensed matter using time-resolved optical pump and x-ray probe techniques. Future plans include the development of an in-vacuum insertion device beamline providing high-brightness femtosecond x-rays.

Research with Coherent X-Rays at the Mainz Microtron MAMI
H. Backe, Institute fuer Kernphysik der Universität (e-mail: backe@kph.uni-mainz.de)

The Mainz Microtron MAMI is a modern electron accelerator delivering a high current and low emittance beam (100 µA c.w. and 1 pi nm rad, respectively) with an energy of up to 855 MeV. With the three electron spectrometer facility, a photon tagging facility, in combination with the possibility of polarizing the electron beam, a rich program has been carried through to investigate the structure of the atomic nucleus. In addition, a research program is underway to explore the features of varies radiation production processes covering the whole spectrum from the hard X-ray to the optical region. These are the Transition Radiation (TR), Parametric X Radiation (PXR), Undulator Radiation (UR), and Smith-Purcell Radiation (SPR).

A novel interferometer has been developed with which the complex index of refraction of thin self supporting foils can be measured in the VUV and soft X-ray region [1]. It consists of a collinear arrangement of two undulators in combination with a grating spectrometer. Distinct oscillations have been observed as a function of the distance between the undulators. A foil placed between the undulators causes a phase shift and an attenuation of the oscillation amplitude. Measurements of the complex index of refraction have been performed in the region of anomalous dispersion at the K-absorption edge of carbon. This interferometer principle can be extended into the hard X-ray region employing TR from thin foils instead of undulator radiation.

Parametric X Radiation (PXR), or quasi-Cherenkov radiation, is produced by passage of an electron through a crystal. The production mechanism of PXR has been investigated by measuring the angular distribution for several diffraction orders in silicon single crystals [2]. A critical absorber technique has been employed to measure the linewidth of PXR [3]. An upper limit of 1.2 eV has been determined for the (111) reflection of silicon at a photon energy of 4966 eV. Extremely narrow linewidths of about 5 meV are expected for the (444) reflection at 7908 eV in backward geometry.

A quasi-monochromatic hard X-ray beam with photon energies up to 50 keV can be produced by TR from a foil stack, see e.g., [4] and references cited therein, using a highly oriented pyrolytic graphite crystal. The contrast of dilute elements in a sample can be enhanced by a fast energy tuning around the K-absorption edge. This will be achieved at a fixed focus for every pixel of a pn-CCD detector by a synchronous variation of the crystal position and electron beam direction.

Smith-Purcell radiation (SPR) has been investigated in the optical spectral range. In the experiments an 855 MeV beam, focused to a spot size of 4 µm (FWHM), passed close at the surface of an optical diffraction grating. The well-known and specific emission characteristics of SPR were exploited to discriminate against various background radiation components. The measured intensities are in reasonable agreement with calculations on the basis of the Van den Berg model [5] if the blaze angle of the grating is not too flat.

[1] S. Dambach, et al., Phy. Rev. Lett. 80 (1998) 5473
[2] K.-H. Brenzinger, et al., Z. Phys. A 358 (1997) 107
[3] K.-H. Brenzinger, et al., Phys. Rev. Lett. 79 (1997) 2462
[4] H. Backe, et al., Z. Phys. A 349 (1994) 87
[5] P.M. Van den Berg, J. Opt. Soc. Am. 64 (1974) 325

UV Science with a 4th-Generation Light Source
E. Johnson, Brookhaven National Laboratory (e-mail: erik@bnl.gov)

Abstract not yet received

Abstract not yet received