Working Group IV

Insertion Devices for Future Light Sources

Questionnaire: Measured Performance Data of Third-Generation Insertion Devices 

1. The technology for 5m-planar insertion device production and optimization is well established. The limits for an extrapolation to long undulators (50-100m) shall be worked out. 
2. Various concepts for circularly polarizing undulators have been proposed and realized (pure permanent devices as well as electromagnetic devices). What are the specific problems compared to conventional planar devices and how can they be solved? 
3. Existing in vacuum insertion devices and other short period devices with small fixed gap or flexible gap vacuum chambers shall be compared and the working regions for the different concepts shall be pointed out. 

Topic #1: 

• What is the technical limit in total length for tunable gap undulators if the undulator is segmented and kicker and phase adjusting units between the segments are provided? 
• Are new magnetic field measurement techniques necessary? 
• Alignment of long undulators based on electron beam and or photon beam monitors 
• Which "knobs" must be provided for an online alignment of a long undulator (kickers, phase adjusters, stages for moving focusing elements or even complete undulator segments, etc.)? 
• Online check of magnetic field quality in long undulators 
• Coupling of undulator and monochromator 

• Is there an improvement in magnet block quality (homogenity) observable over the last years? 
• Specification and measurement of block inhomogenities 
• Sorting and shimming techniques for circularly polarizing permanent magnet undulators 
• What are the specific problems of long circularly polarizing undulators compared to planar devices? 
• Interaction of fast switching electromagnetic circularly polarizing undulators with the storage ring 

• Wakefield effects 
• Stabilization of magnets 
• Radiation / heat damage 
• Reliability of mechanical components 
• Superconducting undulators 

• Achieved accuracy of magnetic field measurements (Hall-probe, stretched wire etc.) 
• Achieved field qualities in terms of phase errors and integrated field errors 
• Achieved accuracy of mechanical drive systems 
• Interaction of existing insertion devices with the storage ring 
• Accuracy of electron beam and photon beam position monitors in storage rings 

• Kim: Kick errors and phase errors in high gain FEL performance 
• Rossbach: Status of the TESLA-FEL undulator 
• Liz Moog / Isaac Vassermann: The APS FEL undulator 
• Rakowsky: The strong focussing VISA undulator for SASE FEL 
• Eriksson: MAX-wiggler, a multipole superconducting device

(the talk is included into this session due to the time schedule of Mikael Eriksson) 

• Kitamura: Exotic undulators with special polarization characteristics 
• Diviaccio: Circularly polarizing devices at ELETTRA 
• Hwang: Insertion devices with variably polarized light at SRRC 
• Schlueter: The ALS EPU 
• Elleaume: Circularly polarizing devices at ESRF (3 Tesla asymmetric Wiggler, fast switching helical device etc.) 

• Kim: Generating circular polarization with crossed planar undulators in high gain FELs 
• Sasaki: Recent developments in quasiperiodic undulator design 
• Ryynanen: Inhomogenities and sorting algorithms 
• Bahrdt: The BESSY II double undulator UE-56, some aspects of block inhomogenities, first experience in the storage ring 

• Hama: beam based alignment of helical undulator 
• Tatchyn: Aspects of strong focussing undulator design for storage ring and linac-driven X-ray FEL (XRFEL) applications 

Session 6 (Thursday, 1.5 h) Small Gap Undulators, In-vacuum Undulators 

• Kitamura: Practical side of in-vacuum undulators 
• Rakowsky: Small-gap undulator development at the NSLS
• Schlueter: Planning of small gap insertion devices at the ALS

• Elleaume: experience with in-vacuum undulator at the ESRF 
• Udo Weinrich: Limitations on Minimum Gaps of Insertion Devices 
• Ingold: Plans for small gap operation at SLS 

• Tatchyn: A variable-period undulator design study for SPEAR
• Which codes are used and how do they compare? What is new? Which tools should be developed for a more efficient insertion device design? Are the interfaces between ID and machine (implementation of real devices into tracking codes) and between ID and beamline / monochromator (radiation properties) well defined? 
• Elleaume: SRW, RADIA 
• Bahrdt: PHASE 

• How fast can the electron energy of a LINAC be changed (on a continuous scale) for tuning the photon energy of a SASE FEL? What is the duty cycle of a LINAC in a multi-user facility if the electron energy has to be modulated in order to fit the user needs at several different undulators? 

• Tolerable trajectory wander and tolerable phase errors in long undulators. 
• Are there important tolerances that have not yet been addressed like second field integrals for quadrupole or sextupole errors? 

• What is the appropriate parameterization for specifying integrated multipoles of insertion devices in storage rings: 
1. multipole expansion with respect to the ID-center 
2. a transverse distribution of integrated fields 
3. something else 
• Is there a chance for energy spread reduction in third-generation storage rings? 
• Are the tracking tools for insertion devices sufficient and is there evidence from measurements that the codes yield correct answers? 

• State-of-the-art wiggler strength as a function of period and gap. 
• State-of-the-art strong focussing strength as a function of period and gap. 
• Rms dipole error as a function of period and gap. 
• Best achievable alignment precision (long range) 
• Period of BPM/corrector stations. 
• Deviation of the mean of the peak field values along the whole wiggler. 

• Are there any innovations in insertion device design that should be taken into account in exploring the limits of storage ring performance?