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Working Group IV

Insertion Devices for Future Light Sources

Group Leader: Dr. Johannes Bahrdt
Rudower Chaussee 5
12489 Berlin, Germany
Fax: 49-30-6392-4632 

Questionnaire: Measured Performance Data of Third-Generation Insertion Devices 

Objective: There are three main topics of discussion for this working group: 
  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. 
Detailed questions concerning the topics above: 

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 
Topic #2: 
  • 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 
Topic #3: 
  • Wakefield effects 
  • Stabilization of magnets 
  • Radiation / heat damage 
  • Reliability of mechanical components 
  • Superconducting undulators 
Working Group Activities:  
Working Group Input/Output:
  • 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 
Schedule of Presentations to the Working Group:
Preliminary Time Schedule of Working Group IV -- 31.3.1999 
Session 1 (Tuesday, 2.0 h)
Long Planar Undulators 
  • 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) 
Session 2 (Wednesday, 1.75 h)
Circular Devices 
  • 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.) 
Session 3 (Wednesday, 1.5 h)
Circular Devices (contd.) 
  • 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 
Session 4 (Wednesday, 1 h)
Alignment and Optimization Strategies for Long Devices, Online Field/Quality Control 
  • 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 5 (Thursday, 1.5 h)
Combined meeting with Working Group II (1 h) 

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
Session 7 (Thursday, 1.5 h)
Small Gap Undulators, In-vacuum Undulators (contd.) 
  • 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 
Session 8 (Thursday, 2.0 h)
New Devices, New Ideas and Concepts, Report Preparation 
  • 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 
Information and Preparations Requested of Working Group Members: Group members making presentations are requested to bring color copies and, if possible, electronic files of their presentation material for inclusion in the workshop proceedings.
Information Requested of Other Working Groups: From Working Group II:

  • 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? 
From Working Groups II and III:

  • 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? 
From Working Group III:

  • 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? 
Information Requested of This Working Group by Other Working Groups: Requested by Working Group II:

  • 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. 
Requested by Working Group III:

  • Are there any innovations in insertion device design that should be taken into account in exploring the limits of storage ring performance? 
List of Working Group Participants:
Zhonghou Cai ANL
Patric Den Hartog ANL
Bruno Diviacco Sincrotrone Trieste
Pascal Elleaume ESRF
Mikael Eriksson Max Lab
Kuanjun Fan NSRL, USTC
Efim Gluskin ANL
Hiroyuki Hama Institute for Molecular Science
Ching-Shiang Hwang SRRC
Gerhard Ingold Paul Scherrer Institut
Daoman Jiang NSRL, USTC
Hideo Kitamura SPring-8
Eric Landahl LLNL
Marie-Paule Level Projet SOLIEL
Herbert O. Moser Forschungszentrum Karlsruhe
Kazuhito Ohmi KEK
Mike Poole CLRC Daresbury Lab
George Rakowsky BNL
Matti Ryynanen VTT
Ross Schleuter LBNL
Lei Shang NSRL, USTC
Roman Tatchyn SSRL
Isaac Vasserman ANL
Xiangqi Wang NSRL, USTC
Udo Weinrich ESRF
Ming Xie LBNL
Shengian Xu ANL
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