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SRF Requirements and Challenges for ERL-Based Light Sources

SRF Requirements and Challenges for ERL-Based Light Sources. Ali Nassiri Advanced Photon Source Argonne National Laboratory. 2 nd Argonne – Fermilab Collaboration Meeting May 18, 2007. Acknowledgements. APS M. Borland, J. Carwardine, Y. Chae, G. Decker, L. Emery, R. Gerig, E. Gluskin,

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SRF Requirements and Challenges for ERL-Based Light Sources

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  1. SRF Requirements and Challenges for ERL-Based Light Sources Ali Nassiri Advanced Photon Source Argonne National Laboratory 2nd Argonne – Fermilab Collaboration MeetingMay 18, 2007

  2. Acknowledgements • APS M. Borland, J. Carwardine, Y. Chae, G. Decker, L. Emery, R. Gerig, E. Gluskin, K. Harkay, R. Kustom, V. Sajaev, N. Sereno, C. Yao, Y. Wang, M. White • JLAB G. Krafft, L. Merminga, R. Rimmer,

  3. Outline • Introduction • SRF Requirement and Challenges • Summary

  4. Introduction • Energy Recovery Linac (ERL) is a potential viable revolutionary option for future light sources. • Argonne Advanced Photon Source is considering ERL for its upgrade • Promise of very high brightness and transverse coherence • Extremely low emittance, equal in both planes • Very low energy spread • Picosecond pulses • Option for less current with high charge, femtosecond pulses.

  5. A Design Parameters Comparison ILC1 Light Source ERL2 1 Barry Barish, GDE/ACFA Closing Beijing 7/02/07 2Ali Nassiri, APS MAC, Nov. 15-16,2006

  6. SRF requirements • 7 GeV single pass cw linac • 400 multi-cell SRF cavities for main linac • Roughly 400 meter of rf linac • 10 MeV, 100 mA Injector linac ( 1 MW RF power) • Roughly 45 kW total losses ( dynamic and static losses) at 20K • Large complex • Extremely heavy cryogenic load • Robust and reliable power couplers (FPC) and HOM dampers • Complex low-level rf control for amplitude, phase stability and microphonics • Acceptable RF systems reliability and availability for beam up time

  7. Cavity Main Parameters • Multi-cell cavities with a larger number of cells would also improve linac packing factor, i.e., ratio of active length to total length • This will reduce the cost of the ERL linac, BUT • Strong HOM damping is essential with higher beam current which favors smaller number of cells (per cavity for two beams)

  8. Superconducting modules for ERLs • Superconducting modules for high average current ERL operation have not been yet been demonstrated. • Issues ( among others) that must be addressed are: • CW operation resulting in fairly high dynamic and static heat loads. • High-current operation and the resultant large HOM power that must be extracted to limit the cryogenic load and to ensure stable beam conditions (100’s of watts)1. • Small bandwidth operation ( almost negligible net beam loading), which makes the cavity operation particularly susceptible to microphonic detuning • More rf power • More complex LLRF system and controls 1 Ali Nassiri, APS MAC, Nov. 15-16,2006

  9. Cavity Designs for ERLs • Effect of residual resistance on AC power consumption ( non-BCS surface resistance)* With state-of-the-art 7 n residual resistance With ideal 1 n residual resistance Multi parameters cost optimization is extremely important. * Temperature dependent of Carnot efficiency of the cryoplant is included.

  10. Quality factor • To reduce refrigeration power, cavity quality factor should be improved • ERLs need higher Q0 at moderate gradients • Gradients of 15 to 20 MV/m is reasonable. It avoids field emission. • To reduce refrigeration power, cavity quality factor should be improved • ERLs need higher Q0 at moderate gradients • Gradients of 15 to 20 MV/m is reasonable. It avoids field emission.  CEBAF spec. CEBAF 12 GeV project spec.   ERL design goal  Single-cell 1.3 GHz cavity tested at 1.6K at Saclay

  11. Summary • SCRF technology for CW machines is advancing at a fast pace. • The fundamental principles of ERLs have been established. • Technical challenges are: • Cryogenic design for ERL needs a new approach to improve refrigeration efficiency to reduce plant construction and operation costs. • Design a high current CW-specific cryomodule to meet ERL design parameters requirement. • Develop a robust HOM damping system for high average beam current operation • Better understanding of field emission for high gradient in CW mode • Improve cavity quality factor ( 11011) • For CW operation highest fields are not important. Highest possible Q values at about 20 MV/m are very critical. • We are carefully considering the challenges presented by the ERL upgrade • CW-SRF technology R&D program for ERL will benefit from ANL-FNAL active collaboration • We are ready to start

  12. Acknowledgements M. Borland, J. Carwardine, G. Decker, L. Emery, R. Gerig, K. Harky, V. Sajaev, N. Sereno, M. White

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