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

2May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri 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, Acknowledgements

3May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri Outline Introduction SRF Requirement and Challenges Summary

4May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri 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.

5May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri Beam Energy 500 COM 5 – 8GeV Average beam Current9.0100mA Bunch train repetition rate5 1.3  10 9 Hz RF duty factor 7.5   CW Average accelerating gradient31.520MV/m Cavity Quality factor 1  > 5  (1  ) Beam pulse length 9.5   sec Total AC power consumption~230~ 50MW A Design Parameters Comparison ILC 1 Light Source ERL 2 1 Barry Barish, GDE/ACFA Closing Beijing 7/02/07 2 Ali Nassiri, APS MAC, Nov ,2006

6May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri 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 2 0 K –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

7May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri Cavity Main Parameters ParameterUnitValue FrequencyMHz1300/1408/704 Accelerating mode TM 010  mode GradientMV/m18/20 Quality factor Q 0 2  /1  Number of cells9/7/5 ( HOM problem) R/Q  900/1200 Q ext for input coupler 1  10 7 Cavity bandwidth at Q ext Hz400 Fill time ss 500 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)

8May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri 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 ,2006

9May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri Cavity Designs for ERLs Effect of residual resistance on AC power consumption ( non-BCS surface resistance)* With ideal 1 n  residual resistance With state-of-the-art 7 n  residual resistance * Temperature dependent of Carnot efficiency of the cryoplant is included. Multi parameters cost optimization is extremely important.

10May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri Quality factor To reduce refrigeration power, cavity quality factor should be improved ERLs need higher Q 0 at moderate gradients Gradients of 15 to 20 MV/m is reasonable. It avoids field emission. Single-cell 1.3 GHz cavity tested at 1.6K at Saclay     CEBAF spec.  CEBAF 12 GeV project spec.  ERL design goal To reduce refrigeration power, cavity quality factor should be improved ERLs need higher Q 0 at moderate gradients Gradients of 15 to 20 MV/m is reasonable. It avoids field emission.

11May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri 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  ) 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

12May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri Acknowledgements M. Borland, J. Carwardine, G. Decker, L. Emery, R. Gerig, K. Harky, V. Sajaev, N. Sereno, M. White