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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, - PowerPoint PPT Presentation
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SRF Requirements and Challenges for ERL-Based Light Sources
Ali Nassiri
Advanced Photon Source
Argonne National Laboratory
2nd Argonne – Fermilab Collaboration MeetingMay 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 – 8 GeV
Average beam Current 9.0 100 mA
Bunch train repetition rate 5 1.3109 Hz
RF duty factor 7.510-3 - 110-2 CW
Average accelerating gradient 31.5 20 MV/m
Cavity Quality factor 11010 > 51010
(11011)
Beam pulse length 9.510-4 210-12 sec
Total AC power consumption ~230 ~ 50 MW
A Design Parameters Comparison ILC1
Light Source ERL2
1 Barry Barish, GDE/ACFA Closing Beijing 7/02/07
2 Ali Nassiri, APS MAC, Nov. 15-16,2006
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 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
7May 18, 2007 ERL SRF Requirements and Challenges A. Nassiri
Cavity Main ParametersParameter Unit Value
Frequency MHz 1300/1408/704
Accelerating mode TM010 mode
Gradient MV/m 18/20
Quality factor Q0 21010 /11011
Number of cells 9/7/5 ( HOM problem)
R/Q 900/1200
Qext for input coupler 1107
Cavity bandwidth at Qext Hz 400
Fill time 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
WP
psspacingerbunchintMHzf
pCQ
HOM
bunch
||
b
150
770 1300
pCV 10
77
(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. 15-16,2006
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 resistanceWith 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 Q0 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
10
12
Q
Q
REm
P
macc
CEBAF spec.
CEBAF 12 GeV project spec.
ERL design goal
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.
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 ( 11011)• 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
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