srf requirements and challenges for erl-based light sources ali nassiri advanced photon source...

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


Outline

Introduction SRF Requirement and Challenges Summary


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.


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


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


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)


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


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.


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.


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


Acknowledgements

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

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