The Polarized Electron Source for the International Collider ILC Project

1
The Polarized Electron Source for the
International Collider (ILC) Project

• A. Brachmann, Y. Batygin, J.E. Clendenin, E.L.
  Garwin, K. Ioakeimidi, R.E. Kirby, T. Maruyama,
  J. Sheppard, F. Zhou, C.Y. Prescott
• - SLAC -

2
Outline

• Introduction
• Parameters
• Layout
• RD and Design Status, Future Plans

3
ILC Schedule

• End of 06 Reference Design Report
• End of 09 Technical Design Report
• In 2010 Decision expected from funding
  agencies
• In 2012 Begin of construction

4
ILC Design Strategy

• International Collaboration (Americas, Europe,
  Asia)
• Global Design Effort is interaction of
• Area Systems (e.g. e- source, e source, linac,
  BDS, etc)
• Technical Systems (e.g. Magnet system, Vacuum
  system, instrumentation, etc.)
• Global Systems (e.g. Installation, Conventional
  facilities)
• Currently, cost of machine is evaluated and
  alternative designs are investigated to reduce
  overall cost

5
Polarized Source Parameters
6
ILC Pulse Train Illustration
7
Schematic Layout
8
Low Energy Beam Line and Bunching System
Simulations including Space Charge
matching triplet
Two 5-cell SW L-band
108MHz SHB
1st TW Structure
2nd TW Structure
433 MHz SHB
9
Physical Beam Line Layout
Superconducting Linac (5 GeV)
Combining Dogleg and Collimation
Spin rotation (SC Solenoid) ?
RF energy compression ?
10
Spin Rotation using Solenoids
Slongitudonal
7.5 m
5 GeV
Depolarization in arc due to energy spread
Bend of n 7.9312o
Odd Integer

• Arc bending angle ? 55.51o
• Spin precession angle ? (7/2)?
• Energy spread ??/? 0.02 GeV
• Depolarization (analytic) ?P/P 0.024
• Particle tracking ?P/P 0.007

ILC design n 7 ? 55.51o
11
ILC e- Source Facilities Layout
12
RD for the Polarized Electron Source (not
limited to activities _at_ SLAC)

• Laser Development
• Laser system beyond state of the art
• Challenge is 3 MHz amplification
• Demonstrate photocathode performance
• Photocathode Development
• ? See talks by T. Maruyama, K. Ioakeimidi
• Gun Development
• DC gun Improved HV performance
• Polarized RF gun explore feasibility of
  polarized RF gun
• ? See talk by J. Clendenin

13
Source Laser System
14
Laser Pulse Energy and Laser Power

• Cathode QE requires 2-10 µJ per micro pulse
• Modest total average power 70 mW
• 2820 pulses, 5 Hz, 5 µJ
• Average power in 1 ms burst 15 W
• 3 MHz, 5 µJ
• Need to design 15 W average power amplifier
  system
• Crystal cooling cryogenic (power dissipation,
  thermal lensing)

15
Laser System Schematic
16
PhotocathodesQE Profile Variation vs. Time

• Cathode is SVT4249 (strained layer GaAs/GaASP,
  2cm diameter),
• installed in SLACs polarized gun, serving
  main LINAC.

August 03
June 05
August 06

• Cathode can deliver charge
• QE profile degradation is obvious
• Further investigation under ILC conditions is
  needed

17
QE Profile August 06(Slice through Cathode
Center)
18
Number of Electrons generated from cathode
installed for 3 years (August 06)
ILC at source (6.4 nC)
ILC at IP (3.2 nC)
19
Gun Development

• Baseline design SLC Gun at 120 keV
• Higher Voltage Gun allows shorter bunches
• reduces requirements for bunching system and can
  improve timing flexibility due to possible
  elimination of 108 MHz SHB
• Examples for higher voltage guns are
• 200 keV _at_ Nagoya
• 350-500keV _at_ JLab, Cornell
• RD for Polarized RF Gun is being considered
• See talk by J. Clendenin
• Gun development for the ILC source design is part
  of our proposal for ILC RD work

20
Summary and Conclusions

• SLC source design is a good starting point for
  ILC
• ILC parameters are different ? RD needed
• Demonstrate cathode performance under ILC
  conditions
• ILC project contributes to advance the state of
  the art of polarized sources
• e- source is relatively small but important ILC
  RD effort