1. Injector Setup for G0 and HAPPEX & Lessons Learned
Reza Kazimi

2. Layout of the Injector

3. Beam Requirements During G0 Run
Beam Parameters
Hall A
Hall B
G0 in Hall C
Current
100mA
Few nA
40mA
Charge/bunch
0.2 pC
2e-17 C
1.3 pC
Energy
1-5 GeV
sE/E
2.5x10-5
<10-4
5.0x10-5
Size at target
>100 mm
<1000mm
100mm
<200 mm
Divergence --
100mrad
100 mrad
Fractional Beam Halo
100Hz/mA
@R=3mm
>0.5mm
R>3mm
Polarization
>70%

4. Challenges How to transport high bunch charge beam in the injector
How to transport high and low bunch charge beams simultaneously through the injector
How to maintain parity quality

5. Solution
Extra bunching was done early in the injector to compensate for the space charge effect
The longitudinal optics were changed to accommodate the extra energy spread due to over-bunching
The laser spot size was increased to make a larger beam with lower space charge
Transverse optics were modified to deliver a larger beam with minimized optical aberrations
RF phase drifts were stabilized to maintain the beam quality

6. G0 Injector Model Verified by Measurements
Transmission rate vs. prebuncher amplitude
Bunch longitudinal profile: PARMELA
Confirms longitudinal model
Bunch longitudinal profile: Measured
Emittance vs. Beam Current
Bunch longitudinal profile: Measured vs. model
Transverse model within factor of 2

7. HAPPEX-II Beam Requirements
Beam Parameters
Hall A
Current
100mA
Charge/bunch
0.2 pC
Energy
3.2 GeV
sE/E
< 10-3
Size at target
> 100 mm
< 1000mm
Divergence
200 mrad
Fractional Beam Halo
100Hz/mA
@R=3mm
Polarization
> 70%

8. HAPPEX-II Injector Setup
Most improvements made for G0 were also applicable to the HAPPEX experiment
We had essentially the same setup as G0, with less prebunching

9. Lessons Learned
There was significant value in keeping the beam centered on optical elements, both in reducing the space charge effects and in maintaining the parity quality.
Errors in longitudinal bunch setup due to RF drifts caused asymmetries both in current intensity and position. (We now have better RF stability so this problem should not be as significant this time around.)
We can run high and low current bunches in the injector while maintaining bunch length and energy spread; however, it is best to avoid simultaneously running experiments with difficult beam specs.

10. Lessons Learned (Continued)
There was orbit-related sensitivity with current asymmetry around the quarter-cryo which was not fully understood. This showed up both during the G0 run and HAPPEX.
The Operations staff need to be more involved in the process and have more information on what is being changed, monitored and measured so they can be more effective in helping their customer.

11. END