Injector Setup for G0 and HAPPEX & Lessons Learned Reza Kazimi

Layout of the Injector

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 <10-3 @ >0.5mm <10-6 @ R>3mm Polarization >70%

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

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

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

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%

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

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.

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.

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