Transcript Injector Setup for G0 and HAPPEX & Lessons Learned Reza Kazimi Layout of the Injector Synchrotron Light Monitor 5 MeV Dump Chopper Prebuncher 1/4 Cryo Cryomodules Buncher Capture Gun#2 PCup A1 A2 Gun#3 FC#1 Bunchlength Cavity 500

Injector Setup for
G0 and HAPPEX
& Lessons Learned
Reza Kazimi
Layout of the Injector
Synchrotron Light Monitor
5 MeV Dump
Chopper
Prebuncher
1/4 Cryo
Cryomodules
Buncher Capture
Gun#2
PCup A1 A2
Gun#3
FC#1
Bunchlength
Cavity
500 keV Dump
Injection Chicane
FC#2
45 MeV Dump/Spectrometer
Beam Requirements During
Run
Beam Parameters
Hall A
Hall B
0
G
G0 in Hall C
Current
100mA
Few nA
40mA
Charge/bunch
0.2 pC
2e-17 C
1.3 pC
Energy
1-5 GeV
1-5 GeV
1-5 GeV
sE/E
2.5x10-5
<10-4
5.0x10-5
100mm
<200 mm
100mrad
100 mrad
Size at target
Divergence
Fractional Beam Halo
Polarization
>100 mm
<1000mm
-100Hz/mA
@R=3mm
--
<10-3 @
>0.5mm
--
<10-6 @
R>3mm
>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
1. Extra bunching was done early in the injector to
compensate for the space charge effect
2. The longitudinal optics were changed to
accommodate the extra energy spread due to
over-bunching
3. The laser spot size was increased to make a
larger beam with lower space charge
4. Transverse optics were modified to deliver a
larger beam with minimized optical aberrations
5. 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
Transmission Rate (percent)
100
Confirms longitudinal model
90
80
PARMELA
Simulations
70
Operating Point
60
BCM
Transmission
50
Faraday Cup/Polarized
Cup Transmission
40
Bunch longitudinal profile: Measured
30
20
RMS Norm. Emittance (mm-mrad)
0
0.2
0.4
0.6
0.8
1
1.2 1.4 1.6 1.8
Prebuncher Amplitude (kV)
2
2.2
2.4
Emittance vs. Beam Current
0.3
x,y emittance - PARMELA
0.25
Bunch longitudinal profile: Measured vs. model
0.2
0.15
0.1
x,y emittance - Measurements
0.05
Transverse model within factor of 2
0
0
5
10
15
20
Beam Current (uA)
25
30
35
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
Divergence
Fractional Beam Halo
Polarization
> 100 mm
< 1000mm
200 mrad
100Hz/mA
@R=3mm
> 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
1.
2.
3.
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)
4. 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.
5. 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.