1. Feedback Systems Joe Grames Hall A Parity Meeting Jefferson Lab
May 10, 2002

2. Goals for HC Feedback
Independent intensity control for each hall. This means providing parity quality intensity devices for both HAPPEx2 and G0.
Hall B continues with a diode laser and TACO feedback.
Independent position capability for the parity Halls (A&C).
Alternative controls for the HC devices (direct fiber or software).
Fast signal readback of the control devices (V-F-V’s).
Compatibility with 3-hall laser configuration.
Above all, provide users with what they require for successful experiments and continue to further JLab parity capabilities.

3. Our present layout... Each gun is equipped with
PZT X/Y mirror (testing only)
Insertable l/2-plate (systematic reversal)
Pockels cell (circular light and PITA)
Rotatable l/2-plate (corrective element)

4. Intensity Feedback
Use a low voltage Pockels cell for intensity modulation. PC a V
Intensity
l/n
Requirements:
indendent control
stable & sufficient gain
low insertion loss
low cell voltage
compact footprint
(Tsentalovich, BATES)

5. (insert here two plots showing I vs. a and dI/dV vs. a near V=0)
IA-l/10
(insert here two plots showing
I vs. a and dI/dV vs. a near V=0)

6. New IA under test

7. Position Feedback
We use a mirror on a fast PZT driven stage for HC position control. The present setup uses a single common mirror (last one) ~10 cm upstream of the polarization Pockels cell.
Independent position control requires multiple PZT mirrors for usual 3-laser combination.
This doubles the moment arm reaching the cathode, but also increases the distance to the Pockels cell to about 100 cm.
This capability could be installed during the summer shutdown, but
requires advance re-work of pico-mirror mounts used for laser steering.
The ITS laser room is an excellent resource for feasibility tests.

8. ITS laser room

9. Where would the new stuff fit ?

10. Device Controls Source DAQ
Hardware controls (V-F-V’s)
Feedback
Signals (fiber)
Source
(IA, PZT,RWP)
DAQ
(BPM,BCM)
Software control (Gateway/LockServer)

11. Helicity Lock Server Lock Server EPICS using Gateway 24/7 OPS coverage
Fast DAQ/Device config
1 year in service, 3 halls
Infrastructure for PZT

12. Injector Monitoring Two parity DAQ’s Signals TBA HAPPEx2 (ADC’s)
G0/INJ (Triumf V/F’s & scaler)
Provides redundancy for checkout & upgrades
Signals TBA
Injector cavity BCM
Two 100 keV BPM’s
Two 5 MeV BPM’s
HC feedback levels
Two batteries

13. April’02 - BPM work
Prior to the April shutdown 60 Hz content of beam intensity in Hall B ~10-20% sourced in
100 keV region.
During the April shutdown extensive effort to
identify, remove & isolate 60 Hz sources.
SEE BPM re-configured:
100 keV FFB
Additional S/H cards
Flexibility (3 vs 2 crates)
Hall B coming on line now - results in soon.

14. April’02 - emittance filter
HC beam motion at an aperture induces a HC beam intensity.
PZT mirror tests have yielded charge asymmetries of ppm/volt.
Two injector apertures (A1/A2) defined the old T-Gun beam emittance. The P-Gun emittance is defined at the source, so in preparation for G0
and to reduce HC effects new sets of apertures were installed with increased sizes (1x, 2x, 3x).
Initial tests are promising: using the 2x set resulted in a < 40 ppm/volt
over the full range of PZT voltages (1-9 volts).

15. Injector beam monitoring
Helicity correlated feedback from the injector is limited by the multi-user operation of JLab. The beam diagnostics “see” all beams in superposition.
Conceptual design for independent beam monitoring:
beam intensity modulation (~1 kHz) w/ lock-in technique
use of DSP and Digital Receiver VME boards
Andrew Hutton supports a feasibility
initial design to test injector BCM cavity 0L02 (earliest Fall 2002)

16. Timeline May 2002 24th - G0 beam test
Memorial day shutdown - install IA in Hall A 770 nm
June-July 2002
Begin testing with new G0 helicity card
No MD, but facility development and G0 beam test
July-August SHUTDOWN
Independent IA’s for A & C laser into tunnel
Independent PZT’s if desired are installed too
September-October 2002
Parity beam for G0 run period
Test capabilities for simultaneous parity beam (G0 & GDH)
March-August 2002
Parity quality beam for HAPPEx2
Laser TBD

17. Conclusions
This is an exciting time to be preparing
for the upcoming parity experiments.
We are looking forward to a strong
collaborative effort and for achieving
the design and controls you need.
So, what else…?