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

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.

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)

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)

(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)

New IA under test

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.

ITS laser room

Where would the new stuff fit ?

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

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

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

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.

April’02 - emittance filter HC beam motion at an aperture induces a HC beam intensity. PZT mirror tests have yielded charge asymmetries of 300-400 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).

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)

Timeline May 2002 24th - G0 beam test Memorial day shutdown - install IA in Hall A laser @ 770 nm June-July 2002 Begin testing with new G0 helicity card No MD, but facility development and G0 beam test July-August 2002 - 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

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…?