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Hall A Parity Meeting Jefferson Lab May 10, 2002

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.

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Hall A Parity Meeting Jefferson Lab May 10, 2002

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

  5. 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 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 • 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 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).

  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 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

  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…?

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