2. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 1 The Hall A Compton Polarimeter Sirish Nanda Jefferson Laboratory Hall A Collaboration Meeting June 22, 2007

3. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 2 Compton Polarimetry e-e- e-e- =2 % k max =340 MeV E,E k,k Figure-of-Merit x A 2 ~ k 2 x E 2

4. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 3 The Hall A Compton Polarimeter Upgrade Motivation: High Power Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavity Four-fold increase in Figure-of-Merit Improve accuracy of polarization experiments by providing 1% beam polarimetery down to 1 GeV. High precision Parity violating experiments are feasible with this upgrade New Electron Detector High resolution silicon microstrips to improve tracking resolution New Photon Detector Improve systematic uncertainties experienced in the counting method While preserving counting abilities Participating Institutions: Jefferson Lab, Saclay, Syracuse, Clermont-Ferrand, Uva, Duke,Carnegie-Mellon Scope:

5. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 4 Expected Performance Simulation by David Lhuillier < 1% error @0.85 GeV obtained in about 4 hrs with 50 uA beam

6. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 5 Electron Detector LPC Clermont-Ferrand (contact: B. Michel) Specification 768 ch 240 m pitch silicon strips 4 Planes, 192 strips/plane, 1 cm spacing between planes 120 mm Vertical motion to allow coverage of Compton Edge from 0.8-11 GeV New custom front-end, FPGA trigger module (ETROC) New DAQ and Analysis Software

7. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 6 Electron Detector Assembly

8. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 7 Electron Detector Status Detector & Electronics (Michel Brossard) Four planes of Silicon microsrtip delivered by Canberra Systems Front-end analog electronics completed ETROC Trigger system in fabrication Test scheduled for July/Aug 07 Fifth spare microstrip ordered from Canberra Mechanical ( Francois Daudon ) Detector chamber design completed and approved Parts in fabrication Vertical motion controller to be done DAQ ( Alex Camsonne ) CODA readout for new ETROC New electron event decoder The new detector will be compatible with old DAQ and Analysis with only 48 strips active Just in case… Support Structure and Installation ( Alan Gavalya, Tim Whitlach, Chris Curtis, Ed Folts… ) Survey alignment scheme finalized Support structure in design Preliminary installation plan developed On track for Jan-Feb 08 installation

9. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 8 Photon Detector Carnegie-Mellon University (Contact: Gregg Franklin) Calorimeter Simulation and Conceptual design Completed Single large crystal GSO/Single PMT High light output, fast decay time (less than 60 ns) Preserve triggered counting capabilities. Small sample test at CMU this summer with loaner from the detector group Crystal procurement negotiations with Hitachi in Progress Integrating DAQ Flash ADC prototype has been beam tested (R. Michaels) Improvements needed New ADCs in procurement Further beam tests planned for 2007/8

10. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 9 Green Fabry-Perot Cavity Jefferson Lab and Duke University (contact: SN) Specification Intracavity power 1.5 kW Wavelength 532 nm Mode CW, TEM 00 CIP Spot size ( ) 65 m LockingPDH Solutions Primary: a) Tunable smart single pass Green Laser -> Passive High Finesses cavity, Feedback to laser PZT to lock (Botao Jia) b) Tunable smart IR Laser + single pass PPLN SHG -> Passive High Finesse Cavity, Feedback to laser PZT (Diana Parno) Alternate: non-tunable dumb Green Laser + Electro-optic frequency modulator -> Active low Finesse cavity. Feedback to cavity exit mirror PZT (Could use help)

11. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 10 Optical Setup

12. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 11 Setup in Compton Lab

13. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 12 Assembled Cavity Photograh: Alan Gavalya

14. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 13 Pound-Drever-Hall Locking Scheme Photo detector Beam Splitter Cavity Oscillator Phase Shifter Mixer Low Pass Filter 0 Tunable Laser PID- Regulator Error signal Detect phase of the resonance from reflected light Feedback to tunable element to stay locked to resonance

15. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 14 Locking Experience Problems : Salcay PDH Electronics: Did not work with Prometheus green laser Commercial Electronics: Required substantial modifications. Produced unstable intermittent locks of short duration Mechanical: Cavity Input mirror showed mechanical instability Picomotor mount re-design solved mechanical instability (Ravi) For locking electronics We pursued a home brew…

16. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 15 Digital CavLock Prototype home-brewed approach ARM7 RISC 32-bit Processor (Analog Devices ADuc7026) 12-bit ADCs and DACs Fast interrupt handler Flash memory Host PC C ++ Control Program via JTAG Port Feed-Back Servo Resosnace Phase detector PID Regulator Fast and Slow Error Feedback to Laser 4

17. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 16 Locking with CavLock Transmission Reflection Fast Scan Slow Search Fast Ramp + Error Signal Slow Ramp Transmission Reflection Minutes 20 minutes Lock Command Unlock Command 10-sec Scope Trace 40-min Strip Chart On-demand lock within seconds Stable and reliable Lock for hours Production version to be implemented soon (Fernado Barbosa)

18. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 17 Cavity Power We have succeeded in locking, Next is optimization of Cavity Power So, How much power do we really need? Must have 0.5 - 1 kW we can be in business with this if the beam tune is clean Should have 1 - 2 kW Our design goal for routine operation Would like to have 2 - 3 kW gives us better operating margin when the beam tune is poor Too Much > 3 kW Present DAQ will choke at the counting rate Unlikely > 5 kW Limit of present optics damage threshold

19. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 18 PPLN SHG The Prometheus Green laser has some problems The laser may not be able provide the injection power we need to achieve 1.5 kW we should have in the cavity The pump diodes have short lifetime requiring frequent offsite service We are developing our own ~ kHz linewidth tunable green laser by frequency doubling a Lightwave 1064 nm IR Laser to 532 nm (Diana) With a PPLN:MgO crystal from HC Photonics 10-15 mW 532 nm output has been achieved with 700 mW IR input. Pursuing power amplification to several hundred milliwats with a fiber amplifier

20. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 19 12-GeV Compton Scope Reduce Chicane deflection from 30 to 22 cm to use existing dipole magnets Raise FP cavity and Photon detector by 8 cm Vertical motion for e-detector to cover higher energy Green FP Cavity e-detector -detector Raised Dipoles and Optics Line between 6 and 12 GeV Compton Polarimeter design and implementation effort is very fuzzy!

21. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 20 Compton Upgrade Schedule Electron Detector: Installation: Jan-Feb 08 Commissioning Mar-Apr 08 Green FP Cavity Installation: Apr-May 08 Commissioning: Jun-Jul 08 Photon Detector Installation: Sep 08 Commissioning: Oct 08 Production Operation: 2009

22. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 21 Summary Electron detector progress is consistent with Jan 08 Installation Progress with Green FP cavity development Robust locking has been achieved Power optimization in progress PPLN based backup green laser solution is in sight Photon detector design proceeding well Project progress is limited by manpower Participation welcome!

23. Thomas Jefferson National Accelerator Facility S. Nanda, June 22, 2007 22 Schedule