1. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 1 Hall A Compton Polarimeter Upgrade Sirish Nanda Jefferson Laboratory PRex Collboration Meeting July 28, 2006

2. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 2 Compton Polarimeter Upgrade Motivation: 1.5kW Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavity Four-fold increase in Figure-of-Merit Improve accuracy of 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 Integrating Photon Detector Improve systematic uncertainties experienced in the counting method Participating Institutions: Jefferson Lab, Saclay, Syracuse, Clermont-Ferrand, UVa Scope:

3. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 3 Expected Performance Simulation by David Lhuillier < 1% error @0.85 GeV obtained in about 4 hrs with 50 uA beam

4. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 4 Optical Setup Laser frequency is continuosly tuned to lock to Fabry-Perot Cavity

5. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 5 New Compton Lab Compton Polarimetry Lab New green laser lab (shared by Halls A & C) In ARC Building Rooms L310 and L312 L310 is laser controlled area, L312 is office/control room Lab Status Occupancy in Nov 05 Infrastructure completed in May 06 Cleared for Laser Safety (LSOP approval) June 06 The CPL is now fully Operational

6. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 6 The Compton Team

7. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 7 Prometheus Green Laser 1064 nm @ 2 W 532 nm @ 0.1 W Manufacturer: Innolight GmbH, Germany 708 nm Pump Diodes (2) 1064 nm Nd:YAG 532 nm SHG via PPKTP

8. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 8 Green Fabry-Perot Cavity Fixed mirror distance 2 Axis adjustable mirror mount 2 Axis adjustable stands UHV compatible Intra-cavity power 1.5 kW The Mirrors (source Research Electo Optics) Dielectric HR @532 super mirrors Reflectivity > 99.9937 % Finesse > 50,000 Loss < 20 ppm ROC 50 cm Design Goal: Improve upon Saclay IR cavity non-adjustable mirror design, while keeping mirror distance fixed.

9. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 9 Production Cavity

10. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 10 Cavity Mirror Mount

11. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 11 Fabry-Perot basics Wave equation looks like harmonic oscillator: Solutions for x and y are Hermite-Gauss polynomials Longutunal Modes Transverse Mode

12. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 12 Resonances in Prototype Cavity Resonance Scan Tunable laser Slow thermal mode Tuning Coefficient -6 GHz/K Injection Power 20 mW External ramp voltage 10 mHz, 110 mVPP Laser temperature varied 28.32C to 28.38C TEM 00 Resonance observed at every 3.5s Transmission Photodiode signal Frequency Ramp Sample No.Finesse 154682+286 266627+240 359493+199 441238+178 536598+155 653915+141 769070+333 855475+254 953619+145 Finesse Measurement F=FSR/ 54524 + 10504 Meets requirement

13. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 13 Injection Power 20mW Thermal Frequency Scan With 20 mHz 80 mV TEC voltage ramp Imager: Spiricon LBA camera Transverse Modes of the Cavity Strong TEM00 modes However, many high order modes… Setup

14. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 14 Optics Summary Laser Laser characterization (profile, intensity, stability, noise) completed (Alex Jousse/Xiaochao) Unfortunately, the prometheus laser reaches only 25% of rated power The beam is multi-mode and highly elliptic:( Alex is working on beam circularization The laser is to be returned to Innolight (Germany) to bring it back to factory specs => 4 - 6 Weeks down time. Alignment Cavity mirror alignment with red HeNe laser works High resolution motorized mirror alignment and beam steering implemented (David Jacobs) LabView control interface developed Cavity Prototype Cavity demonstrates strong TEM00 resonance Production cavity being assembled and vacuum tested (Greg Marble) PDH Lock Software Slow ramp frequency scan implemented (Sue Witherspoon) Frequency modulation tests in progress

15. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 15 Prometheus Laser Power We have done a complete scan of Pump Diode current, Nd:YAG temp and PP-KTP temp The best power we could achieve is around 20-30 mW.

16. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 16 Prometheus Beam Profile (Jousse) Not 100% TEM 00, significant ellipticity

17. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 17 Motorized Mirror Control (Jacobs) LabView Interface to Newfocus Picomotor Drives Note: this is the motion System in the final cavity

18. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 18 New Electron Detector Electron Detector (Bernard Michelle) New MOU with LPC Clermont-Ferrand signed LPC takes responsibility for a new high resolution electron detector Will contribute 1 physicist, 1 engineer, 2 designer/techs The new detector will be compatible with 12 GeV machine upgrade Specification 768 ch 240 m pitch silicon strips 4 Planes, 192 strips/plane, 1 cm spacing between planes 120 mm Vertical motion to allow full coverage of Compton Edge from 0.8-11 GeV New custom front-end, FPGA trigger module (M. Brossard) New DAQ Software (Alex Camsonne)

19. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 19 Electron Detector Status Detector Silicon micro-strip design finalized RFQ from Canberra systems for procurement in progress Mechanical Preliminary mechanical design completed Interference with photon detector being addressed Installation plan with AES in development

20. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 20 Photon Detector Issues Present calorimeter is 5x5 array of PbWo crystals. Each crystal now is 2x2x23 cm. Not have enough Mollier width to catch the whole shower in one crystal => Complicated response function analysis. The crystals matrix is housed in a temp. controlled enclosure taking up precious real estate. Temp stabilization is not used. New electron detector chamber interferes with present photon calorimeter Moving the photon calorimeter upstream by 40 cm will work for 6GeV program, but a logistical nightmare For 12 GeV operation, the photon detector will move up by 10 cm. The present calorimeter will interfere with beam line in addition to electron detector. New Photon Calorimeter Single block with 3 or 4 Mollier radius wide and 22 rad length deep and a single PMT. Preserve counting capabilities. Time response has to be less than 120 ns 8x8x23 cm single block PbWo in a compact enclosure and side coupled PMT Study and conceptual design required Integrating DAQ for improved systematic errors Flash ADC in lieu of analog electronics under evaluation Bob Michaels and Rich Holmes are working on the FADC DAQ prototype

21. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 21 Compton Detectors

22. Thomas Jefferson National Accelerator Facility S. Nanda, July 28, 2006 22 Summary The Hall A Green Compton Polarimeter Upgrade Project is on track to be operational in early 2008 - Action Items: Simulation to determine optimal electron detector plane separation New compact photon detector conceptual design Grad student participation in 2007.