Hall A Compton Polarimeter

1. Hall A Compton Polarimeter Sirish Nanda Jefferson Laboratory Hall A Collboration Meeting December 5, 2005

2. The Hall A Compton Polarimeter Upgrade Motivation: 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 track resolution Integrating Photon Detector Improve systematic uncertainties experienced in the counting method 3kW Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavity Four-fold increase in Figure-of-Merit Participating Institutions:Jefferson Lab, Saclay, ANL, Syracuse, Blaise Pasacal?

3. Four-fold enhancement of F.O.M Doubling Frequency + Improvements to Electron Detector, Photon Calorimeter, Photon Integrating method 1% absolute accuracy of beam polarization measurements at 0.85GeV Upgrade Specification Comparison of present and future Compton Parameters

4. Expected Performance Simulation by David Lhuillier < 1% error @0.85 GeV obtained in about 4 hrs with 50 uA beam

5. Challenge of a Green FP Cavity • What’s the big deal? • Can’t we just scale our Saclay IR cavity to green? Not so easily  • High Q cavities typically have fixed mirrors. They use the Pound-Drever-Hall fast feedback scheme to lock the laser to the cavity. • PDH Locking requires a laser with narrow (~kHz) linewidth, fast ( sub ms response) tuning and very fast (~ MHz) frequency modulation capability. • Lightwave Inc developed a 1064 nm Nd:YAG laser with all the above features. This laser has been used in high Q IR Cavities by PVLAS, Virgo, LIGO, Saclay (Hall A) and others. Similar Green laser is not that easy…

6. Compton Needs a Green Cavity… • Diode Pumped Solid State (DPSS) green lasers are frequency doubled Nd:YAG IR • The primary 1064nm IR beam is converted to 532 nm green via Second Harmonic Generation (SHG) with a non-linear crystal in a secondary cavity SHG with a cavity ruins the linewidth and fast feed back ability of DPSS green lasers. Such lasers are not suitable for hi Q cavities. There is a Solution However… Recent technology has made periodically poled non-linear crystals possible. These are microchip wave guides that produce SHG in single pass without the need for fast feed back. Although low in efficiency PPKTP preserves all the tunability and linewidth of the seed laser PP-KTP

7. The Prometheus Green Laser • Manufacturer: Innolight GmbH, Germany • 708 nm Pump Diodes (2) • 1064 nm Nd:YAG • 532 nm SHG via PPKTP 1064 nm @ 2 W 532 nm @ 0.1 W

8. Prototype Cavity • Fixed mirror distance • 2 Axis adjustable mirror mount • 2 Axis adjustable stands • UHV compatible • Dielectric HR @532 super mirrors (REO) • Reflectivity > 99.9937 % • Finesse > 50,000 • Loss < 10 ppm • ROC 50 cm Mirror Mount Flange

9. Green Optics setup in 3He tgt lab

10. Alignment Method HR mirror alignment With a red laser Works nicely! Then align the green Beam to follow the Red beams path

11. First Resonances in Cavity Prototype Hunting for Resonance… • Tunable laser  Slow thermal mode • Tuning Coefficient  -6 GHz/K • External ramp voltage  5 mHz, 210 mVPP • Laser temperature varied 23.88C to 24.09C • Resonance observed at every 6.7s Photodiode Frequency Ramp Finesse Measurement F=FSR/dn <Finesse> 54524 + 10504 Meets requirement

12. Compton Research Lab • Finally we have our much cherished Lab in the ARC buliding, Rooms L310/312! (thanks to Dennis, Kees, ODU et. al.) October 5, 2005 Our new Lab! yay Let’s go inside…

13. The Lab Status • Special thanks to: • XiaoChao, Hachimi, Jack, Ed to make it all possible • Status of the Lab: • Optics table installed • Vibration isolators installed and tested • All Compton hardware moved into the lab • Laser safety design complete. Installation next week. • Electronics and instrumentation being installed • Vacuum system components procured. Installation soon • LSOP (laser standard operation procedure) in preparation We Hope to be in operation in Jan 06

14. Detector Upgrade • Photon Detector (Souder et. al.) • Integrating DAQ for improved systematic errors • Commissioning the integration of the Photon PMT signal with analog filters and amplifiers and a V-to-F. Gain non-linearity poses problems and needs to be understood. • Flash ADC in lieu of analog electronics under consideration • Replace the PbWO calorimeter with a single crystal • The PbWo crystals we have now are do not have enough Mollier width to catch the whole shower => Complicated response function analysis. • We need 3 or 4 Mollier radius wide and 22 rad length deep and a single PMT. • Preserve counting capabilities in the new photon calorimeter. Time response has to be less than 120 ns to be compatible with present DAQ • Considering YAP:Ce as a possibility • Electron Detector (Bernard Michelle?) • 192 ch 600 mm pitch silicon mstrips -> 800 ch 250 mm pitch • Horizontal motion -> Vertical motion • New custom FPGA trigger module, new acq. software. It’s a whole new detector!! • Special thanks to Richard Jones for taking up the Geant simulation of the electron detector Currently discussing with Blaise Pascal, CFD to undertake the electron detector upgrade. They will provide 1 engineer, 2 techs, 2 physicists, and hardware. Jlab provides the mstrips and software. An MOU is under negotiation

15. Green Compton Schedule

16. Summary The Hall A Green Compton Polarimeter Upgrade Project is on track to be operational in 2008 But needs manpower. Anyone interested, contact me