1. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 1 Hall A Compton Polarimeter Sirish Nanda Jefferson Laboratory Hall A Collboration Meeting December 5, 2005

2. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 2 The Hall A Compton Polarimeter Upgrade Motivation: 3kW 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 track resolution Integrating Photon Detector Improve systematic uncertainties experienced in the counting method Participating Institutions: Jefferson Lab, Saclay, ANL, Syracuse, Blaise Pasacal?

3. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 3 Upgrade Specification + Improvements to Electron Detector, Photon Calorimeter, Photon Integrating method 1% absolute accuracy of beam polarization measurements at 0.85GeV Comparison of present and future Compton Parameters Doubling Frequency Four-fold enhancement of F.O.M PresentUpgrade Wavelength (nm)1064532 Intra-cavity power (W)15003000 Luminosity @50 μ A( μ b.s) -1 0.26 FOM ( σ.A 2 ) @0.85GeV 0.572.2 Energy Range (GeV)2- 6 0.8 – 6 δ P e /p e @0.85GeV4-5%??1%

4. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 4 Expected Performance Simulation by David Lhuillier < 1% error @0.85 GeV obtained in about 4 hrs with 50 uA beam

5. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 5 Challenge of a Green FP Cavity Whats the big deal? Cant 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. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 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. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 7 The 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, December 5, 2005 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. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 9 Green Optics setup in 3 He tgt lab

10. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 10 Alignment Method HR mirror alignment With a red laser Works nicely! Then align the green Beam to follow the Red beams path

11. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 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 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

12. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 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 Lets go inside…

13. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 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. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 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 m pitch silicon strips -> 800 ch 250 m pitch Horizontal motion -> Vertical motion New custom FPGA trigger module, new acq. software. Its 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 strips and software. An MOU is under negotiation

15. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 15 Green Compton Schedule

16. Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 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