Hall A Compton Polarimeter Sirish Nanda Jefferson Laboratory
Hall A Compton Polarimeter Sirish Nanda Jefferson Laboratory Hall A Collboration Meeting December 5, 2005 Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 1
The Hall A Compton Polarimeter Upgrade Motivation: Improve accuracy of experiments by providing 1% beam polarimetery down to 1 Ge. V. 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 3 k. W 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? Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 2
Upgrade Specification Comparison of present and future Compton Parameters Present Upgrade Wavelength (nm) 1064 532 Intra-cavity power (W) 1500 3000 Luminosity @50μA(μ b. s)-1 0. 26 FOM (σ. A 2) @0. 85 Ge. V 0. 57 2. 2 Energy Range (Ge. V) 2 - 6 0. 8 – 6 4 -5%? ? 1% δPe/pe @0. 85 Ge. V Doubling Frequency + Improvements to Electron Detector, Photon Calorimeter, Photon Integrating method Four-fold enhancement of F. O. M 1% absolute accuracy of beam polarization measurements at 0. 85 Ge. V Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 3
Expected Performance Simulation by David Lhuillier < 1% error @0. 85 Ge. V obtained in about 4 hrs with 50 u. A beam Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 4
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 (~k. Hz) 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… Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 5
Compton Needs a Green Cavity… • Diode Pumped Solid State (DPSS) green lasers are frequency doubled Nd: YAG IR • The primary 1064 nm 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 Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 6
The Prometheus Green Laser Manufacturer: Innolight Gmb. H, Germany • 708 nm Pump Diodes (2) • 1064 nm Nd: YAG • 532 nm SHG via PPKTP 1064 nm @2 W 532 nm @ 0. 1 W Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 7
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 Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 8
Green Optics setup in 3 He tgt lab Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 9
Alignment Method HR mirror alignment With a red laser Works nicely! Then align the green Beam to follow the Red beams path Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 10
First Resonances in Cavity Prototype Hunting for Resonance… • Tunable laser Slow thermal mode • Tuning Coefficient -6 GHz/K • External ramp voltage 5 m. Hz, 210 m. VPP • Laser temperature varied 23. 88 C to 24. 09 C • Resonance observed at every 6. 7 s Finesse Measurement F=FSR/dn Sample No. Photodiode Frequency Ramp Finesse 1 54682+286 2 66627+240 3 59493+199 4 41238+178 5 36598+155 6 53915+141 7 69070+333 8 55475+254 9 53619+145 <Finesse> 54524 + 10504 Meets requirement Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 11
Compton Research Lab • Finally we have our much cherished Lab in the ARC buliding, Rooms L 310/312! (thanks to Dennis, Kees, ODU et. al. ) October 5, 2005 Our new Lab! yay Let’s go inside… Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 12
The Lab Status • Special thanks to: • Xiao. Chao, 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 Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 13
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 Pb. WO calorimeter with a single crystal • The Pb. Wo 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 Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 14
Green Compton Schedule Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 15
Summary The Hall A Green Compton Polarimeter Upgrade Project is on track to be operational in 2008 But needs manpower. Anyone interested, contact me Thomas Jefferson National Accelerator Facility S. Nanda, December 5, 2005 16
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