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Hall A Compton Polarimeter Upgrade. Sirish Nanda Jefferson Laboratory PRex Collboration Meeting July 28, 2006. Compton Polarimeter Upgrade. Motivation:.
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Hall A Compton Polarimeter Upgrade Sirish Nanda Jefferson Laboratory PRex Collboration Meeting July 28, 2006
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 Scope: • New Electron Detector • High resolution silicon microstrips to improve tracking resolution Integrating Photon Detector Improve systematic uncertainties experienced in the counting method 1.5kW Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavity Four-fold increase in Figure-of-Merit Participating Institutions:Jefferson Lab, Saclay, Syracuse, Clermont-Ferrand, UVa
Expected Performance Simulation by David Lhuillier < 1% error @0.85 GeV obtained in about 4 hrs with 50 uA beam
Optical Setup • Laser frequency is continuosly tuned to lock to Fabry-Perot Cavity
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
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
Green Fabry-Perot Cavity • 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. • Fixed mirror distance • 2 Axis adjustable mirror mount • 2 Axis adjustable stands • UHV compatible
Fabry-Perot basics • Wave equation looks like harmonic oscillator: • Solutions for x and y are Hermite-Gauss polynomials • Longutunal Modes • Transverse Mode
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 • TEM00 Resonance observed at every 3.5s Transmission Photodiode signal Frequency Ramp Finesse Measurement F=FSR/dn <Finesse> 54524 + 10504 Meets requirement
Transverse Modes of the Cavity Setup Injection Power 20mW Thermal Frequency Scan With 20 mHz 80 mV TEC voltage ramp Imager: Spiricon LBA camera • Strong TEM00 modes • However, many high order modes…
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
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.
Prometheus Beam Profile (Jousse) Not 100% TEM00, significant ellipticity
Motorized Mirror Control (Jacobs) LabView Interface to Newfocus Picomotor Drives Note: this is the motion System in the final cavity
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 mm pitch silicon mstrips • 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)
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
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
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.