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The Hall A Compton Polarimeter Upgrade. Sirish Nanda Jefferson Laboratory Parity Collaboration Meeting July 22, 2008. The Hall A Compton Polarimeter Upgrade. Goal:. Provide 1% beam polarimetry from 1 to 11 GeV.

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the hall a compton polarimeter upgrade
The Hall A Compton Polarimeter Upgrade

Sirish Nanda

Jefferson Laboratory

Parity Collaboration Meeting

July 22, 2008

the hall a compton polarimeter upgrade1
The Hall A Compton Polarimeter Upgrade


Provide 1% beam polarimetry from 1 to 11 GeV.

High precision Parity violating experiments are feasible with this upgrade


  • New Electron Detector
  • - High resolution silicon microstrips to improve systematic errors
  • - Movable in dispersive plane for wide energy coverage
  • New Photon Detector
  • Large single crystal GSO calorimeter
  • Integrating FADC for improved accuracy
  • - Preserve counting abilities

High Power Green Fabry-Perot Cavity

Twice the Analyzing power of present IR cavity

Increased in Figure-of-Merit

Participating Institutions:Jefferson Lab, Saclay, Syracuse, Clermont-Ferrand, Uva,

Duke, Carnegie-Mellon, William & Mary

electron detector lpc clermont ferrand
Electron Detector LPC Clermont-Ferrand
  • Scope
    • 768 ch 240 mm pitch silicon mstrips
    • 4 Planes, 192 strips/plane, 1 cm spacing between planes
    • 120 mm Vertical motion to allow coverage of Compton edge from 0.8-11 GeV
    • New custom front-end, FPGA trigger module (ETROC)
    • New DAQ and Analysis Software

Installation in Aug-Sep 08.

Commissioning during the Transversity expt Oct 08-Jan 09

electron detector plans
Electron Detector Plans
  • Installation
    • Installation of e-detector in Aug/Sep 08
    • Mechanical design complete (Miller/Gavalya). Fabrication of parts in progress.
    • Neil Wilson (Jlab) and Francois Daudon (Clermont) heading installation activities
    • Survey and Alignment plans (Curtis) in place
  • Checkout
    • Control system interface (Segal/Witherspoon) in progress
    • DAQ (Camsonne/Brossard) developed
  • Commissioning
    • First beam during Transversity Expt in Oct 08.
    • Pressing need: New Electron Event Analyzer!! Requires collaboration help
photon detector carnegie mellon university
Photon DetectorCarnegie-Mellon University
  • Calorimeter
    • Single crystal GSO, 6fx15 cm cylinder, Single PMT
    • High light output, fast decay time (less than 60 ns)
    • Can do triggered counting as well as integration.
    • GSO Crystal procured from Hitachi, under test at CMU
    • Mechanical support/electronics in design
  • Integrating DAQ
    • Required for 1% polarimetry @1Gev
    • New Flash ADC’s beam tested in Feb 08
    • Further tests planned this fall/winter
  • Installation
    • Installation planned for Spring 09
green fabry perot cavity jefferson lab syracuse u
Green Fabry-Perot CavityJefferson Lab, Syracuse U
  • Specification
    • Intra-cavity power 1.5 kW
    • Wavelength 532 nm
    • Mode CW, TEM00
    • CIP Spot size () 65 m
    • Locking PDH
  • Solutions
    • Primary: Prometheus Laser + PPLN Doubler -> High Finesse cavity
          • PDH Feedback to laser for TEM00 mode lock
    • Alternate: Lightwave IR laser + IPG fiber Amplifier + PPLN doubler -> Medium Finesse Cavity
          • PDH Feedback to laser
cavity in the compton lab
Cavity in the Compton Lab

Photograh: Alan Gavalya

cavity progress
Cavity Progress
  • Power
    • So far we are doing <100 Watts in intra-cavity power. Need more that an order of magnitude improvement!
  • Progress
    • Laser, Optics, Mechanics well understood
    • Home made Cavlock feedback solution is successful in locking
    • On demand stable locking demonstrated at low power (Abdurahim)
    • High power locking in development
      • Cavlock production version in implementation (Dan Sexton)
      • Electronic noise issues being chased (Lawrence Lee)
  • Problems
    • Our cavity mirrors are too lossy, limiting power gain
    • Need new mirrors with < 10 ppm scatter and absorption loss.
    • Need clean-room to maintain low loss in mirrors
cavity plans
Cavity Plans
  • New Mirrors
    • We need new low loss mirrors!
    • Mirror substrates with <0.5 Angstrom surface finish ordered from General Optics Corp. Delivery in Oct/Nov
    • In talks with General Optics, Advanced Thin Flims (ATF), Research Electro Optics (REO), and Layertec for low loss mirror coatings
    • Hope to finalize mirror coating contract soon
  • Mirror Characterization
    • MOU in development with ODU to surface map high finesse mirrors to provide SEM, AFM, and Diffusion Scatter studies of mirrors.
    • Will give us quantitative measure of losses in cavity mirrors
  • Existing IR Cavity
    • Losing Power, presently at ~450 Watts
    • Plan to replace 230 mW laser with 700 mW
    • Boost power to ~1.3kW
ppln frequency doubler
PPLN Frequency Doubler
  • Passive SHG with periodically poled (PP) Lithium Niobate (LN)
    • Use IR Nd:YAG laser as 1064 nm pump
    • Double frequency with Quasi-phase matching (QPM) of non-linear crystals e.g KTP or LN
    • LN is more efficient that KTP
  • Our accomplishments with PPLN Doubling
    • QPM is sensitive to temperature
    • We have achieved temp stabilization ~ 10 mK with home made TEC temp control
    • Better than 20 mK temp uniformity along a 50 mm crystal
    • Better optical mode matching of pump IR beam

>> We have achieved >12%/W SHG conversion efficiency.

>> Demonstrated 1 watt green power with 2.9 watt IR pump

  • Plans
    • Go to higher power
    • Demonstrate locking capabilities of the PPLN Laser
    • Progress recently stalled due do lack of man power
    • Brian Han (W&M) is now ramping up the effort




Aug-Sept 08

Aug-Sep 08

March 09

June-Aug 09

Jan-Feb 10

  • Electron detector ready for Installation in Aug 08
  • Photon detector development proceeding well, installation in March 09
  • Progress with Green FP cavity
    • Robust cavity lock at low power has been achieved
    • High power lock-in in development
    • New low loss mirrors on order
    • Cleanroom infrastructure under implementation
    • PPLN laser @1 watt demonstrated. Further development necessary
  • Aiming for installation of green cavity in Winter 09