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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