Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 1 The Hall A Compton Polarimeter Upgrade Sirish Nanda Jefferson Laboratory Parity

Thomas Jefferson National Accelerator FacilityS. Nanda, July 22, 2008 1

The Hall A Compton Polarimeter Upgrade

Sirish Nanda Jefferson Laboratory

Parity Collaboration Meeting July 22, 2008


The Hall A Compton Polarimeter Upgrade

Goal:

High Power Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavityIncreased in Figure-of-Merit

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

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

Duke, Carnegie-Mellon, William & Mary

Scope:


Electron Detector LPC Clermont-Ferrand

• Scope• 768 ch 240 m pitch silicon strips• 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

• 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 DetectorCarnegie-Mellon University

• Calorimeter

• Single crystal GSO, 6x15 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 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


Optical Setup


Cavity in the Compton Lab

Photograh: Alan Gavalya


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

• 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

• 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


Schedule

Aug-Sept 08Aug-Sep 08

March 09

Jan-Feb 10

2008 2009 2010

June-Aug 09


Summary

• 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

Documents

Thomas Jefferson National Accelerator Facility S. Nanda, July 22, 2008 1 The Hall A Compton Polarimeter Upgrade Sirish Nanda Jefferson Laboratory Parity