Transcript No Slide Title

The Hall A Compton Polarimeter Upgrade
Sirish Nanda
Jefferson Laboratory
Parity Collaboration Meeting
July 22, 2008
Thomas Jefferson National Accelerator Facility
S. Nanda, July 22, 2008 1
The Hall A Compton Polarimeter Upgrade
Goal:
Provide 1% beam polarimetry from 1 to 11 GeV.
High precision Parity violating experiments are feasible with this upgrade
Scope:
New Electron Detector
- High resolution silicon microstrips to
improve systematic errors
- Movable in dispersive plane for wide
energy coverage
New Photon Detector
High Power Green Fabry-Perot Cavity
Twice the Analyzing power of present IR cavity
Increased in Figure-of-Merit
- 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
Thomas Jefferson National Accelerator Facility
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Electron Detector
LPC Clermont-Ferrand
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Scope
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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
Thomas Jefferson National Accelerator Facility
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Electron Detector Plans
• Installation
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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
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Control system interface (Segal/Witherspoon) in progress
DAQ (Camsonne/Brossard) developed
• Commissioning
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First beam during Transversity Expt in Oct 08.
Pressing need: New Electron Event Analyzer!! Requires collaboration help
Thomas Jefferson National Accelerator Facility
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Photon Detector
Carnegie-Mellon University
• Calorimeter
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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
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Installation
• Installation planned for Spring 09
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Green Fabry-Perot Cavity
Jefferson Lab, Syracuse U
• Specification
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Intra-cavity power
Wavelength
Mode
CIP Spot size ()
Locking
1.5 kW
532 nm
CW, TEM00
65 mm
PDH
• Solutions
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Primary:
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Alternate: Lightwave IR laser + IPG fiber Amplifier + PPLN doubler -> Medium
Finesse Cavity
» PDH Feedback to laser
Prometheus Laser + PPLN Doubler -> High Finesse cavity
» PDH Feedback to laser for TEM00 mode lock
Thomas Jefferson National Accelerator Facility
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Optical Setup
Thomas Jefferson National Accelerator Facility
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Cavity in the Compton Lab
Photograh: Alan Gavalya
Thomas Jefferson National Accelerator Facility
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Cavity Progress
• Power
• So far we are doing <100 Watts in intra-cavity power. Need more that an
order of magnitude improvement!
• Progress
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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
Thomas Jefferson National Accelerator Facility
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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
Thomas Jefferson National Accelerator Facility
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PPLN Frequency Doubler
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Passive SHG with periodically poled (PP) Lithium Niobate (LN)
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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
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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
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Plans
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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
Thomas Jefferson National Accelerator Facility
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Schedule
2008
2009
2010
Aug-Sept 08
Aug-Sep 08
March 09
June-Aug 09
Jan-Feb 10
Thomas Jefferson National Accelerator Facility
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Summary
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Electron detector ready for Installation in Aug 08
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Photon detector development proceeding well, installation in March 09
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Progress with Green FP cavity
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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
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