The%20Hall%20A%20Compton%20Polarimeter

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The Hall A Compton Polarimeter
Sirish Nanda Jefferson
Laboratory Hall A Collaboration Meeting
June 22, 2007
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Compton Polarimetry
s
E,E
k,k
s -
ltAthgt2
kmax340 MeV

• Figure-of-Merit s x A2 k2 x E2

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The Hall A Compton Polarimeter Upgrade
Motivation
Improve accuracy of polarization 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

New Photon Detector Improve systematic
uncertainties experienced in the counting
method While preserving counting abilities
High Power 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,
Duke,Carnegie-Mellon
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Expected Performance
Simulation by David Lhuillier lt 1 error _at_0.85
GeV obtained in about 4 hrs with 50 uA beam
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Electron Detector LPC Clermont-Ferrand
(contact B. Michel)

• Specification
• 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

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Electron Detector Assembly
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Electron Detector Status

• Detector Electronics (Michel Brossard)
• Four planes of Silicon microsrtip delivered by
  Canberra Systems
• Front-end analog electronics completed
• ETROC Trigger system in fabrication
• Test scheduled for July/Aug 07
• Fifth spare microstrip ordered from Canberra
• Mechanical (Francois Daudon)
• Detector chamber design completed and approved
• Parts in fabrication
• Vertical motion controller to be done
• DAQ (Alex Camsonne)
• CODA readout for new ETROC
• New electron event decoder
• The new detector will be compatible with old DAQ
  and Analysis with only 48 strips active Just in
  case
• Support Structure and Installation (Alan Gavalya,
  Tim Whitlach, Chris Curtis, Ed Folts)
• Survey alignment scheme finalized
• Support structure in design
• Preliminary installation plan developed

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Photon DetectorCarnegie-Mellon University
(Contact Gregg Franklin)

• Calorimeter
• Simulation and Conceptual design Completed
• Single large crystal GSO/Single PMT
• High light output, fast decay time (less than 60
  ns)
• Preserve triggered counting capabilities.
• Small sample test at CMU this summer with loaner
  from the detector group
• Crystal procurement negotiations with Hitachi in
  Progress
• Integrating DAQ
• Flash ADC prototype has been beam tested (R.
  Michaels)
• Improvements needed
• New ADCs in procurement
• Further beam tests planned for 2007/8

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Green Fabry-Perot CavityJefferson Lab and Duke
University (contact SN)

• Specification
• Intracavity power 1.5 kW
• Wavelength 532 nm
• Mode CW, TEM00
• CIP Spot size (?) 65 ?m
• Locking PDH
• Solutions
• Primary a) Tunable smart single pass Green
  Laser -gt Passive High Finesses cavity,
• Feedback to laser PZT to lock (Botao Jia)
• b) Tunable smart IR Laser single pass
  PPLN SHG -gt Passive High Finesse
• Cavity, Feedback to laser PZT (Diana Parno)
• Alternate non-tunable dumb Green Laser
  Electro-optic frequency modulator -gt Active
  low Finesse cavity. Feedback to
  cavity exit mirror PZT (Could use help)

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Optical Setup
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Setup in Compton Lab
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Assembled Cavity
Photograh Alan Gavalya
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Pound-Drever-Hall Locking Scheme
Detect phase of the resonance from reflected
light Feedback to tunable element to stay
locked to resonance
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Locking Experience
Problems Salcay PDH Electronics Did not work
with Prometheus green laser Commercial
Electronics Required substantial
modifications. Produced unstable
intermittent locks of short duration Mechanical
Cavity Input mirror showed
mechanical instability
Picomotor mount re-design solved mechanical
instability (Ravi)
For locking electronics We pursued a home brew

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Digital CavLock Prototype home-brewed approach

• ARM7 RISC 32-bit ?Processor (Analog Devices
  ADuc7026)
• 12-bit ADCs and DACs
• Fast interrupt handler
• Flash memory

• Feed-Back Servo
• Resosnace Phase detector
• PID Regulator
• Fast and Slow Error Feedback to Laser

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Host PC C Control Program via JTAG Port
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Locking with CavLock
10-sec Scope Trace

• On-demand lock within seconds
• Stable and reliable Lock for hours
• Production version to be implemented
• soon (Fernado Barbosa)

Transmission Reflection Fast
Scan Slow Search
40-min Strip Chart
20 minutes
Reflection
Transmission
Lock Command
Fast Ramp Error Signal
Slow Ramp
Unlock Command
Minutes
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Cavity Power

• We have succeeded in locking, Next is
  optimization of Cavity Power
• So, How much power do we really need?

• Must have 0.5 - 1 kW we can be in
  business with this if the beam tune
  is clean

• Should have 1 - 2 kW Our design goal
  for routine operation

• Would like to have 2 - 3 kW gives us better
  operating margin when the beam tune is
  poor

• Too Much gt 3 kW Present DAQ
  will choke at the counting rate

• Unlikely gt 5 kW Limit of
  present optics damage threshold

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PPLN SHG

• The Prometheus Green laser has some problems
• The laser may not be able provide the injection
  power we need to achieve 1.5 kW we should have in
  the cavity
• The pump diodes have short lifetime requiring
  frequent offsite service
• We are developing our own kHz linewidth tunable
  green laser by frequency doubling a Lightwave
  1064 nm IR Laser to 532 nm (Diana)
• With a PPLNMgO crystal from HC Photonics 10-15
  mW 532 nm output has been achieved with 700 mW IR
  input.

Pursuing power amplification to several hundred
milliwats with a fiber amplifier
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12-GeV Compton

• Scope
• Reduce Chicane deflection from 30 to 22 cm to
  use existing dipole magnets
• Raise FP cavity and Photon detector by 8 cm
• Vertical motion for e-detector to cover higher
  energy

e-detector
Green FP Cavity
?-detector
Raised Dipoles and Optics
Line between 6 and 12 GeV Compton Polarimeter
design and implementation effort is very fuzzy!
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Compton Upgrade Schedule

• Electron Detector
• Installation Jan-Feb 08
• Commissioning Mar-Apr 08
• Green FP Cavity
• Installation Apr-May 08
• Commissioning Jun-Jul 08
• Photon Detector
• Installation Sep 08
• Commissioning Oct 08

Production Operation 2009
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Summary

• Electron detector progress is consistent with Jan
  08 Installation
• Progress with Green FP cavity development
• Robust locking has been achieved
• Power optimization in progress
• PPLN based backup green laser solution is in
  sight
• Photon detector design proceeding well

Project progress is limited by manpower Participat
ion welcome!
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Schedule