Hall A Compton Polarimeter

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Hall A Compton Polarimeter
Sirish Nanda Jefferson
Laboratory Hall A Collboration Meeting
December 5, 2005
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The Hall A Compton Polarimeter Upgrade
Motivation
Improve accuracy of experiments by providing 1
beam polarimetery down to 1 GeV. High precision
Parity violating experiments are feasible with
this upgrade

• New Electron Detector
• High resolution silicon microstrips to improve
  track resolution

Integrating Photon Detector Improve systematic
uncertainties experienced in the counting method
3kW Green Fabry-Perot Cavity Twice the
Analyzing power of present IR cavity ?Four-fold
increase in Figure-of-Merit
Participating Institutions Jefferson Lab,
Saclay, ANL, Syracuse, Blaise Pasacal?
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Upgrade Specification
Comparison of present and future Compton
Parameters
Present Upgrade
Wavelength (nm) 1064 532
Intra-cavity power (W) 1500 3000
Luminosity _at_50µA(µ b.s)-1 0.26 0.26
FOM (s.A2) _at_0.85GeV 0.57 2.2
Energy Range (GeV) 2- 6 0.8 6
dPe/pe _at_0.85GeV 4-5?? 1
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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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Challenge of a Green FP Cavity

• Whats the big deal?
• Cant we just scale our Saclay IR cavity to
  green?
• Not so easily ?
• High Q cavities typically have fixed mirrors.
  They use the Pound-Drever-Hall fast feedback
  scheme to lock the laser to the cavity.
• PDH Locking requires a laser with narrow (kHz)
  linewidth, fast ( sub ms response) tuning and
  very fast ( MHz) frequency modulation
  capability.

Lightwave Inc developed a 1064 nm NdYAG laser
with all the above features. This laser has been
used in high Q IR Cavities by PVLAS, Virgo, LIGO,
Saclay (Hall A) and others. Similar Green laser
is not that easy
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Compton Needs a Green Cavity

• Diode Pumped Solid State (DPSS) green lasers are
  frequency doubled NdYAG IR
• The primary 1064nm IR beam is converted to 532 nm
  green via Second Harmonic Generation (SHG) with a
  non-linear crystal in a secondary cavity

SHG with a cavity ruins the linewidth and fast
feed back ability of DPSS green lasers. Such
lasers are not suitable for hi Q cavities.
There is a Solution However Recent technology
has made periodically poled non-linear crystals
possible. These are microchip wave guides that
produce SHG in single pass without the need for
fast feed back. Although low in efficiency PPKTP
preserves all the tunability and linewidth of the
seed laser
PP-KTP
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The Prometheus Green Laser

• Manufacturer Innolight GmbH, Germany
• 708 nm Pump Diodes (2)
• 1064 nm NdYAG
• 532 nm SHG via PPKTP

1064 nm _at_ 2 W
532 nm _at_ 0.1 W
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Prototype Cavity

• Fixed mirror distance
• 2 Axis adjustable mirror mount
• 2 Axis adjustable stands
• UHV compatible

• Dielectric HR _at_532 super mirrors (REO)
• Reflectivity gt 99.9937
• Finesse gt 50,000
• Loss lt 10 ppm
• ROC 50 cm

Mirror Mount Flange
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Green Optics setup in 3He tgt lab
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Alignment Method
HR mirror alignment With a red laser Works nicely!
Then align the green Beam to follow the Red
beams path
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First Resonances in Cavity Prototype

• Hunting for Resonance
• Tunable laser ? Slow thermal mode
• Tuning Coefficient ? -6 GHz/K
• External ramp voltage ? 5 mHz, 210 mVPP
• Laser temperature varied ?23.88C to 24.09C
• Resonance observed at every 6.7s

Photodiode
Frequency Ramp
Finesse Measurement FFSR/dn
Sample No. Finesse
1 54682286
2 66627240
3 59493199
4 41238178
5 36598155
6 53915141
7 69070333
8 55475254
9 53619145
ltFinessegt 54524 10504 Meets requirement
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Compton Research Lab

• Finally we have our much cherished Lab in the ARC
  buliding, Rooms L310/312! (thanks to Dennis,
  Kees, ODU et. al.)

October 5, 2005 Our new Lab! yay? Lets go
inside
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The Lab Status

• Special thanks to
• XiaoChao, Hachimi, Jack, Ed to make it all
  possible
• Status of the Lab
• Optics table installed
• Vibration isolators installed and tested
• All Compton hardware moved into the lab
• Laser safety design complete. Installation next
  week.
• Electronics and instrumentation being installed
• Vacuum system components procured. Installation
  soon
• LSOP (laser standard operation procedure) in
  preparation

We Hope to be in operation in Jan 06
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Detector Upgrade

• Photon Detector (Souder et. al.)
• Integrating DAQ for improved systematic errors
• Commissioning the integration of the Photon PMT
  signal with analog filters and amplifiers and a
  V-to-F. Gain non-linearity poses problems and
  needs to be understood.
• Flash ADC in lieu of analog electronics under
  consideration
• Replace the PbWO calorimeter with a single
  crystal
• The PbWo crystals we have now are do not have
  enough Mollier width to catch the whole shower gt
  Complicated response function analysis.
• We need 3 or 4 Mollier radius wide and 22 rad
  length deep and a single PMT.
• Preserve counting capabilities in the new photon
  calorimeter. Time response has to be less than
  120 ns to be compatible with present DAQ
• Considering YAPCe as a possibility
• Electron Detector (Bernard Michelle?)
• 192 ch 600 mm pitch silicon mstrips -gt 800 ch 250
  mm pitch
• Horizontal motion -gt
  Vertical motion
• New custom FPGA trigger module, new acq.
  software. Its a whole new detector!!
• Special thanks to Richard Jones for taking up the
  Geant simulation of the electron detector
• Currently discussing with Blaise Pascal,
  CFD to undertake the electron detector upgrade.
  They will provide 1 engineer, 2 techs, 2
  physicists, and hardware. Jlab provides the
  mstrips and software. An MOU is under negotiation

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Green Compton Schedule
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Summary

• The Hall A Green Compton Polarimeter Upgrade
  Project is on track to be operational in 2008
• But needs manpower. Anyone interested, contact me