Transcript Hall A Compton Polarimeter Sirish Nanda Jefferson Laboratory Hall A Collboration Meeting

Hall A Compton Polarimeter
Sirish Nanda
Jefferson Laboratory
Hall A Collboration Meeting
December 5, 2005
Thomas Jefferson National Accelerator Facility
S. Nanda, December 5, 2005 1
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?
Thomas Jefferson National Accelerator Facility
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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 @50μA(μ b.s)-1
0.26
0.26
FOM (σ.A2) @0.85GeV
0.57
2.2
Energy Range (GeV)
2- 6
0.8 – 6
4-5%??
1%
δPe/pe @0.85GeV
Doubling Frequency
+ Improvements to
Electron Detector,
Photon Calorimeter,
Photon Integrating method
Four-fold enhancement of
F.O.M   A2   k 2  E 2
1% absolute accuracy
of beam polarization
measurements at 0.85GeV
Thomas Jefferson National Accelerator Facility
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Expected Performance
Simulation by
David Lhuillier
< 1% error @0.85 GeV
obtained in about
4 hrs with 50 uA beam
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Challenge of a Green FP Cavity
• What’s the big deal?
• Can’t we just scale our Saclay IR cavity to green?
Not so easily 
• High Q cavities typically have fixed mirrors. They use the Pound-DreverHall 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 Nd:YAG 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 Nd:YAG 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 Nd:YAG
• 532 nm SHG via PPKTP
1064 nm
@2W
532 nm
@ 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 @532 super mirrors (REO)
• Reflectivity > 99.9937 %
• Finesse
> 50,000
• Loss
< 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
Thomas Jefferson National Accelerator Facility
S. Nanda, December 5, 2005 10
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
Finesse Measurement F=FSR/dn
Sample No.
Photodiode
Frequency
Ramp
Finesse
1
54682+286
2
66627+240
3
59493+199
4
41238+178
5
36598+155
<Finesse>
54524 + 10504
6
53915+141
Meets requirement
7
69070+333
8
55475+254
9
53619+145
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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 Let’s 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:
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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 => 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 YAP:Ce as a possibility
• Electron Detector (Bernard Michelle?)
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192 ch 600 mm pitch silicon mstrips -> 800 ch 250 mm pitch
Horizontal motion
-> Vertical motion
New custom FPGA trigger module, new acq. software. It’s 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
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