Transcript Nanda_ComptonStatus - Hall A

Hall A Compton Polarimeter Upgrade
Sirish Nanda
Jefferson Laboratory
PRex Collboration Meeting
July 28, 2006
Thomas Jefferson National Accelerator Facility
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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
Scope:
New Electron Detector
High resolution silicon microstrips to
improve tracking resolution
Integrating Photon Detector
Improve systematic uncertainties
experienced in the counting method
1.5kW 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
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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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Optical Setup
•
Laser frequency is continuosly tuned to lock to Fabry-Perot Cavity
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New Compton Lab
•
Compton Polarimetry Lab
• New green laser lab (shared by Halls A & C)
• In ARC Building Rooms L310 and L312
• L310 is laser controlled area, L312 is office/control room
•
Lab Status
• Occupancy in Nov 05
• Infrastructure completed in May 06
• Cleared for Laser Safety (LSOP approval) June 06
The CPL is now fully Operational
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The Compton Team
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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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Green Fabry-Perot Cavity
Intra-cavity power
1.5 kW
The Mirrors (source Research Electo Optics)
• Dielectric HR @532 super mirrors Reflectivity > 99.9937 %
• Finesse
> 50,000
• Loss
< 20 ppm
• ROC
50 cm
Design Goal: Improve upon Saclay IR cavity non-adjustable mirror
design, while keeping mirror distance fixed.
• Fixed mirror distance
• 2 Axis adjustable mirror mount
• 2 Axis adjustable stands
• UHV compatible
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Production Cavity
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Cavity Mirror Mount
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Fabry-Perot basics
•
Wave equation looks like harmonic
oscillator:
•
Solutions for x and y are Hermite-Gauss
polynomials
•
Longutunal Modes
•
Transverse Mode
2

 2E
E   2 E  2 E   n 
 2  2ik
  2  2     k 2  E  0
 c 

z  x
y
 z


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Resonances in Prototype Cavity
Resonance Scan
•
Tunable laser 
Slow thermal mode
•
Tuning Coefficient 
-6 GHz/K
•
Injection Power 
20 mW
•
External ramp voltage 
10 mHz, 110 mVPP
•
Laser temperature varied 28.32C to 28.38C
•
TEM00 Resonance observed at every 3.5s
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Transmission
Photodiode
signal
Frequency
Ramp
Finesse Measurement F=FSR/dn
Sample No.
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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Transverse Modes of the Cavity
Setup
QuickTime™ and a
Microsoft Video 1 decompressor
are needed to see this picture.
Injection Power 20mW
Thermal Frequency Scan
With 20 mHz
80 mV TEC voltage ramp
Imager:
Spiricon LBA camera
•Strong TEM00 modes
•However, many high order modes…
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Optics Summary
•
Laser
• Laser characterization (profile, intensity, stability, noise) completed (Alex
Jousse/Xiaochao)
• Unfortunately, the prometheus laser reaches only 25% of rated power
• The beam is multi-mode and highly elliptic:( Alex is working on “beam circularization”
• The laser is to be returned to Innolight (Germany) to bring it back to factory specs => 4 6 Weeks down time.
•
Alignment
• Cavity mirror alignment with red HeNe laser works
• High resolution motorized mirror alignment and beam steering implemented (David
Jacobs)
• LabView control interface developed
•
Cavity
• Prototype Cavity demonstrates strong TEM00 resonance
• Production cavity being assembled and vacuum tested (Greg Marble)
•
PDH Lock
• Software Slow ramp frequency scan implemented (Sue Witherspoon)
• Frequency modulation tests in progress
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Prometheus Laser Power
•
We have done a complete scan of Pump Diode current, Nd:YAG temp
and PP-KTP temp
•
The best power we could achieve is around 20-30 mW.
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Prometheus Beam Profile (Jousse)
Not 100% TEM00, significant ellipticity
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Motorized Mirror Control (Jacobs)
LabView Interface to
Newfocus Picomotor
Drives
Note: this is the motion
System in the final cavity
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New Electron Detector
• Electron Detector (Bernard Michelle)
•
•
•
•
New MOU with LPC Clermont-Ferrand signed
LPC takes responsibility for a new high resolution electron detector
Will contribute 1 physicist, 1 engineer, 2 designer/techs
The new detector will be compatible with “12 GeV” machine upgrade
• Specification
• 768 ch 240 mm pitch silicon mstrips
• 4 Planes, 192 strips/plane, 1 cm spacing between planes
• 120 mm Vertical motion to allow full coverage of Compton Edge from
0.8-11 GeV
• New custom front-end, FPGA trigger module (M. Brossard)
• New DAQ Software (Alex Camsonne)
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Electron Detector Status
Detector
•
Silicon micro-strip design finalized
•
RFQ from Canberra systems for
procurement in progress
Mechanical
•
Preliminary mechanical design completed
•
Interference with photon detector being
addressed
•
Installation plan with AES in development
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Photon Detector
• Issues
• Present calorimeter is 5x5 array of PbWo crystals. Each crystal now is 2x2x23 cm. Not
have enough Mollier width to catch the whole shower in one crystal => Complicated
response function analysis.
• The crystals matrix is housed in a temp. controlled enclosure taking up precious real
estate. Temp stabilization is not used.
• New electron detector chamber interferes with present photon calorimeter
• Moving the photon calorimeter upstream by 40 cm will work for 6GeV program, but a
logistical nightmare
• For 12 GeV operation, the photon detector will move up by 10 cm. The present
calorimeter will interfere with beam line in addition to electron detector.
• New Photon Calorimeter
•
•
•
•
•
Single block with 3 or 4 Mollier radius wide and 22 rad length deep and a single PMT.
Preserve counting capabilities. Time response has to be less than 120 ns
8x8x23 cm single block PbWo in a compact enclosure and side coupled PMT
Study and conceptual design required
Integrating DAQ for improved systematic errors
• Flash ADC in lieu of analog electronics under evaluation
• Bob Michaels and Rich Holmes are working on the FADC DAQ prototype
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Compton Detectors
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Summary
The Hall A Green Compton Polarimeter Upgrade Project is on track to be
operational in early 2008
- Action Items:
Simulation to determine optimal electron detector plane separation
New compact photon detector conceptual design
Grad student participation in 2007.
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