Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 1

Hall A Compton Polarimeter Upgrade

Sirish Nanda Jefferson Laboratory

PRex Collboration Meeting July 28, 2006

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 2

Compton Polarimeter Upgrade

Motivation:

1.5kW Green Fabry-Perot Cavity Twice the Analyzing power of present IR cavityFour-fold increase in Figure-of-Merit

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 tracking resolution

Integrating Photon Detector Improve systematic uncertainties experienced in the counting method

Participating Institutions: Jefferson Lab, Saclay, Syracuse, Clermont-Ferrand, UVa

Scope:

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 3

Expected Performance

Simulation byDavid Lhuillier

< 1% error @0.85 GeVobtained in about 4 hrs with 50 uA beam

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 4

Optical Setup

• Laser frequency is continuosly tuned to lock to Fabry-Perot Cavity

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 5

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

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 6

The Compton Team

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 7

Prometheus Green Laser

1064 nm@ 2 W

532 nm@ 0.1 W

Manufacturer: Innolight GmbH, Germany

• 708 nm Pump Diodes (2)• 1064 nm Nd:YAG• 532 nm SHG via PPKTP

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 8

Green Fabry-Perot Cavity

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

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.

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 9

Production Cavity

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 10

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

02 22

2

2

2

2

2

2

=⎟⎟⎠

⎞⎜⎜⎝

⎛−⎟

⎠

⎞⎜⎝

⎛+∂∂

+∂∂

+⎟⎟⎠

⎞⎜⎜⎝

⎛

∂∂

+∂∂

Ekcn

yE

xE

zE

ikzE ω

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 12

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

TransmissionPhotodiodesignal

FrequencyRamp

Sample No. Finesse

1 54682+286

2 66627+240

3 59493+199

4 41238+178

5 36598+155

6 53915+141

7 69070+333

8 55475+254

9 53619+145

Finesse Measurement F=FSR/

<Finesse>54524 + 10504Meets requirement

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 13

QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.

Injection Power 20mW

Thermal Frequency ScanWith 20 mHz80 mV TEC voltage ramp

Imager:Spiricon LBA camera

Transverse Modes of the Cavity

•Strong TEM00 modes•However, many high order modes…

Setup

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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

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 15

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.

Thomas Jefferson National Accelerator FacilityS. Nanda, July 28, 2006 16

Prometheus Beam Profile (Jousse)

Not 100% TEM00, significant ellipticity

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Motorized Mirror Control (Jacobs)

LabView Interface toNewfocus 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 m pitch silicon strips• 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.