Hall A Collaboration meeting January 5th 2007 A. Camsonne

Compton Polarimeter StatusReport

Alexandre CamsonneHall A Collaboration Meeting

January 4th 2007

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Status in 2006

• Not very big year for Compton since most running was low energy

•Data taken at 2 GeV

•Gen

•He4 polarisation ( test data )

•Current status

•Problem with electron detector seems to have been damaged

•Upgrade developments on going to allow low energy running and better systematics

Hall A Collaboration meeting January 5th 2007 A. Camsonne

The Hall A 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, Duke

Scope:

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Expected Performance

Simulation byDavid Lhuillier

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

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Optical Setup

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

Hall A Collaboration meeting January 5th 2007 A. Camsonne

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

Hall A Collaboration meeting January 5th 2007 A. Camsonne

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.

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Assembled Cavity

Photograh: Alan Gavalya

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Cavity Mirror Mount

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Optics Summary• Laser

• The Prometheus laser lost power dramatically and developed large intensity noise within a few moths of operation• Sent back to Innolight, Germany for repairs. 2 month down time and 9K$• After repairs (replacing the pump diodes and realignment) the power is back to over 100 mW exceeding

specification.• However, Botao’s profiling finds that the beam is still 70% elliptic. We will try to solve it with optical circularization.• Intensity noise suppression electronics now installed on the laser. 4k$• Polarization transfer function has been fully characterized (Xiaochao)• Mode matching solution developed (Alex Jousse and Botao Jia)

• Alignment• Cavity mirror alignment with red HeNe laser works nicely• High resolution motorized mirror alignment and beam steering implemented (David

Jacobs) EPICS interface under way (Sue Witherspoon)• Position sensitive photo-detectors installed

• Cavity• The cavity is mechanically stable and responsive to mirror alignment ( Joyce and Ravi)• In 10-8 Torr vacuum (Greg Marble and Ed Folts)• The cavity demonstrates strong TEM00 resonance• However, laser-to-cavity coupling is poor (30%) -> improve mode matching

Hall A Collaboration meeting January 5th 2007 A. Camsonne

New Electron Detector

• Electron Detector (Bernard Michel)• MOU with LPC Clermont-Ferrand• LPC takes responsibility for a new high resolution electron detector• 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 (ETROC)• New DAQ and Analysis Software

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Electron Detector Status

• Silicon Microstrips (Michel Brossard)

• Silicon microsrtip final design completed • Four planes have been ordered from Canberra-Eurisys system• Delivery of first plane expected late December

• Mechanical (Francois Daudon, Alan Gavalya, Joyce Miller, Chris Curtis)

• Vacuum chamber final design completed, fabrication to begin soon• Survey and alignment scheme finalized • Vertical motion system design in progress• Installation plan in development with AES (Tim Whitlatch)

• DAQ/Analysis (Alex Camsonne)

• Working on CODA interface for new ETROC• Need new electron event analyzer

• Control System (Sue Witherspoon)

• Motion Control EPICS interface• Beam shut-down safety interlock

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Silicon Microstrip Plane

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Electron Detector Assembly Drawing

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Silicon Microstrip Mount

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Compton photon integrating method

• A couple of shifts dedicated to the Compton tune during E03-104 ( Special thanks to S. Strauch and R. Ent )

• Test Flash ADC integrating method• Beam tuning to get a reasonable signal over background ratio• First test with DC coupled base for the PMT of the central crystal• Commissionning of the Flash ADC• Production data ( invasive because of bad injector tune)

Low current running

First Compton events in FADC

Hall A Collaboration meeting January 5th 2007 A. Camsonne

PMTFan in/outAmplifier

Upstairs counting house

Experimental hall

FADCAmplifier

Setup

New base

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Signal from Flash ADC

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Signal from Flash ADC

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Compton events

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Compton signal

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Compton signal

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Measurement principle

• Compton asymmetry ?

Hall A Collaboration meeting January 5th 2007 A. Camsonne

Concluding Remarks

The Hall A Green Compton Polarimeter Upgrade Project is on track to be operational in 2008

- Issues and concerns:

The Prometheus laser’s short lifetime is a concern

Alternative single pass PPLN based green laser is important backup to be studied

Coupling efficiency of the laser to the cavity is rather low at 20%.

More work is needed to improve coupling efficiency.

Locking servo electronics needs more effort and interaction with the manufacturer. An electronics engineer/student is needed.

- On going developments for 2007 :

Electron detector

Cavity

Photon detector integrating method