Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 1

Hall A Compton Polarimeter

Sirish Nanda Jefferson Laboratory

Hall A Collboration Meeting December 5, 2005

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 2

The Hall A Compton Polarimeter Upgrade

Motivation:

3kW 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 track resolution

Integrating Photon Detector Improve systematic uncertainties experienced in the counting method

Participating Institutions: Jefferson Lab, Saclay, ANL, Syracuse, Blaise Pasacal?

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 3

Upgrade Specification

+ Improvements to Electron Detector, Photon Calorimeter, Photon Integrating method

1% absolute accuracyof beam polarization measurements at 0.85GeV

Comparison of present and future Compton Parameters

Doubling Frequency Four-fold enhancement of F.O.M 222 EkA ×=⟩⟨σ

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

δPe/pe @0.85GeV 4-5%?? 1%

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 4

Expected Performance

Simulation byDavid Lhuillier

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

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 5

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-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 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…

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 6

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

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 7

The 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, December 5, 2005 8

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

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 9

Green Optics setup in 3He tgt lab

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 10

Alignment Method

HR mirror alignmentWith a red laserWorks nicely!

Then align the greenBeam to follow the Red beams path

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 11

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

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

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 12

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…

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 13

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

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 14

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?)• 192 ch 600 m pitch silicon strips -> 800 ch 250 m 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 strips and software. An MOU is under negotiation

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 15

Green Compton Schedule

Thomas Jefferson National Accelerator FacilityS. Nanda, December 5, 2005 16

Summary

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

But needs manpower. Anyone interested, contact me