Electron Detector for theHall C Compton

PolarimeterJ.W. Martin & D. Dutta

U. Winnipeg & Mississippi State U

Tasks List from Previous Meeting

• Decide technology ASAP– Base decision on:

• rates (signal and background)• granularity (guess similar to Hall A and Mainz?)• fiducializability?

– Current favorite: …? Input from collaboration/experts?

• Begin detailed budgeting for upcoming grant cycles– NSERC: deadline end of Oct.– DOE: deadline Nov.– Need ideas on how to split tasks (MSU vs.

UWpg/Canadians)• Detailed simulations – decide position wrt chicane

dipoles.• Prototyping• Receive funding• Build it

7/25/06

Technology Selected: CVD Diamond Strip

Detector • Lets examine

why?Silicon Diamond

Band Gap (eV) 1.12 5.45

Electron/Hole mobility (cm2/Vs)

1450/500 2200/1600

Saturation velocity (cm/s) 0.8x107 2x107

Breakdown field (V/m) 3x105 2.2x107

Dielectric Constant 11.9 5.7

Displacement energy (eV) 13-20 43

e-h creation energy (eV) 3.6 13

Av. e-h pairs per MIP per micron

89 36

Charge collection distance (micron)

full ~250

Low leakage current, shot noise

Fast signalcollection

Low capacitance, noise

Radiation hardness

Smaller signal

Thanks R. Wallny (UCLA)

Technology Selected: CVD Diamond Strip

Detector Operation of Diamond Detectors•~250 V bias voltage for 250 micron det. (1V/micron)• Charged particle generates e-h pair,• Which drift apart in E-field to collectingelectrodes. • Detect the charge pulses (AC-coupled detectors): Fast, low noise• Or measure induced current (DC-couples radiation sensors): ~pA noise

Charge collection in diamonds:• Signal limited by impurities and grain boundaries• Increases with E-field up to ~1V/m • Charge collection distance ~ 250 micron in poly-crystal diamonds, longer in single crystal.

Thanks H. Kagan (Ohio State)

Radiation Hardness of Diamond Detectors

Performance afterirradiation with protons

• Little change in S/N after exposure of ~5 Mrad• 15% change in S/N after an exposure of ~50 Mrad

Si 50% change in S/N after exposure of ~3 Mrad.

Thanks R. Wallny (UCLA)

A pCVD Detector is Operational at BaBar (as BLM)

Diamond detector in BaBar used to protect the Si vertex detectorThanks R. Wallny (UCLA)

A Working Diamond Strip Detector

Thanks R. Wallny (UCLA)

Current Vendors

• Element Six (UK based, subsidiary of

de Beers, S. Africa)(2.1x2.1 cm2 one of their standard sizes, most used vendor)

• Advanced Diamond Solutions ( US based)

(relatively new, supplied to LANL and NSCL (MSU), quoted the highest price)

• Sumitomo Semiconductors (Japan/US

based)

• Nasty acid bath to clean off bits.• Metallization with Ti/Au or Cr/Au, etc.• Photolithography to etch strips

– or shadow mask in metallization stage

• Fabricate carrier board• Glue detector to board• Wirebond detector strips to strips on board

From Diamond to Detector

Once this is done, we can think about reading the thing out with “standard” silicon electronics.

Lithography & Metallization Options

• U. of Manitoba (EE)complete nanofabrication laboratory, lots of experience with silicon, RF systems, board design – cost is nominal, but we must supply/train manpower.

• Ohio State Univ (Harris Kagan, HEP) part of CERN RD42 Group, original developers of the detector tech, promises to do small jobs as ours for free.

(including, wire bonding and making carrier boards)

NSFL director Cyrus Shafai giving tour to UWinnipeg students Dec. 2006. (clean room seen behind)

Sample preparation (acid bath and metallization) for diamond discussed with and ok’ed by Shafai(based on Phy. Stat. Sol. paper)

Readout Electronics

• Use Hall A (French) Electronics• Custom design by TRIUMF (or build based

on French design)• LHC (ATLAS) Electronics

• Electronics chain:– Preamp– Discriminator– Fast logic/trigger generation– Digital I/O

• Result: a “strip map” on an event-by-event basis

Options

HALL-C Schematic

4 staggered Planes of 2.1x2.1 cm2 CVD diamondcrystals~250-500m thick 100-150 micron pitch.

2 planes + motion mechanism to be built by Winnipeg, U. Manitoba & TRIUMF2 planes to be build by MSU

Funding Requests

D. Dutta to DOE for $75,000 to build 2 planes

J.W. Martin et al. to NSERC for $110,000 CAD for 2 planes and motion mechanism

NSERC budget table

Strip map for Compton events 210 m strips

4th dipole

scattered electron

e- det

det

• Compton x-sect and asym found to be in working order• electron det can now move upstream of 4th dipole• plan to investigate systematic effects (backgrounds, calibration, granularity) in Geant

Progress on simulations(D. Storey, UWinnipeg undergrad)(based on work of R. Jones et al)

Status• DOE decision: March• NSERC:

– “Large projects day” Feb. 5 defend proposal at NSERC HQ in Ottawa in front of “grant selection committee”.

– April 1 decision.

• Simulations: ongoing (D. Storey senior thesis)• Prototyping: Jeff would love to start

immediately, but needs more manpower.– Peiqing Wang (UM) PhD student, but must

complete Masters thesis (toroid field mapping) before beginning on this project.