The BoNus detector a radial-Drift gem tpc

The BoNuS Detector

• A Radial-Drift GEM TPC

Relative Ionization Yields

How to do it?

• Spectator must escape target

• Low density detector media.

• Minimal insensitive material

• Acceptance

• Large
• Symmetric about the target

• Detector sensitive to spectators, insensitive to background.

Big Picture

• Track secondary e- in CLAS.

• Locate e- interaction point in target.

• Link pspectator with electron vertex (need z ~8mm).

Narrow Target

Conventional TPC

Conventional TPC

STAR Radial TPC

BoNuS Detector Concept

Why GEM Readout?

• Uniform acceptance

• Reduced mechanical strength required

• Less massive components

• It is interesting!

• First use of GEMs at JLab
• First use of curved GEMs anywhere

Availability of GEMs

• Both CERN and 3M have produced high quality GEM foils.

• CERN’s priority is the internal program; they have limited capacity.

• 3M’s priority is Return on Investment: mass production is possible.

• Tech Etch (Plymouth, MA) applying for R&D Funding.

• We (and others) have tested both 3M and Tech-Etch GEMs.

• Tech-Etch: Have supplied working custom GEMs for the BoNuS detector.

Problems with GEMs

• Gain Uniformity

• Seen to vary ~10% over a 10cm x 10cm CERN GEM
• Study of GEM Characteristics for Application in a Micro-TPC B. Yu, V. Radeka, G. C. Smith, C. L. Woody, and N. N. Smirnoff

• Gain Stability over time

• Short term- “charge-up”
• Long term- gain drift
• Rate dependence

Short-term: “Charge-Up”

Long-term: Gain Drift

Rate Dependence of Gain

Gain variations are a potentially serious problem for dE/dx measurements

• Gain variations are a potentially serious problem for dE/dx measurements

• We are considering various calibration options

• Not so serious for tracking.

• NEVERTHELESS… we proceed.

Sample Event: Proton ID by dE/dx & Curvature

Production Model: Exploded View

Production Model

BoNuS in CLAS

Detector Parameters

• Geometric Acceptance

• Sensitive over 296 deg. In phi, 20cm in Z.

• Momentum Acceptance

• Protons from ~70 MeV/c

• Proton Identification (next slide)

• Vertex Z resolution <~ 10mm

• Track Momentum Resolution dP/P <~30%

• Track E information from dE/dx

• Rate & Timing to handle ~2000 events/s

Detector Development

• Prototype – flat, ‘standard’ GEMs

• Test

• Prototype – curved, ‘standard’ GEMs

• Test

• Prototype – flat, custom GEMs

• Test

• Production – curved, custom GEMs

• June test run in CLAS

Prototypes

Prototype Construction

• Curved Prototype Test Fit

GEMs CAN be Curved

GEMs CAN be Curved…

Curved GEM E-Fields

• 60mm radius

• Negligible change in E-field

• Curving the GEMs should not be an issue.

…and Curved GEMs do work.

Electronics Development

• Commercial CAMAC Modules – 8 ch. (5/03)

• Test the whole concept

• Cosmic / Source / TUNL Run1 (11/03)

• Milestone: choose ALTRO readout (12/03)

• ALTRO Test Board – 16 ch.

• Overcome signal polarity issue
• Cosmic / Source / TUNL Run 2 (5/04)

• ALTRO Production System – 128 ch. (12/04)

• Cosmic / Source / TUNL Run 3 (3/05)

• Final ALTRO System – 3200 ch. (6/05)

BoNuS Signal Readout System

pRTPC w/ Inverter/Driver Cards

Detector System Tests

• Readout

• 128 channel tests
• Analog Electronics

• Prototype test results.

• Software
• Straight tracks
• dE/dx…

dE/dx Analysis from TUNL

dE/dx Analysis from TUNL

dE/dx Analysis from TUNL

Software/Analysis Challenges

• DAQ: Interface w/CLAS data structure

• Event visualization – OK and improving

• Track Fitting - Straight Tracks OK and improving

Bonus Detector Outlook

• Detector Parts Delivery 4/1

• Detector Assembly 4/1 - 5/1

• Electronics Fabrication now - 5/1

• Assemble Detector, Target, Support, Readout 5/1-5/15

• Checkout: 5/15 – 5/30

• Hall-B Install & Engineering Test 5/31 – 6/8

• Physics Run October 20 – December 22,

• 2005!

BoNuS Detector

• Much done.

• Used GEMs
• Curved GEMs.
• Made TPC and RTPC.
• Developed readout.

• Plenty to do!