The BoNus detector a radial-Drift gem tpc



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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 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



…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

  • 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!





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