The BoNuS Detector A Radial-Drift GEM TPC Howard Fenker TPC R&D Meeting LBL, March 24, 2005.
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Transcript of The BoNuS Detector A Radial-Drift GEM TPC Howard Fenker TPC R&D Meeting LBL, March 24, 2005.
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The BoNuS Detector
A Radial-Drift GEM TPC
Howard Fenker TPC R&D MeetingLBL, March 24, 2005
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This work was partially supported by DOE Contract No. DE-AC05-84ER40150 under which the Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility (Jefferson Lab).
Barely
Off-shell
Structure
Nucleon
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Motivation
• Purpose– Provide almost-free
neutron target to improve our understanding of neutron structure.
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Method
• Measure slow protons– Identify spectator
protons to tag e-d events in which the neutron was struck.
– Measurement of proton momentum vector tells the initial state of the neutron.
np
e
before
e
p
?
after
n
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Spectator Proton Characteristics
• Angular distribution is isotropic. Backwards proton almost certain to be a spectator.
• Momentum distribution favors low values.
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Relative Ionization Yields
Spectator tracks are 20x - 50x minimum ionizing.
-> Detector can be made almost insensitive to lighter particles.
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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.
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Big Picture
• Track secondary e- in CLAS.
• Locate e- interaction point in target.
• Link pspectator with electron vertex (need z ~8mm).
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Narrow Target
Optical properties of the CEBAF beam allow the use of a very narrow target.
Spectator protons can escape the target and be detected.
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Conventional TPC
Advantages for BoNuS:•Cylindrical•Very low mass. •Most energy dE/dx is in sensitive materials.•Many measurements of each track.
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Conventional TPC Radial
TPC
•Shorter drift path.•Tolerates non-uniform B-field.
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STAR Radial TPC
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BoNuS Detector Concept
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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
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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.
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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
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Short-term: “Charge-Up”
From “A Comparative Study of GEM Foils from Different Manufacturers”, Bob Azmoun (BNL), G. Karagiorgi(FIT), C. Woody (BNL)
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Long-term: Gain Drift
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Rate Dependence of Gain
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• 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.
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Sample Event: Proton ID by dE/dx & Curvature
100 MeV/c pion 100 MeV/c proton
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drift
xpad #
xpad #
drift
20mm x 19mm 20mm x 19mm
20mm x 19mm 20mm x 19mm
box size represents Q(x,t)
Cosmic Tracks Proton Tracks
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Production Model: Exploded View
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Production Model
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BoNuS in CLAS
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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
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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
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Prototypes
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Prototype Construction• Curved
Prototype Test Fit
Drift Region Cathode
Field Cage Electrodes
GEM HV Connections
(GEMs and Readout Board are not shown)
ULTEM® Frame Parts
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GEMs CAN be Curved
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GEMs CAN be Curved…
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Curved GEM E-Fields
• 60mm radius
• Negligible change in E-field
• Curving the GEMs should not be an issue.
LOCAL FIELD DEFORMATION NEAR CURVED GEM IS NEGLIGIBLE
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…and Curved GEMs do work.
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Operation of a Curved-GEM Radial TPC, at least with the modest resolution requirements of BoNuS, has been successful.
The challenge is construction.
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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)
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BoNuS Signal Readout System
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ALICE and BoNuS Readout System
BoNuS Carrier Card
ALICE FECALICE RCU
RibbonsToRTPC
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pRTPC w/ Inverter/Driver Cards
RibbonsToReadoutSystem
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Detector System Tests
• Readout – 128 channel tests – Analog Electronics
• Prototype test results. – Software– Straight tracks– dE/dx…
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dE/dx Analysis from TUNL
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dE/dx Analysis from TUNL
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dE/dx Analysis from TUNL
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Software/Analysis Challenges• DAQ: Interface w/CLAS data structure• Event visualization – OK and improving• Track Fitting - Straight Tracks OK and
improving
• Need to incorporate– Vdrift(R) (ongoing)– B-Field & its Non-Uniformity– Lorentz angle
RHIT vs. Time Bin(Vdrift varies with R)
Curved e- DriftN.B.: non-uniform B
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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!
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BoNuS Detector
• Much done.– Used GEMs
– Curved GEMs.
– Made TPC and RTPC.
– Developed readout.
• Plenty to do!