The BoNuS Detector A Radial-Drift GEM TPC Howard Fenker TPC R&D Meeting LBL, March 24, 2005
Jan 19, 2016
The BoNuS Detector
A Radial-Drift GEM TPC
Howard Fenker TPC R&D MeetingLBL, March 24, 2005
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
Motivation
• Purpose– Provide almost-free
neutron target to improve our understanding of neutron structure.
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
Spectator Proton Characteristics
• Angular distribution is isotropic. Backwards proton almost certain to be a spectator.
• Momentum distribution favors low values.
Relative Ionization Yields
Spectator tracks are 20x - 50x minimum ionizing.
-> Detector can be made almost insensitive to lighter particles.
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
Optical properties of the CEBAF beam allow the use of a very narrow target.
Spectator protons can escape the target and be detected.
Conventional TPC
Advantages for BoNuS:•Cylindrical•Very low mass. •Most energy dE/dx is in sensitive materials.•Many measurements of each track.
Conventional TPC Radial
TPC
•Shorter drift path.•Tolerates non-uniform B-field.
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”
From “A Comparative Study of GEM Foils from Different Manufacturers”, Bob Azmoun (BNL), G. Karagiorgi(FIT), C. Woody (BNL)
Long-term: Gain Drift
Rate Dependence of Gain
• 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
100 MeV/c pion 100 MeV/c proton
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
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
Drift Region Cathode
Field Cage Electrodes
GEM HV Connections
(GEMs and Readout Board are not shown)
ULTEM® Frame Parts
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.
LOCAL FIELD DEFORMATION NEAR CURVED GEM IS NEGLIGIBLE
…and Curved GEMs do work.
Operation of a Curved-GEM Radial TPC, at least with the modest resolution requirements of BoNuS, has been successful.
The challenge is construction.
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
ALICE and BoNuS Readout System
BoNuS Carrier Card
ALICE FECALICE RCU
RibbonsToRTPC
pRTPC w/ Inverter/Driver Cards
RibbonsToReadoutSystem
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
• 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
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!