The BoNuS Detector A Radial-Drift GEM TPC Howard Fenker TPC R&D Meeting LBL, 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. 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 p spectator 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 pion100 MeV/c proton

Cosmic TracksProton 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 FEC ALICE RCU Ribbons To RTPC

pRTPC w/ Inverter/Driver Cards Ribbons To Readout System

Detector System Tests Readout –128 channel tests –Analog Electronics Prototype test results. –Software –Straight tracks –dE/dx…

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 R HIT vs. Time Bin (V drift varies with R) Curved e - Drift N.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!