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Prototypes of high rate MRPC for CBM TOF

Prototypes of high rate MRPC for CBM TOF. Jingbo Wang Department of Engineering Physics, Tsinghua University, Beijing, China. RPC-2010-Darmstadt, Germany. Outline. CBM TOF requirement Low resistive silicate glass Pad readout MRPCs Chamber Structure Test setup Test results

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Prototypes of high rate MRPC for CBM TOF

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  1. Prototypes of high rate MRPC for CBM TOF Jingbo Wang Department of Engineering Physics, Tsinghua University, Beijing, China RPC-2010-Darmstadt, Germany

  2. Outline • CBM TOF requirement • Low resistive silicate glass • Pad readout MRPCs • Chamber Structure • Test setup • Test results • Strip readout MRPCs • Chamber Structure • Test setup • Test results • A prototype for CBM TOF

  3. 1. CBM TOF requirement • Overall time resolution σT = 80 ps. • Space resolution ≤ 5 mm × 5 mm. • Efficiency > 95 %. • Pile-up < 5%. • Rate capability > 20 kHz/cm2. • Multi-hit capability (low cross-talk). • Compact and low consuming electronics (~65.000 electronic channels). 20 kHz/cm2

  4. 2. Low resistive silicate glass 3-4×1010Ωcm • The accumulated charge was 1 C/cm2, roughly corresponding to the CBM life-time over 5 year operation at the maximum counting rate. T = 28 C° HV = 1kV • Using electrodes made of semi-conductive glass is an innovative way of improving the rate capability of Resistive Plate Chambers.

  5. 3. Pad readout MRPCs • Chamber structure • Test setup • HV scan • Rate scan

  6. Structure: MRPC#1_6-gap • Parameters • Gap number: 6 • Glass type: silicate • Gap width: 0.22mm • Glass thickness: 0.7mm • Gas mixture: Freon/iso-butane/SF6 96.5%/3%/0.5% Low-resistive silicate glass with a bulk resistivity of 3~4×1010Ωcm Almost the same as the standard STAR module 63mm

  7. Structure: MRPC#2_10-gap Positive HV Negative HV 30mm 31.5mm • MRPC#2 has a similar structure and working conditions than MRPC#1 but with different dimensions of the pick-up pads. • Such a structure provides higher signal amplitudes and smaller fluctuations, which are expected to improve the detection efficiency as well as the time resolution.

  8. Test setup • Tests were performed at GSI-Darmstadt under uniform irradiation by secondary particles stemming from proton reactions at 2.5 GeV. • The higher rates can be obtained by moving the RPCs up closer to the main beam. 2.5GeV

  9. Counting rate • PMT rate: 0.8~20 kHz/cm2 • MRPC rate: 2~30 kHz/cm2 • Mean rate: 1.4~25 kHz/cm2 Top View • The beam comes in spills. • We take the mean of the PMT and MRPC measurements as a sound reference for rate estimates .

  10. Time difference Timediff =TMRPC#1-TMRPC#2

  11. Charge distribution of MRPC#2 MRPC#2: 10-gap • With rate increasing, the average charge decreases, which leads to a relativity lower efficiency.

  12. HV scan at 800Hz/cm2 • The efficiency reaches above 90% and the time resolution remains below 90ps once at the efficiency plateau. • By means of using more gas gaps, the 10-gap RPC shows a better performance. MRPC#1: 6-gap MRPC#2: 10-gap

  13. Rate scan 90% 110ps 76% 85ps • The efficiencies and time resolutions deteriorate with the counting rate. • MRPC#2 yields much better results: 90% efficiency, 85ps resolution. MRPC#1: 6-gap MRPC#2: 10-gap

  14. 4. Strip readout MRPCs • Chamber structure • MRPC#3: silicate glass • MRPC#4: common glass • Test setup • HV scan • Position scan • Analysis with particle tracking

  15. Structure: MRPC#3 & MRPC#4 • Glass type: silicate / common • HV electrode: colloidal graphite • Number of gaps: 10 • Gap width: 0.25mm • Glass thickness: 0.7mm • Gas mixture: Freon/iso-butane/SF6 96.5%/3%/0.5% colloidal graphite Guarding line Diameter:1.5mm Hole size:0.5mm 3mm 1.5mm 22mm 5mm 240mm Width:0.508mm Top and bottom layers

  16. Test Setup • MRPC#3：silicate glass • MRPC#4: common glass Target Tsinghua RPC Silicon Main beam PM12 PM5 PM34  10 m

  17. HV scan Tdiff =T MRPC#3-T MRPC#4 , σMRPC#3 ≈ σMRPC#4 ≈ σdiff /sqrt(2)

  18. "or" eff 100 strip1 strip2 80 strip3 "and" eff 60 Efficiency(%) 40 20 0 -20 -10 0 10 20 30 40 Rpcy(mm) Position Scan MRPC#3 3 2 1 Rpcy MRPC#4

  19. Position resolution T1 T2 DeltaT=(T2-T1)/2 • Using the tracking, we get the signal propagation velocity: ~ 54ps/cm • Position resolution: ~ 1 cm

  20. Efficiency correction with tracking 2×4 (cm2) 1×2 (cm2) MRPC#3 MRPC#4 Efficiency: 95% 97%

  21. Crosstalk: MRPC#3_silicate Rpcy (cm) Crosstalk_1=counts(T2>0 && T1>0) / counts(trigger) 3 2 1 10% 20%

  22. Crosstalk: MRPC#4_common Rpcy (cm) Crosstalk_1=counts(T2>0 && T1>0) / counts(trigger) 3 2 1 2% 2%

  23. 5. A prototype for CBM TOF • Chamber structure • Cosmic ray test system • HV scan

  24. Structure: MRPC#5 • Glass type: silicate • HV electrode: graphite • Number of gaps: 10 • Gap width: 0.25 mm • Glass thickness: 0.7 mm • Pad dimension: 2*2 cm2 • Gas mixture: Freon/iso-butane/SF6 96%/3%/1% 2 cm 2 cm For the inner region of the CBM TOF wall 13 cm

  25. Cosmic ray test Cosmic ray

  26. HV scan 96% ~75ps • Beam test is needed!

  27. Summary • CBM TOF requirement: 20kHz/cm2 • Low resistive silicate glass: 3-4×1010Ωcm • MRPC#2: 10-gap, pad readout, silicate glass • HV scan at 800 Hz/cm2 Efficiency>95%, Time resolution: <70ps • Rate capability: 25 kHz/cm2 Efficiency: ~90%, Time resolution: ~85ps • MRPC#3: 10-gap, strip readout, silicate glass • Efficiency: ~97%, • Time resolution: ~75ps • Crosstalk: 20%, 10%? (further study is needed) • MRPC#5: 10-gap, 12 pads, silicate glass • Efficiency: ~96%, • Time resolution: ~75ps • Beam test is needed in the future!

  28. THE END!

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