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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

Prototypes of high rate MRPC for CBM TOF

Jingbo Wang

Department of Engineering Physics, Tsinghua University, Beijing, China

RPC-2010-Darmstadt, Germany

outline
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
1 cbm tof requirement
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

2 low resistive silicate glass
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.
3 pad readout mrpcs
3. Pad readout MRPCs
  • Chamber structure
  • Test setup
  • HV scan
  • Rate scan
structure mrpc 1 6 gap
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

structure mrpc 2 10 gap
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.
test setup
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

counting rate
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 .
time difference
Time difference

Timediff =TMRPC#1-TMRPC#2

charge distribution of mrpc 2
Charge distribution of MRPC#2

MRPC#2: 10-gap

  • With rate increasing, the average charge decreases, which leads to a relativity lower efficiency.
hv scan at 800hz cm 2
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

rate scan
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

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

test setup1
Test Setup
  • MRPC#3:silicate glass
  • MRPC#4: common glass

Target

Tsinghua RPC

Silicon

Main beam

PM12

PM5

PM34

 10 m

hv scan
HV scan

Tdiff =T MRPC#3-T MRPC#4 ,

σMRPC#3 ≈ σMRPC#4 ≈ σdiff /sqrt(2)

position scan

"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

position resolution
Position resolution

T1

T2

DeltaT=(T2-T1)/2

  • Using the tracking, we get the signal propagation velocity:

~ 54ps/cm

  • Position resolution:

~ 1 cm

efficiency correction with tracking
Efficiency correction with tracking

2×4 (cm2) 1×2 (cm2)

MRPC#3

MRPC#4

Efficiency: 95% 97%

crosstalk mrpc 3 silicate
Crosstalk: MRPC#3_silicate

Rpcy (cm)

Crosstalk_1=counts(T2>0 && T1>0) / counts(trigger)

3

2

1

10%

20%

crosstalk mrpc 4 common
Crosstalk: MRPC#4_common

Rpcy (cm)

Crosstalk_1=counts(T2>0 && T1>0) / counts(trigger)

3

2

1

2%

2%

5 a prototype for cbm tof
5. A prototype for CBM TOF
  • Chamber structure
  • Cosmic ray test system
  • HV scan
structure mrpc 5
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

cosmic ray test
Cosmic ray test

Cosmic ray

hv scan1
HV scan

96%

~75ps

  • Beam test is needed!
summary
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!
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