Prototypes of high rate MRPC for CBM TOF

Jingbo WangDepartment 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

• Strip readout MRPCs Chamber Structure Test setup Test results

• A prototype for CBM TOF

2/27

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).

3/27

20 kHz/cm2

2. Low resistive silicate glass

4/27

0 200 400 600 800 10001E8

1E9

1E10

1E11

Applied voltage(V)

Bulk

resis

tivity(

cm

)

20°C 30°C 40°C 50°C 60°C 70°C

0 5 10 15 20 25 30 35

1

2

3

4

5

67

Current(A)

Bulk resitivity(1010cm)

Time(days)

Curr

ent(A

)

2

3

4

5

678910

Bulk

resis

tivity(1

010

cm)

• Using electrodes made of semi-conductive glass is an innovative way of improving the rate capability of Resistive Plate Chambers.

• 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

3-4×1010 Ωcm

3. Pad readout MRPCs

• Chamber structure

• Test setup

• HV scan

• Rate scan

5/27

Structure: MRPC#1_6-gap

627

63mm

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%

Almost the same as the standard STAR module

Low-resistive silicate glass with a bulk resistivity of 3~4×1010 Ωcm

Structure: MRPC#2_10-gap

7/27

30mm

31.5mm

Negative HV

Positive HV

• 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

8/27

• 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

9/27

• 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

10/27

Timediff =TMRPC#1-TMRPC#2

Charge distribution of MRPC#2

11/27

MRPC#2: 10-gap

• With rate increasing, the average charge decreases, which leads to a relativity lower efficiency.

2.3 2.4 2.5 2.6 2.7 2.870

75

80

85

90

95

100

Efficiency(%)Time resolution(ps)

Applied voltage(kV/gap)E

ffici

ency

(%)

50

60

70

80

90

100

110

120

130

140

150

Tim

e re

solu

tion(p

s)

HV scan at 800Hz/cm2

12/27

2.2 2.3 2.4 2.5 2.6 2.740

50

60

70

80

90

100

Efficiency(%) Time resolution(ps)

Applied voltage(kV/gap)

Effi

cien

cy(%

)

60

70

80

90

100

110

120

130

140

150

Tim

e re

solu

tion(p

s)

MRPC#1: 6-gap MRPC#2: 10-gap

• 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.

0 5 10 15 20 2550

60

70

80

90

100

6-gap MRPC

10-gap MRPC

Effi

cien

cy(%

)

Counting rate (kHz/cm2)

Rate scan

13/27

90%

76%

110ps

85ps

MRPC#1: 6-gap

MRPC#2: 10-gap

• The efficiencies and time resolutions deteriorate with the counting rate.

• MRPC#2 yields much better results: 90% efficiency, 85ps resolution.

0 5 10 15 20 2560

70

80

90

100

110

120

130 diff/210-gap

6-gap

Tim

e re

solu

tion(p

s)Counting rate (kHz/cm2)

4. Strip readout MRPCs

14/27

• 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

15/27

1.5mm5mm

Diameter:1.5mmHole size:0.5mm

Width:0.508mmTop and bottom layers

240mm22mm

3mm

Guarding line

• 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

Test Setup

Main beam

Target

10 m

PM12

PM34

Tsinghua RPC

PM5

Silicon

16/27

• MRPC#3 ： silicate glass

• MRPC#4: common glass

HV scan

17/27

5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.220

30

40

50

60

70

80

90

100

Eff: MRPC#3 Eff: MRPC#4

diff/2

Applied voltage(kV)

Effi

cie

ncy(%

)

60

70

80

90

100

110

120

130

140

Tim

e r

esolu

tion(p

s)

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

σMRPC#3 ≈ σMRPC#4 ≈ σdiff / sqrt(2)

Position Scan

18/27

2 3 1

Rpcy

-20 -10 0 10 20 30 400

20

40

60

80

100 "or" eff

strip1

strip2

strip3

"and" eff

Effi

cien

cy(%

)

Rpcy(mm)-20 -10 0 10 20 30

70

80

90

100

110strip1

strip2

strip3

Tim

e re

solu

tion(

ps)

Rpcy(mm)

-20 -10 0 10 20 30 400

20

40

60

80

100 "or" eff strip1 strip2 strip3 "and" eff

Effici

ency

(%)

Rpcy(mm)

MRPC#3

MRPC#4

19/27

T1 T2

DeltaT=(T2-T1)/2

Position resolution

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

~ 54ps/cm• Position resolution: ~ 1 cm

Efficiency correction with tracking

20/27

2×4 (cm2) 1×2 (cm2)

Efficiency: 95% 97%

MRPC#3 MRPC#4

5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2

40

50

60

70

80

90

100

110

Eff_tracking(%) Eff_original(%)

Effi

cien

cy (%

)

High voltage (kV)

5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2

40

50

60

70

80

90

100

110

Eff_tracking(%) Eff_original(%)

Effi

cien

cy (%

)

High voltage (kV)

-1.5 -1.0 -0.5 0.0 0.5 1.00

10

20

30

40

50

60

70

80

90

100

Cha

rge(

ch)

Efficiency_2(%)

Crosstalk_3(%)

Charge_3(ch)

Effi

cien

cy(%

)

Rpcy(cm)

0

100

200

300

400

500

600

700

800

900

1000

Crosstalk: MRPC#3_silicate

21/27

2 3 1

Rpcy (cm)

-1.5 -1.0 -0.5 0.0 0.5 1.00

10

20

30

40

50

60

70

80

90

100

Efficiency_2(%)

Crosstalk_1(%)

Charge_1(ch)

Effi

cien

cy(%

)

Rpcy(cm)

0

200

400

600

800

1000

Cha

rge(

ch)

20%

10%

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

-1.5 -1.0 -0.5 0.0 0.5 1.00

10

20

30

40

50

60

70

80

90

100

Rpcy(cm)

Cha

rge(

ch)

Effi

cien

cy(%

)

Efficiency_2(%)

Crosstalk_3(%)

Charge_3(ch)

0

200

400

600

800

1000

Crosstalk: MRPC#4_common

22/27

2 3 1

Rpcy (cm)

-1.5 -1.0 -0.5 0.0 0.5 1.00

10

20

30

40

50

60

70

80

90

100

Efficiency_2(%)

Crosstalk_1(%)

Charge_1(ch)

Cha

rge(

ch)

Effi

cien

cy(%

)

Rpcy(cm)

0

200

400

600

800

1000

2%2%

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

5. A prototype for CBM TOF

23/27

• Chamber structure

• Cosmic ray test system

• HV scan

Structure: MRPC#5

24/27

2 cm2 cm

13 cm

• 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%

For the inner region of the CBM TOF wall

Cosmic ray test

25/27

Cosmic ray

HV scan

26/27

• Beam test is needed!

96%

~75ps

Summary CBM TOF requirement: 20kHz/cm2

Low resistive silicate glass: 3-4×1010 Ωcm 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!

27/27

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