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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 - PowerPoint PPT Presentation
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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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