1. Department of Engineering Physics, Tsinghua University, Beijing, China
Progress on the real-size high-rate MRPC modules & Conceptual design of the CBM-TOF wall
Jingbo Wang
Department of Engineering Physics, Tsinghua University, Beijing, China
RPC XI workshop

2. Talk Layout CBM-TOF Low resistive glass
Rate capability: proton beam test
Real-size modules: Electron beam test
Real-size modules
Electron beam
Flux estimate
Performance
Conceptual design of CBM-TOF
Summary

3. CBM FAIR
FAIR = Facility for Antiproton and Ion Research
CBM = Compressed Baryonic Matter
The CBM experiment will be operational in year 2017 at FAIR accelerator facility in Darmstadt, Germany.
CBM is designed to explore the QCD phase diagram under extremely high net-baryon densities and moderate temperatures.
The hadron identification is considered to use a time-of-flight (TOF) system based on MRPCs.
Rate capability: >20kHz/cm2

4. Low resistive glass White Light Interferometer: MicroXAM-30
50cm * 50cm
Thickness distribution
(Evaluation scale= 30cm)
micrometer caliper
Uniformity: <20 μm
Typical: 5 μm
Evaluation scale= 857μm
Surface roughness: <10 nm (peak-to-valley)

5. Specifications of the glass plate
Bulk resistivity at various positions
Long term stability test
Variation: <30%
Bulk resistivity VS HV

6. Proton beam test, GSI@April2009
PMRPC#0: First high rate module for CBM-TOF
2.5GeV
MRPC Geometry: Double-stack
Pad size: cm * 3cm
Gas gap: mm
Proton beam: GeV, Pulsed
Rate capability: kHz/cm2.
Time resolution: < 90 ps
J. Wang, et al., Nucl. Instr. and Meth. A 621 (2010) 151.

7. Two real-size modules Rate region: Region2-4
PMRPC#1
SMRPC#2
Rate region: Region2-4
Glass type: Low-resistive glass
Read out: strips
Strip size: cm * 2.2cm
Strip pitch: cm
Gas gap: mm
Active area: 24cm * 7.2cm
Rate region: Region1
Glass type: Low-resistive glass
Readout: pads
Pad size: cm * 2cm
Pad pitch: cm
Gas gap: mm
Active area: 13cm * 4.2cm
J. Wang, et al., Nucl. Instr. and Meth. A 661 (2012) 125.

8. Electron beam test HZDR/Dresten@April2011
ELBE (Electron Linac for beams with high Brilliance and low Emittance) S1 S2 S3 S4 S9
S10
RPC S6 S5
e- beam
Electron beam: 30MeV
Pulse production rate: 6.5 MHz
Trigger: S1^S2^S3^S4^S6^RF
Typical beam size scanned by S5
Reference time from ELBE linac: σRF = 35 ps
CAEN TDC 1290 N: 24.5 ps/bin
QDC: V965: 25 fc/bin
Beam profile scanned with S5
σ = 1.1cm
σ = 1.5cm

9. Non-uniform Beam profile:
Spatial resolution:
5mm – 10mm
σx = 1.1 cm
From Scintillator5
Assumption1. Identical multiple scattering
Extrapolated by assuming identical multiple scattering in x and y directions.
σx = 1.4 cm
σy = 1.5 cm
From the strip time difference
σx = 2.15 cm
σy = 2.38 cm S1 S2 S3 S4 S9
S10
e- beam S6 S5
Along the strip
Across the strip
We could believe that the multiple scattering is the main reason for the broader profile on the RPC plane. In this report, we use the profile from the time difference between both ends of the strip.

10. 2-D beam profile
Assumption2. The beam profiles in horizontal(x) and vertical(y) directions are independent
X [cm]
Y [cm]
Φ[kHz/cm2]
Flux over the central strip
Profile from RPC:
X [cm]
Φ[kHz/cm2]
Y [cm]
X [cm]
Φ[kHz/cm2]
Flux vs x-Position

11. Description by DC model: Conversion from Qfast to Qtot
The fast charge (Qfast) is recorded by the QDC.
The total charge (Qtot ) is defined by Qtot=I/r. I is the current pushed by the HV supply and r is the particle rate.
At low fluxes (HV scan), the experimental correlation between Qtot and Qfast can be descriped by a polynomial function.
At high fluxes, Qtot can be obtained from Qfast with a simple conversion.
Qfast vs x-Position
Qtot vs Qfastc
Qtot vs x-Position

12. Description by DC model: Qtot vs ϕRPC
Qtot vs x-Position
Qtot [pC]
Qtot vs ϕRPC
X [cm]
Qtot [pC]
X [cm]
Φ[kHz/cm2]
Flux vs x-Position
Description by DC model
Φ[kHz/cm2]
The behavior of the RPC just depends on the localized flux

13. Average flux under non-uniform irradiation
Option1: FWHM
Option2: Mathematical expectation
Under non-uniform irradiation, the flux calculation is sensitive to the effective irradiation area (A*).
Mathematical expectation is an appropriate estimate for our test condition.
For a finite detector, one should set integration boundaries and normalize the probability density function.
X [cm]
Φ[kHz/cm2]
Y [cm]
a factor of >2

14. All performances vs Average flux
Under non-uniform irradiation, the average flux is defined as the mathematical expectation.
The results from the two beam tests are consistent.
The working HV of the strip counter is not optimized and the performance could be improved.
Rate capability: kHz/cm2
CBM requirement

15. Rate capability VS Bulk resistivity

16. Current conceptual design of CBM-TOF
Timing RPC with:
wall area: A = 150 m2
intrinsic time resolution: sT ~ 50 ps
rate capability: R ~ 0.5 – 25 kHz/cm2
granularity: DA ~ 4 – 30 cm2
operation mode: free running 4 3 2 1
Rate profile (Au-Au(minimum bias) at E=25 GeV/A)
Rate profile (Au-Au(minimum bias) at E=25 GeV/A) 1
kHz/cm2, #SM: 8 (low resistive glass/ceramic) 2
kHz/cm2, #SM: 12 (low resistive glass)
A. Kiseleva, P.-A. Loizeau 3
kHz/cm2, #SM: 16 (low resistive glass) 4
kHz/cm2, #SM: 44 (float glass, warming up)
Low resistive glass
I. Deppner, et al., Nucl. Instr. and Meth. A (2010), doi: /j.nima

17. Detector family for the CBM-TOF
Its very inspiring that the appropriate MRPC prototypes have been already tested with high intensity beam and the performance can fulfill the CBM requirements.
Based on the small structure modification, we design a high rate detector family and propose to construct the whole TOF wall with this type of counters.
modules for Region3 and Region4
module for Region1
modules for Region2

18. Assembly design of the Super Module
Rate profile (Au-Au(minimum bias) at E=25 GeV/A)
Rate profile (Au-Au(minimum bias) at E=25 GeV/A) 4 3 2 1
SM for Region1
SM for Region2
SM for Region3 and Region4

19. Summary Low-resistive glass: ~1010 Ωcm Proton beam test, GSI@April2009
Performance of High rate MRPC
Low-resistive glass: ~1010 Ωcm
Proton beam test,
Rate capability: 25 kHz/cm2
Electron beam test,
Rate capability: kHz/cm2
Fullfill the CBM requirement(20 kHz/cm2)
Flux estimate
Beam profile obtained from RPC time difference under self-trigger
Average flux estimated with mathematical expectation
Conceptual design of CBM-TOF
Based on low-resistive glass MRPCs
Small structure modification

20. Thanks for your attention
Contributing institutions:
Tsinghua Beijing,
NIPNE Bucharest,
LIP Coimbra,
GSI Darmstadt,
USTC Hefei,
PI Heidelberg,
KIP Heidelberg,
INR Moscow,
ITEP Moscow,
IHEP Protvino,
FZD Rossendorf,
KU Seoul,
RBI Zagreb.