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Study on the performance of multi-gap resistive plate chambers
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430 www.elsevier.com/locate/nima
Study on the performance of multi-gap resistive plate chambers Wang Yi, Li Yuanjing, Cheng Jianping, Li Jin, Yue Qian, Lai Yongfang, Tang Le, Fu Jinhua Engineering Physics Department, Tsinghua University, Beijing 100084, China Received 3 December 2003; received in revised form 24 August 2004; accepted 17 September 2004 Available online 27 October 2004
Abstract A kind of multi-gap resistive plate chamber (MRPC) was developed for the STAR experiment at RHIC. The MRPC has excellent time resolution with high efficiency and can be used as the time-of-flight detector. In this paper, we present some performance of MRPC tested by cosmic ray, and performances of MRPC working in different gas mixture and in different temperature are also illustrated. r 2004 Elsevier B.V. All rights reserved. Keywords: MRPC; Cosmic ray; TOF
1. Introduction The multi-gap resistive plate chamber (MRPC) has good time resolution (less than 100 ps) and high detection efficiency (higher than 95%) and is a good candidate for the time-of-flight (TOF) detector for the STAR experiment at RHIC [1,2]. It is low cost and can be segmented according to requirements [3,4]. The MRPC consists of a stack of glass plates, spaced one from the other with spacers of equal thickness creating a series of gas gaps. Electrodes are connected to the outer surfaces of the two outer glass plates. A strong electric field is generated in each subgap by Corresponding
author. Tel.: +86 10 62794480; fax: +86 10 62781133. E-mail address: [email protected] (W. Yi).
applying a high voltage on the external electrodes. All the internal glass plates are left electrically floating, they take the voltage as defined by electrostatics. Typical resistivity for the glass plates is on the order of 1012–1013 O cm. The electrodes are made of resistive graphite tape and are transparent to charge. Copper pickup pads are used to read out the signals.
2. Structure of MRPC module Fig. 1 shows the structure of the MRPC module. The module consists of six pads. The size of each pad is 3.1 6.0 cm2. There is a 3 mm interval between each pad. The total active area of one module is 18.6 6.0 cm2. The glass plate is
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.09.026
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W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
Fig. 1. Structure of the MRPC module. (a) Long side view, (b) short side view.
0.52 mm thick and the resistivity is around 8 1012 O cm. There are six gas gaps of about 220 mm defined by nylon fishing-line of this diameter. The electrodes are made of a graphite tape with a surface resistivity of 7.6 105 O/square which covers the entire active area. We use a nonflammable gas mixture which contains 94.7% tetra-fluoro-ethane and 5.3% iso-butane. When a charged particle goes through the chamber the avalanche generates in the gas gaps. The induced signal on the pads is the average of possible avalanches from all gas gaps.
3. Cosmic ray test system Cosmic ray test system is used to measure the performance of MRPCs. Fig. 2 shows the diagram of the test system. The system consists of three
25 cm 5 cm 5 cm plastic scintillation counters with photo-multiplier tubes (PMTs). N415 discriminator (products of CAEN) is used for discrimination of signals from five PMTs. The coincidence signal between PMT1 and PMT5 provides the cosmic trigger for the ADC gate and the stop signal for the TDC converter. The stop time is determined by the leading edge of the pulse from PMT1. PMT1 determines the rate of accidentals and is also used to correct the efficiency accordingly. All signals from PMT2 to PMT5 are fed into a VME TDC (C.A.E.N V775, 35 ps bin width is chosen) as a start signal for digitization. The time resolution for average timing of four PMTs, (t2+t3 t4 t5)/4, is about 80 ps. The MRPC is mounted in a gas tight box flushed with the working gas, and connected to a front end electronics (FEE) card identical to those in use on the TOF (time-of-flight system based on
ARTICLE IN PRESS W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
PMT3
Scintillator 1
PMT1
Scintillator 2
PMT2
427
MRPC1 MRPC2
Scintillator 3
PMT4
PMT5
delay PMT1
Discrim 1
PMT2
Discrim 2
PMT3
Discrim 3
delay
stop
T V D PMT4
Discrim 4
PMT5
Discrim 5
C six channel TDC 6-cell MRPC
E
FEE
gate delay six channel ADC
M
A D C
Fig. 2. The block diagram of the cosmic ray test system.
MRPC technology) system. The analog and digital outputs from the FEE card are connected to the ADC (C.A.E.N V265) and TDC modules. An electrothermal wire is put in the box. The temperature of the MRPC in the box can be controlled by applying adequate voltage on the wire. The VME system connects the PC computer via an optical fiber. Labview6.0 program is used to control the ADC and TDC, read data from the ADC and TDC and display their corresponding spectrum in real time.
4. Results Ten MRPCs have been constructed and are all tested in the same condition (using the same
device, gas mixture and high voltage). Figs. 3–6 show the performance of a typical MRPC with a voltage 14 kV and with the working gas that contains 94.7% C2H2F4 and 5.3% iso-butane. Fig. 3 shows the amplitude spectrum of the MRPC. The charge per channel of V265 ADC is 0.2 pC, and the pedestal is about 250 with a gate width of 100 ns. The signals produced in the MRPC are first amplified by MAXIM3760 amplifier in FEE, and later fed into the ADC. The average charge produced in the MRPC by cosmic ray and recorded by the ADC is around 40 pC. Fig. 4 shows time–amplitude relation (T–A relation) without correction. Six-order of polynomial is used to do T–A correction. Fig. 5 shows the T–A relation after correction. The time distribution after T–A correction is shown in Fig. 6. The
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W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
Fig. 6. Time spectrum. Time resolution is about 90 ps. Fig. 3. Amplitude spectrum.
Fig. 4. The T–A relation.
distributions are fitted with Gaussians, and we obtain a variance, s; of 120 ps. After subtracting the mean time jitter introduced by two scintillation counters (4PMTs), we obtain 90 ps time resolution. Certainly, the performance of MRPC depends on the gas mixture and different temperatures. Fig. 7 shows efficiency with different working gases. Fig. 8 shows average charge induced in the MRPC with different working gases. With the increase of high voltage, detection efficiency increases. It can be seen that the MRPC chamber reaches its efficiency plateau from a HV 14.5 kV. The maximum efficiency of cosmic ray test system (90%) is lower than the experiment in CERN PST10 [5], this phenomenon is mainly caused by an imperfect geometrical arrangement of the trigger system. Fig. 9 shows time resolution with different working gases. Based on the same reason, the time resolution is worse than in Ref. [5]. Fig. 10 shows noise rate with different working gases. For convenience, we define pure C2H2F4 as gas A, 94.7% C2H2F4+5.3% iso-butane as gas B and 90% C2H2F4+10% iso-butane as gas C. From the four figures, we can obtain the following results.
Fig. 5. The T–A relation after correction.
The high-voltage plateau (time resolution o100 ps) of the module in gas A is shorter than in gases B and C. This is a fatal disadvantage of using the MRPC detector. Efficiency in gas C is much lower than in gases A and B. C2H2F4 is a kind of electronegative
ARTICLE IN PRESS W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
Fig. 7. Efficiency with different working gases.
Fig. 9. Time resolution with different working gases.
Fig. 8. Average charge with different working gases.
Fig. 10. Noise rate with different working gases.
gas, it can prevent the progression of avalanche. The MRPC works in avalanche mode, when the applied voltage is very high (for example the high voltage excesses 14.5 kV), a lot of avalanches will be developed to streamers. So a relatively larger amplitude is obtained. Isobutane can quench the streamer. So adequate ratio of iso-butane mixed with C2H2F4 (gas B) will reduce the output amplitude. In gas C, the output amplitude increases, but the efficiency decreases, this can be seen in Figs. 7 and 8. This phenomenon is very interesting and it is difficult to give a reasonable explanation. We will do further research on this phenomenon.
429
If there is no iso-butane (gas A) or too much isobutane (gas C) in the working gas, the noise of the MRPC module increases greatly. So an adequate fraction of iso-butane can reduce noise. The MRPC module working in gas B has good time resolution and high efficiency. This explains that suitable ratio iso-butane mixed with C2H2F4 is favorable for the performance of the MRPC module.
Figs. 11 and 12 show that noise and dark current change as a function of temperature. The working gas is gas B and the voltage is 14 kV. It
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W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
performance will degrade. On the one hand, time resolution degrades, on the other, the increase of dark current will augment the load of the high voltage source. The most important result is that the MRPC module has to work in temperature lower than 301C.
5. Conclusions According to the results from the cosmic ray test, the performance of the MRPC can be concluded as the following: Fig. 11. Noise in different temperatures.
Fig. 12. Dark current in different temperatures.
can be seen that with the increase in temperature, noise rate and dark current increase. As we know, when the temperature increases, both the pressure of the working gas and the density also increase, as a result, the noise and dark current of the MRPC increase. When the temperature exceeds 301C, noise and dark current increase sharply, so the
The MRPC module can work very well with gas mixture which contains 94.7% C2H2F4+5.3% iso-butane. If there is no iso-butane or the fraction of iso-butane is too large, the performances of the MRPC module degrade. The MRPC module has to work in temperature lower than 30 1C. The MRPC module has good time resolution (o100 ps) and high efficiency (495%). It provides performances comparable to the scintillator-based TOF technology but offering a significantly lower price per channel and its compact mechanics and magnetic compatibility. It can be used as TOF detector for the STAR experiment at RHIC or other experiments.
References [1] B. Bonner, G. Eppley, J. Lamas-Valverde, et al., Nucl. Instr. and Meth. A 478 (2002) 176. [2] A. Akindinov, F. Anselmo, et al., Nucl. Instr. and Meth. A 456 (2000) 16. [3] M. Spegel, Nucl. Instr. and Meth. A 453 (2000) 308. [4] M.C.S. Williams, E. Cerron, et al., Nucl. Instr. and Meth. A 434 (1999) 362. [5] M. Shao, L.J. Ruan, et al., Nucl. Instr. and Meth. A 492 (2002) 344.
Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430 www.elsevier.com/locate/nima
Study on the performance of multi-gap resistive plate chambers Wang Yi, Li Yuanjing, Cheng Jianping, Li Jin, Yue Qian, Lai Yongfang, Tang Le, Fu Jinhua Engineering Physics Department, Tsinghua University, Beijing 100084, China Received 3 December 2003; received in revised form 24 August 2004; accepted 17 September 2004 Available online 27 October 2004
Abstract A kind of multi-gap resistive plate chamber (MRPC) was developed for the STAR experiment at RHIC. The MRPC has excellent time resolution with high efficiency and can be used as the time-of-flight detector. In this paper, we present some performance of MRPC tested by cosmic ray, and performances of MRPC working in different gas mixture and in different temperature are also illustrated. r 2004 Elsevier B.V. All rights reserved. Keywords: MRPC; Cosmic ray; TOF
1. Introduction The multi-gap resistive plate chamber (MRPC) has good time resolution (less than 100 ps) and high detection efficiency (higher than 95%) and is a good candidate for the time-of-flight (TOF) detector for the STAR experiment at RHIC [1,2]. It is low cost and can be segmented according to requirements [3,4]. The MRPC consists of a stack of glass plates, spaced one from the other with spacers of equal thickness creating a series of gas gaps. Electrodes are connected to the outer surfaces of the two outer glass plates. A strong electric field is generated in each subgap by Corresponding
author. Tel.: +86 10 62794480; fax: +86 10 62781133. E-mail address: [email protected] (W. Yi).
applying a high voltage on the external electrodes. All the internal glass plates are left electrically floating, they take the voltage as defined by electrostatics. Typical resistivity for the glass plates is on the order of 1012–1013 O cm. The electrodes are made of resistive graphite tape and are transparent to charge. Copper pickup pads are used to read out the signals.
2. Structure of MRPC module Fig. 1 shows the structure of the MRPC module. The module consists of six pads. The size of each pad is 3.1 6.0 cm2. There is a 3 mm interval between each pad. The total active area of one module is 18.6 6.0 cm2. The glass plate is
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.09.026
ARTICLE IN PRESS 426
W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
Fig. 1. Structure of the MRPC module. (a) Long side view, (b) short side view.
0.52 mm thick and the resistivity is around 8 1012 O cm. There are six gas gaps of about 220 mm defined by nylon fishing-line of this diameter. The electrodes are made of a graphite tape with a surface resistivity of 7.6 105 O/square which covers the entire active area. We use a nonflammable gas mixture which contains 94.7% tetra-fluoro-ethane and 5.3% iso-butane. When a charged particle goes through the chamber the avalanche generates in the gas gaps. The induced signal on the pads is the average of possible avalanches from all gas gaps.
3. Cosmic ray test system Cosmic ray test system is used to measure the performance of MRPCs. Fig. 2 shows the diagram of the test system. The system consists of three
25 cm 5 cm 5 cm plastic scintillation counters with photo-multiplier tubes (PMTs). N415 discriminator (products of CAEN) is used for discrimination of signals from five PMTs. The coincidence signal between PMT1 and PMT5 provides the cosmic trigger for the ADC gate and the stop signal for the TDC converter. The stop time is determined by the leading edge of the pulse from PMT1. PMT1 determines the rate of accidentals and is also used to correct the efficiency accordingly. All signals from PMT2 to PMT5 are fed into a VME TDC (C.A.E.N V775, 35 ps bin width is chosen) as a start signal for digitization. The time resolution for average timing of four PMTs, (t2+t3 t4 t5)/4, is about 80 ps. The MRPC is mounted in a gas tight box flushed with the working gas, and connected to a front end electronics (FEE) card identical to those in use on the TOF (time-of-flight system based on
ARTICLE IN PRESS W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
PMT3
Scintillator 1
PMT1
Scintillator 2
PMT2
427
MRPC1 MRPC2
Scintillator 3
PMT4
PMT5
delay PMT1
Discrim 1
PMT2
Discrim 2
PMT3
Discrim 3
delay
stop
T V D PMT4
Discrim 4
PMT5
Discrim 5
C six channel TDC 6-cell MRPC
E
FEE
gate delay six channel ADC
M
A D C
Fig. 2. The block diagram of the cosmic ray test system.
MRPC technology) system. The analog and digital outputs from the FEE card are connected to the ADC (C.A.E.N V265) and TDC modules. An electrothermal wire is put in the box. The temperature of the MRPC in the box can be controlled by applying adequate voltage on the wire. The VME system connects the PC computer via an optical fiber. Labview6.0 program is used to control the ADC and TDC, read data from the ADC and TDC and display their corresponding spectrum in real time.
4. Results Ten MRPCs have been constructed and are all tested in the same condition (using the same
device, gas mixture and high voltage). Figs. 3–6 show the performance of a typical MRPC with a voltage 14 kV and with the working gas that contains 94.7% C2H2F4 and 5.3% iso-butane. Fig. 3 shows the amplitude spectrum of the MRPC. The charge per channel of V265 ADC is 0.2 pC, and the pedestal is about 250 with a gate width of 100 ns. The signals produced in the MRPC are first amplified by MAXIM3760 amplifier in FEE, and later fed into the ADC. The average charge produced in the MRPC by cosmic ray and recorded by the ADC is around 40 pC. Fig. 4 shows time–amplitude relation (T–A relation) without correction. Six-order of polynomial is used to do T–A correction. Fig. 5 shows the T–A relation after correction. The time distribution after T–A correction is shown in Fig. 6. The
ARTICLE IN PRESS 428
W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
Fig. 6. Time spectrum. Time resolution is about 90 ps. Fig. 3. Amplitude spectrum.
Fig. 4. The T–A relation.
distributions are fitted with Gaussians, and we obtain a variance, s; of 120 ps. After subtracting the mean time jitter introduced by two scintillation counters (4PMTs), we obtain 90 ps time resolution. Certainly, the performance of MRPC depends on the gas mixture and different temperatures. Fig. 7 shows efficiency with different working gases. Fig. 8 shows average charge induced in the MRPC with different working gases. With the increase of high voltage, detection efficiency increases. It can be seen that the MRPC chamber reaches its efficiency plateau from a HV 14.5 kV. The maximum efficiency of cosmic ray test system (90%) is lower than the experiment in CERN PST10 [5], this phenomenon is mainly caused by an imperfect geometrical arrangement of the trigger system. Fig. 9 shows time resolution with different working gases. Based on the same reason, the time resolution is worse than in Ref. [5]. Fig. 10 shows noise rate with different working gases. For convenience, we define pure C2H2F4 as gas A, 94.7% C2H2F4+5.3% iso-butane as gas B and 90% C2H2F4+10% iso-butane as gas C. From the four figures, we can obtain the following results.
Fig. 5. The T–A relation after correction.
The high-voltage plateau (time resolution o100 ps) of the module in gas A is shorter than in gases B and C. This is a fatal disadvantage of using the MRPC detector. Efficiency in gas C is much lower than in gases A and B. C2H2F4 is a kind of electronegative
ARTICLE IN PRESS W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
Fig. 7. Efficiency with different working gases.
Fig. 9. Time resolution with different working gases.
Fig. 8. Average charge with different working gases.
Fig. 10. Noise rate with different working gases.
gas, it can prevent the progression of avalanche. The MRPC works in avalanche mode, when the applied voltage is very high (for example the high voltage excesses 14.5 kV), a lot of avalanches will be developed to streamers. So a relatively larger amplitude is obtained. Isobutane can quench the streamer. So adequate ratio of iso-butane mixed with C2H2F4 (gas B) will reduce the output amplitude. In gas C, the output amplitude increases, but the efficiency decreases, this can be seen in Figs. 7 and 8. This phenomenon is very interesting and it is difficult to give a reasonable explanation. We will do further research on this phenomenon.
429
If there is no iso-butane (gas A) or too much isobutane (gas C) in the working gas, the noise of the MRPC module increases greatly. So an adequate fraction of iso-butane can reduce noise. The MRPC module working in gas B has good time resolution and high efficiency. This explains that suitable ratio iso-butane mixed with C2H2F4 is favorable for the performance of the MRPC module.
Figs. 11 and 12 show that noise and dark current change as a function of temperature. The working gas is gas B and the voltage is 14 kV. It
ARTICLE IN PRESS 430
W. Yi et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 425–430
performance will degrade. On the one hand, time resolution degrades, on the other, the increase of dark current will augment the load of the high voltage source. The most important result is that the MRPC module has to work in temperature lower than 301C.
5. Conclusions According to the results from the cosmic ray test, the performance of the MRPC can be concluded as the following: Fig. 11. Noise in different temperatures.
Fig. 12. Dark current in different temperatures.
can be seen that with the increase in temperature, noise rate and dark current increase. As we know, when the temperature increases, both the pressure of the working gas and the density also increase, as a result, the noise and dark current of the MRPC increase. When the temperature exceeds 301C, noise and dark current increase sharply, so the
The MRPC module can work very well with gas mixture which contains 94.7% C2H2F4+5.3% iso-butane. If there is no iso-butane or the fraction of iso-butane is too large, the performances of the MRPC module degrade. The MRPC module has to work in temperature lower than 30 1C. The MRPC module has good time resolution (o100 ps) and high efficiency (495%). It provides performances comparable to the scintillator-based TOF technology but offering a significantly lower price per channel and its compact mechanics and magnetic compatibility. It can be used as TOF detector for the STAR experiment at RHIC or other experiments.
References [1] B. Bonner, G. Eppley, J. Lamas-Valverde, et al., Nucl. Instr. and Meth. A 478 (2002) 176. [2] A. Akindinov, F. Anselmo, et al., Nucl. Instr. and Meth. A 456 (2000) 16. [3] M. Spegel, Nucl. Instr. and Meth. A 453 (2000) 308. [4] M.C.S. Williams, E. Cerron, et al., Nucl. Instr. and Meth. A 434 (1999) 362. [5] M. Shao, L.J. Ruan, et al., Nucl. Instr. and Meth. A 492 (2002) 344.