RPC working gas (C2H2F4/i-C4H10/SF6): Simulation and

measurement

Jingbo WangDepartment of Engineering Physics, Tsinghua University, Beijing, China

10th RD51 Collaboration Meeting, Oct 4th, 2012, Stony Brook

Outline

2

Multi-gap Resistive Plate Chamber (MRPC) Motivation of the simulation Experimental measurements• C2H2F4, J de Urquijo

• i-C4H10, I.B. Lima, P. Fonte

• SF6, L. G. Christophorou

• Mixtures, G. Chiodini, A. Colucci

Simulations of the swarm parameters• Garfield++• Magboltz 8.9.2

Summary

Multi-gap Resistive Plate Chamber (MRPC)

3

Rin

standard PCBwith read-outstrips on oneside

HV insulator

HV coating withR~2 MΩ/□

+HV

-HV

differential pre-amplifier

gas gaps (~0.22 mm)

Resistive electrodes(glass. bakelite)

particle

HV distributionby a medium resistivity layer(e.g. Graphite)transparent to the induced signals

* The multi-gap structure: E. Cerron Zeballos, et al., Nucl. Instr. and Meth. A 374 (1996) 132.

Time resolution: 20 - 100 psEfficiency: >90%

MRPCs @ Tsinghua

4

STAR-MTD

STAR-TOF

CBM-TOF

Rate capability: >20 kHz/cm2

Y. Wang, J. Wang, et al., Nucl. Instr. and Meth A 613 (2010) 200–206Y. Wang, et al., Nucl. Instr. and Meth A 640 (2011) 85–90J. Wang, et al., Nucl. Instr. and Meth. A 621 (2010) 151.

4032 modules for STAR-TOF 120 modules

for STAR-MTD

MRPCs @ Tsinghua

5

50cm * 50cm~1010 Ωcm

modules for STAR-TOF

modules for STAR-MTD

Modules for CBM-TOF: rate capability up to 70kHz/cm2

MRPC Workshop

Low-resistivity doped glass

Motivation of the simulation

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1.5-D model (Lippmann): a factor of 2 discrepency in the charge spectrum

W. Riegler, et al., Nucl. Instr. and Meth A 500 (2003) 144–162C. Lippmann, et al., Nucl. Instr. and Meth. A 517 (2004) 54–76

lE x Ions

Electrons

tVeentn 0)(

n(t) increases exponentially α*Ve dominates the time resolution. Timing RPC is working in avalanche

mode, under space charge regime RPC wroking gas: C2H2F4/i-C4H10/SF6

intrinsic time resolution: T ~ 50 ps

rate capability: R ~ 0.5 – 25 kHz/cm2

Region: A, B, C, D, E First step: the latest electron swarm parameters

Experimental measurement: C2H2F4

• J. de Urquijo

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J. de Urquijo, et al., Eur. Phys. J. D 51, 241–246 (2009)J. de Urquijo, et al., 1999 J. Phys. D: Appl. Phys. 32 41J.L. Hern´andez-´Avila, E. Basurto, J. de Urquijo, J. Phys. D 35, 2264 (2002), and references therein

Current fit

Te

Pulse Townsend technique!

The initial electrons were released by a UV flash.

The displacement current was fitted by the expression:

Experimental measurement: i-C4H10

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• P. Fonte

P. Fonte, et al., Nucl. Instr. and Meth. A 613 (2010) 40–45I.B. Lima, et al., Nucl. Instr. and Meth. A 670 (2012) 55–60

• I.B. Lima

Current fitChamber

Experimental measurements: Mixtures

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• A. Colucci,

C2H2F4/i-C4H10 = 97/3, 90/10

A. Colucci, et al., Nucl. Instr. and Meth. A 425 (1999) 84-91

• G. Chiodini,

C2H2F4/i-C4H10/SF6 = 94.7/5/0.3

G. Chiodini, et al., Nucl. Instr. and Meth. A 602 (2009) 757-760

d

q

q

eqq

eq

P

*0

1

E

B

Aep

*

The alpha in figure is performed with the empirical formula

α*/P VS p/E

Simulations of the electron swarm parameters

• Garfield++ C2H2F4

Iso-butane SF6

Mixtures

• Magboltz 8.9.2 Different solutions in Magboltz Comparison between simulations and measurements Cross-sections

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[1] R. Veenhof, Garfield - simulation of gaseous detectors, http://garfieldpp.web.cern.ch/garfieldpp/[2] S.F. Biagi, Nucl. Instr. and Meth. A 421 (1999) 234Ð240

[1]

[2]

Garfield++: C2H2F4, Ve

11Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)

C2H2F4 / Ar mixture

100/0 50/50

20/80 10/90

Nice agreement!

Garfield++: C2H2F4, Alpha*

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100/0 50/50

20/80 10/90

C2H2F4 / Ar mixture

Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)

Nice agreement!

Garfield++: C2H2F4, Dl

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100/0 50/50

20/80 10/90

C2H2F4 / Ar mixture

Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)

Garfield++: i-C4H10, Alpha and Ve

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Magboltz 2.8.6 (very old version) Garfield++ (latest version)

[1] P. Fonte, et, al., Nucl. Instr. and Meth. A 613 (2010) 40–45[2] I.B. Lima et, al., Nucl. Instr. and Meth. A670 (2012) 55–60

[1] P. Fonte

[2] I.B. Lima

Nothing has changed with i-C4H10

VS

RPC working point: 400 Td

Garfield++: SF6,Alpha*, Ve

15L. G. Christophorou, et, al., J. Phys. Chem. Ref. Data, Vol 29, No. 3, 2000

Alpha* Ve

Garfield++: Mixtures, Alpha* and Ve

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Magboltz 7.0 Garfield++ / Magboltz 8.9.7

D. Gonzalez-Diaz, et, al., Nucl. Instr. and Meth. A 661 (2012) S172–S176

Disagreement for RPC gas mixtures (C2H2F4, i-C4H10, SF6)

P. Fonte, not published

Different solutions in Magboltz 8.9.2

• SST: Steady-state Townsend Solution Drift velocity: Ve Transvers diffusion: Dt Longitudinal diffusion: Dl Townsend coefficient: Alpha Attachment coefficient: Att

• PT: Pulsed Townsend Solution Ionization rate: Ri Attachment rate: Ra

• TOF: Time-of-flight Solution Drift velocity: Wr, Ws Transvers diffusion: Dt Longitudinal diffusion: Dl Effective Townsend coefficient: Alpha-Att

• MC: Monte Carlo (theoretical) solution: Ve, Dt, Dl, Alpha, Att

17Y Sakai, et, al., J. Phys. D: Phy., Vol. 10, 1977

A constant number of electrons is emitted at the cathode, which generates a steady stream of electrons in the uniform electric field between parallel plates.

A group of electrons is released at the cathode and its growth observed by measuring the external current a function of time.

The growth is observed as a function ofboth position and time.

Garfield++ takes the SST solution for alpha (MC solution if no SST output), and the MC solution for the others.

Experimental definitions

Magboltz 8.9.2: Alpha*

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Alpha*/NMC solution SST solution

Space charge correction?

Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)

C2H2F4 / Ar mixture

Question: which solution is recommended?

Magboltz 8.9.2: Ve

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Ve

MC solution SST solution

C2H2F4 / Ar mixture

Magboltz 8.9.2: Dl

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NDL

MC solution SST solution

C2H2F4 / Ar mixture

Cross-sections

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dissociation

C2H2F4

Summary

• Garfield++ and Magboltz: C2H2F4: Fine

i-C4H10: ?

SF6: Tiny discrepancy

Mixtures: ? Different solutions in Magboltz

• Measurements for RPC gas mixtures are needed.

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Thanks for your attention