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RPC working gas (C 2 H 2 F 4 /i-C 4 H 10 /SF 6 ): Simulation and measurement. Jingbo Wang Department of Engineering Physics, Tsinghua University, Beijing, China. 10th RD51 Collaboration Meeting , Oct 4th, 2012, Stony Brook. Outline. Multi-gap Resistive Plate Chamber (MRPC)
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RPC working gas (C2H2F4/i-C4H10/SF6): Simulation and measurement Jingbo Wang Department of Engineering Physics, Tsinghua University, Beijing, China 10th RD51 Collaboration Meeting, Oct 4th, 2012, Stony Brook
Outline • 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) differential pre-amplifier particle standard PCB with read-out strips on one side HV distribution by a medium resistivity layer (e.g. Graphite) transparent to the induced signals Rin HV insulator +HV gas gaps (~0.22 mm) -HV HV coating with R~2 MΩ/□ Resistive electrodes (glass. bakelite) Time resolution: 20 - 100 ps Efficiency: >90% * The multi-gap structure: E. Cerron Zeballos, et al., Nucl. Instr. and Meth. A 374 (1996) 132.
MRPCs @ Tsinghua STAR-TOF STAR-MTD 4032 modules for STAR-TOF 120 modules for STAR-MTD CBM-TOF Y. Wang, J. Wang, et al., Nucl. Instr. and Meth A 613 (2010) 200–206 Y. Wang, et al., Nucl. Instr. and Meth A 640 (2011) 85–90 J. Wang, et al., Nucl. Instr. and Meth. A 621 (2010) 151. Rate capability: >20 kHz/cm2
MRPCs @ Tsinghua Low-resistivity doped glass 50cm * 50cm ~1010Ωcm MRPC Workshop modules for STAR-TOF modules for STAR-MTD Modules for CBM-TOF: rate capability up to 70kHz/cm2
l E x Ions Electrons Motivation of the simulation • 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 First step: the latest electron swarm parameters Region: A, B, C, D, E 1.5-D model (Lippmann): a factor of 2 discrepency in the charge spectrum • intrinsic time resolution: sT ~ 50 ps • rate capability: R ~ 0.5 – 25 kHz/cm2 W. Riegler, et al., Nucl. Instr. and Meth A 500 (2003) 144–162 C. Lippmann, et al., Nucl. Instr. and Meth. A 517 (2004) 54–76
Experimental measurement: C2H2F4 The initial electrons were released by a UV flash. Pulse Townsend technique! Current fit The displacement current was fitted by the expression: Te 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 41 J.L. Hern´andez-´Avila, E. Basurto, J. de Urquijo, J. Phys. D 35, 2264 (2002), and references therein J. de Urquijo
Experimental measurement: i-C4H10 • I.B. Lima Chamber Current fit P. Fonte, et al., Nucl. Instr. and Meth. A 613 (2010) 40–45 I.B. Lima, et al., Nucl. Instr. and Meth. A 670 (2012) 55–60 P. Fonte
Experimental measurements: Mixtures • G. Chiodini, • C2H2F4/i-C4H10/SF6 = 94.7/5/0.3 The alpha in figure is performed with the empirical formula α*/P VS p/E • A. Colucci, C2H2F4/i-C4H10 = 97/3, 90/10 A. Colucci, et al., Nucl. Instr. and Meth. A 425 (1999) 84-91 G. Chiodini, et al., Nucl. Instr. and Meth. A 602 (2009) 757-760
Simulations of the electron swarm parameters    R. Veenhof, Garfield - simulation of gaseous detectors, http://garfieldpp.web.cern.ch/garfieldpp/  S.F. Biagi, Nucl. Instr. and Meth. A 421 (1999) 234Ð240 • Garfield++ • C2H2F4 • Iso-butane • SF6 • Mixtures • Magboltz 8.9.2 • Different solutions in Magboltz • Comparison between simulations and measurements • Cross-sections
Garfield++: C2H2F4, Ve C2H2F4 / Ar mixture 100/0 50/50 20/80 10/90 Nice agreement! Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)
Garfield++: C2H2F4, Alpha* C2H2F4 / Ar mixture 100/0 50/50 20/80 10/90 Nice agreement! Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)
Garfield++: C2H2F4, Dl C2H2F4 / Ar mixture 100/0 50/50 10/90 20/80 Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)
Garfield++: i-C4H10, Alpha and Ve VS Magboltz 2.8.6 (very old version) Garfield++ (latest version)  P. Fonte  I.B. Lima RPC working point: 400 Td  P. Fonte, et, al., Nucl. Instr. and Meth. A 613 (2010) 40–45  I.B. Lima et, al., Nucl. Instr. and Meth. A670 (2012) 55–60 Nothing has changed with i-C4H10
Garfield++: SF6,Alpha*, Ve Ve Alpha* L. G. Christophorou, et, al., J. Phys. Chem. Ref. Data, Vol 29, No. 3, 2000
Garfield++: Mixtures, Alpha* and Ve Magboltz 7.0 Garfield++ / Magboltz 8.9.7 P. Fonte, not published Disagreement for RPC gas mixtures (C2H2F4, i-C4H10, SF6) D. Gonzalez-Diaz, et, al., Nucl. Instr. and Meth. A 661 (2012) S172–S176
Different solutions in Magboltz 8.9.2 Experimental definitions 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 of both position and time. Garfield++ takes the SST solution for alpha (MC solution if no SST output), and the MC solution for the others. • 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 Y Sakai, et, al., J. Phys. D: Phy., Vol. 10, 1977
Magboltz 8.9.2: Alpha* C2H2F4 / Ar mixture SST solution MC solution Alpha*/N Space charge correction? Question: which solution is recommended? Data: J de Urquijo, et, al., Eur. Phys. J. D 51, 241–246 (2009)
Magboltz 8.9.2: Ve C2H2F4 / Ar mixture MC solution SST solution Ve
Magboltz 8.9.2: Dl C2H2F4 / Ar mixture SST solution MC solution NDL
Cross-sections C2H2F4 dissociation
Summary Thanks for your attention • Garfield++ and Magboltz: • C2H2F4: Fine • i-C4H10: ? • SF6: Tiny discrepancy • Mixtures: ? • Different solutions in Magboltz • Measurements for RPC gas mixtures are needed.