1. Diego González-Díaz (GSI-Darmstadt) A. Berezutskiy (SPSPU-Saint Petersburg), G. Kornakov (USC-Santiago de Compostela), M. Ciobanu (GSI-Darmstadt), Y. Wang (Tsinghua U.-Beijing), J. Wang (Tsinghua U.-Beijing) Darmstadt, November 24 th, 2009 one year ago

2. Diego González-Díaz (GSI, TU Darmstadt, Tsinghua University) Y. Wang (Tsinghua U.-Beijing), J. Wang (Tsinghua U.-Beijing), C. Huangshan (Tsinghua U.-Beijing), P. Kowina (GSI), P. Moritz(GSI) and the NeuLand-R3B group Darmstadt, February 10 th, 2011 now

3. what has happened since?

4. X workshop on Resistive Plate Chambers and related detectors Darmstadt, February 9-12, 2010. Sponsored by HIC4FAIR.

5. 1.RPC HADES-TOF wall cosmic ray test performance, A. Blanco. 2.FOPI MMRPC ToF barrel. M. Kis. 3.A multipurpose Trigger Readout board. M. Palka. 4.The Slow Control System of the HADES RPC wall. A. Gil. 5.High Resolution TDC ASIC for CBM-TOF, H. Flemming. contributions directly connected to GSI

6. 1.Progress of R&D and production of timing RPCs in Tsinghua University, Yi Wang. 2.A prototype of high rate MRPC for CBM-TOF, J. Wang. 3.Ceramics high rate MRPC for CBM-TOF, L. Naumann 4.Towards a high granularity, high counting rate, differential read-out RPC. M. Petris. 5.The CBM Time-of-Flight wall. I. Deppner. 6.Progress in the simulation of Resistive Plate Chambers with multi-strip readout. D.Gonzalez-Diaz. 7.NeuLand: MRPC-based time-of-flight detector for 1 GeV neutrons. D. Bemmerer. 8.Development of MMRPC prototypes for R3B, FAIR. U. Datta Pramanik. 9.Some results of the R&D of a ToF-wall to identify relativistic ions. E. Casarejos. 10.Design and construction of iToF: a ToF-wall detector to identify relativistic ions in R3B, FAIR, E. Casarejos. 11.A closed-circuit gas-recirculation system for RPC detectors. D. Rossi. 12.NeuLand MRPC-based detector prototypes tested with fast neutrons. C. Caesar. 13.Testing timing RPCs at ELBE/Dresden using 32MeV single-electron bunches with picosecond time resolution. D. Stach. 14.NeuLAND MRPC prototypes tested at ELBE/Dresden. D. Yakorev. contributions directly connected to FAIR

7. ->28% of the workshop contributions were connected to GSI/FAIR. ->70% of the workshop contributions related to time-of-flight ((and)multigap, (and)multistrip) RPCS were connected to GSI/FAIR.

8. R 3 B/itof (SIS100) GSI-FAIR in a nutshell (as of today) R 3 B/neuLand (SIS100) CBM (SIS100/SIS300) FOPI (SIS18) FOPI (SIS18/SIS100)

9. progress on the simulation and understanding of the counters

10. The simulation scheme in a nutshell generation + induction 1 transmission 2 FEE response 3 multi-strip 4

11. 1.Dedicated measurements of transmission properties and benchmark of the electrostatic solver and modeling: -Before: APLAC simulations(FDTD). -Now: MAXWELL-2D(FEM) + analytical solutions of lossy telegrapher's equations. 2. Calculation of the induction profiles: -Before: analytical calculation (approximate). -Now: MAXWELL-2D(FEM). Analytical calculation used only for benchmarking the code. 3.Change of philosophy: -Before: work with induced charges (~slow amplifier). -Now: work with induced currents (broad-band amplifiers). 4. More realistic implementation of the Front End Electronics. 5.New parameters of the gas. MAGBOLTZ cross-sections re-obtained to be consistent with 2009data for C 2 H 2 F 4. 6. A simple parameterization of streamer formation introduced, based on data. 7. Started porting the code MATLAB-based to C++ for usage in FAIRroot both for R3B and CBM (~50% done). What is new?

12. 1. Upgrades in signal transmission transmission 2

13. Experimental verification of electrostatic compensation 2m!

14. Transmission characteristics in time-domain (I)

15. Transmission characteristics in time-domain (II)

16. figures of merit for typical signals

17. transmission characteristics in frequency-domain transmission near-end cross-talk far-end cross-talk transmission (single-strip)

18. possibly the most important figure of merit the cross-talk to the over-next neighbor is the relevant figure of merit!

19. The CBM-TOF wall. Design requirements compensation for N-strips requires of the following conditions: Diego Gonzalez-Diaz, Chen Huangshan, Yi Wang, arXiv.1102.1389 generally satisfied generally not satisfied  then all the system velocities become equal! (no modal dispersion) details and proof in:

20. induction 1 2. Upgrades on signal induction and charge profiles

21. 'Weighting field' technique for calculating induction profiles analytic calculation MAXWELL-2D calculation The analytical calculation usually fails in between strips

22. induction 1 3. Upgrades on avalanche modeling this part is still considerably behind the 'state of the art' simulations (the practical importance of a better modelization is not clear)

23. Determination of C 2 H 2 F 4 cross-sections from most recent data. MAGBOLTZ accuracy improved down to 1%. (S. Biagi) before now

24. Avalanche model constrained by world-wide survey efficiencycharge distribution + streamer parameterized in a crude way (when avalanche reaches a certain charge it 'explodes' into a streamer) Diego Gonzalez-Diaz, doi:10.1016/j.nima.2010.09.067

25. FEE response 3 3. Upgrades on FEE modeling

26. Upgrades on FEE modeling (based on APLAC) Modeling this is the weakest part so far. Requires hands-on work. Can not be modeled without detailed measurements. The main parameters of the electronics (threshold, gain) are now fixed to describe data simplified sketch of the FEE developed by the RICE University (STAR)

27. how does it look like?

28. ~center of strip ~region between strips representation gain=1 V th equivalent at input modestly fast ~100evts/s

29. some results

30. multi-strip prototypes for CBM

31. two selected chambers 24cm-long, 5x2(0.25gap) 1m-long, 6x2(0.22gap)

32. charge distributions Triggered events 24cm-long, 5x2(0.25gap)

33. Triggered events charge distributions 1m-long, 6x2(0.22gap)

34. Triggered events and RPC fired charge distributions 1m-long, 6x2(0.22gap)

35. efficiency and cross-talk resolution Global response

36. efficiency profiles

37. efficiency profiles (with ideal position information)

38. multi-strip prototypes for R3B. Transmission. D. Yakorev et al. submited to NIM A

39. Global response. Electrons at ELBE (~mips).

40. Outlook ● A MATLAB toolbox for fast RPC characterization is close to be finished. A fast scheme to simulate these counters has been implemented. ● With a larger scope, a software package is being created and integrated in FAIRroot. Results have not been presented here (see my talks at the last CBM collaboration meeting). The amount of work done, as compared to the MATLAB toolbox is ~50%. Speed is comparable, at present. ● Measurements on transmission and FEE characterization have to be done at least once, anyhow. Simulations are too much detail-sensitive. Simulations of this type will hardly replace measurements.

41. Appendix

42. -V +V 1m the inocent problem

43. -V +V 1m I) a signal is induced due to the movement of the avalanche charges. The influenced area is very localized. II) the signal must travel till the end of the structure III) the signal must be measured at the end of the structure CgCg CmCm LoLo LmLm R R ?

44. -V +V 1m the signal starts moving due to the mutual inductance a current of magnetic origin with opposite sign couples to the neighbor strip (Lenz law) CgCg CmCm LoLo LmLm R R a signal is electrically coupled through the mutual capacitance, with equal strength for both ends

45. -V +V 1m CgCg CmCm LoLo LmLm R R x after a series of 'minor' reasonable assumptions... (~usually termed 'low coupling') summing up the contributions of infinite C/L elements along the line

46. increases with the unbalance between capacitive and inductive coupling. It can change sign! increases with the propagation distance increases with the signal slope/rise-time can we make this zero? A rigorous derivation of the expression for I ct starting from the telegrapher's equations provides the same result in the low-coupling limit

47. problem: inductances are not very intuitive for most of people solution: a well known theorem relates the inductance with the capacitance matrixes of the structure in empty space (more intuitive, although not directly measurable) when is this zero?. When the field lines couple through a single dielectric material. When it is zero we will say that the system is 'electrostatic compensated'.

48. the basic questions: is it possible to reasonably compensate an inhomogeneous structure? even if we manage, can we compensate if we have more than 2 strips? (for most RPCs, yes) (for some RPCs, yes) even if we manage, what happens if the system is lossy (R,G) ? (quite ok, but be careful) R G G

49. A multi-gap RPC in general. Here a differential RPC ('a la' STAR), just for the sake of 'electrical elegance' R in standard PCB with read-out strips on one side HV insulator with V break >10-15 kV HV coating with R~100 MΩ/□ +V -V differential pre-amplifier at least 4 gas gaps (~0.3 mm thick) float glass particle *parameters not from STAR

50. More electrical schemes are (un)fortunately possible ALICE-LHC V -V STAR-RHIC V -V V HADES-SIS -V FOPI-SIS -V V all these schemes are equivalent regarding the underlying avalanche dynamics... but the RPC is also a strip- line, and this is manifested after the avalanche current has been induced. And all these strip-lines have a completely different electrical behavior. -V V V V S. An et al., NIM A 594(2008)39 [10] ! HV filtering scheme is omitted

51. Avalanche generation. A simple avalanche model The stochastic solution of the avalanche equation is given by a simple Furry law (non- equilibrium effects are not included). Avalanche evolution under strong space- charge regime is characterized by no effective multiplication. The growth stops when the avalanche reaches a certain number of carriers called here n e,sat. The amplifier is assumed to be slow enough to be sensitive to the signal charge and not to its amplitude. We work, for convenience, with a threshold in charge units Q th. log 10 n electrons ~7 toto t space-charge regime exponential-growth regime ~7.5 t meas avalanche Furry-type fluctuations ~2 Raether limit 8.7 exponential-fluctuation regime threshold 0 simplifying assumptions

52. Induction and weighting field E z t=2.5 mm w=22 mm HV read-out wide-pad limit t << w additionally when g<<t (typical situation) E z does not depend on the position –z- along the gap g=0.3 mm w s-s ~0 mm T. Heubrandtner et al. NIM A 489(2002)439 We adapted to multi-gap the formulas from: problem: under-estimation of E z for large inter-strip separations

53. Cross-talk in a 2-strip RPC modeled as a loss-less transmission-line (I) two different modes in the transmission line!. This causes 'modal dispersion' unless: true for homogeneous transmission lines! a 4-gap RPC seen as a transmission-line dominated by skin-effect: small for typical dimensions and rise-times very small, due to the presence of gas and glass for typical materials (glass) loss-less line! W. Riegler, D. Burgarth, NIMA 481(2002)130 [12] see if 1) 2)

54. for exponential signals low-frequency /small distance / non-dispersive limit high-frequency /large distance / dispersive limit small dispersion very large dispersion z o = position along the strip where the signal is induced see also [12] the 2 modes are fully decoupled Cross-talk in a 2-strip RPC modeled as a loss-less transmission-line (II). Limits.

55. History revisited: 1.6m-long 2-strip RPC (P. Fonte et al., 2002) width = 5cm strip separation = 1mm glass = 3mm gap = 0.3mm length= 1.6m

56. Cross-talk in Fonte multi-strip RPC

57. C g =521 pF/m C m =88 pF/m F ct =50% ! BW=1.5 GHz R in =50 Ω very dispersive! experimental conditions: Π, E=3.5 GeV, low rates, trigger width = 2 cm F ct =40% 'fine-tunning' 80%-90% measured cross-talk levels reproduced Z c ~13 Ω transverse scan Cross-talk in Fonte multi-strip RPC HV=5.7 kV

58. x10 ->increase strip separation CgCg CmCm Δv/v t rise Minimizing cross-talk (I)

59. x6 /2.5 /6 ->increase strip/width separation ->reduce glass thickness CgCg CmCm Δv/v t rise Minimizing cross-talk (II)

60. x6 /2.5 /6 BW/10 ->increase strip/width separation ->reduce glass thickness ->reduce band-width CgCg CmCm Δv/v t rise low coupling low dispersion Minimizing cross-talk (III)

61. guard strip ->put guard strip CgCg CmCm Δv/v t rise Minimizing cross-talk (IV)

62. not mirrored ->use only two electrodes CgCg CmCm Δv/v t rise (it flips!) Minimizing cross-talk (V)

63. not mirrored coupling to PCB ->use only two electrodes ->couple locally to ground CgCg CmCm Δv/v t rise low coupling NO dispersion Minimizing cross-talk (VI)

64. Minimizing cross-talk + detector response (I)

65. x10 Minimizing cross-talk + detector response (II)

66. x6 /2.5 /6 Minimizing cross-talk + detector response (III)

67. x6 /2.5 /6 BW/10 Minimizing cross-talk + detector response (IV)

68. not mirrored coupling to PCB Minimizing cross-talk + detector response (V)

69. Ideal case: no cross-talk + perfect tracking

70. 'some' of the new CBM prototypes (preliminary short compilation)

71. 35-cm long wide-strip, mirrored and shielded... Z c ~18 Ω BW=260 MHz R in =100 Ω F ct =11%little dispersive experimental conditions: ~mips from p-Pb reactions at 3.1 GeV, low rates, trigger width = 2 cm F ct =19% 'fine-tunning' inter-strip region dominated by trigger width probability of pure cross-talk: 1-3% Analysis with high resolution tracking on-going. transverse scan CgCg CmCm

72. 1-m long counter, 6-strip RPC, 12-gap, mirrored and shielded... experimental conditions: ~mips from p-Pb reactions at 3.1 GeV, low rates, trigger width = 2 cm (< strip width) long run. Very high statistics. No simulations available yet

73. no double hit double-hit in any of 1 st neighbors double-hit in any of 2 nd neighbors double-hit in any of 3rd neighbors 1-m long counter, 12-gap, mirrored and shielded No simulations available yet

74. 1-m long counter, 12-gap, mirrored and shielded

75. conclusions and outlook Multi-strip design of timing RPCs at 1-m scale with acceptable cross-talk, small cluster size and small deterioration of time resolution seems doable. Further optimized structures based on simulations are on the way (F ct ~1%). For making a multi-strip fully robust against streamer-crosstalk there is still a long way to go (maybe impossible). -> Detailed optimization based on physics performance soon to follow. Then we will know if cross-talk is 'high' or not.

76. Multi-strip-MRPC (MMRPC) 1.1 mm Glass: ε=7.5, strip width = 1.64 mm, strip gap = 0.9 mm, strip length = 900 mm 1.1 mm 0.5 mm 0.22 mm copper (20 μm) 8 gaps The FOPI counter

77. Induction. Example FOPI case.

78. cathode 1 50 anode 1 50 cathode 2 50 anode 2 50 cathode 3 50 anode 3 50 cathode 4 anode 4 50 cathode 5 50 anode 5 50 Cross-talk in an un-terminated line signal from BC420 scintillator (used as current generator)

79. cathode 1 50 anode 1 50 cathode 2 50 anode 2 50 cathode 3 50 anode 3 50 cathode 4 50 anode 4 50 cathode 5 50 anode 5 50 Cross-talk in a terminated line

80. Cross-talk and signal shape cross-talk constant, very independent from the signal shape low dispersion counter, typical working conditions, BW=260 MHz Take as a typical shape the one of an avalanche produced at the cathode Even for dispersive counters it is reasonable since most of the charge is coming from that region

81. The FOPI counter (11 th strip) 50 anode 0 50 anode 1 50.......... 50 anode 11 50 anode 12 50 cathode 50 anode 13 50 anode 14 50 anode 15

82. The FOPI counter (9 th strip) 50 anode 0 50 anode 1 50.......... 50 anode 9 50 anode 10 50 cathode 50 anode 11 50 anode 12 50.......... 50

83. 50-cm long, mirrored and not shielded...

84. ~1-m long, non-mirrored and shielded...

85. several electrons (I) An ionizing particle at fixed energy creates an average number of ionizations n o randomly distributed along the gap, with each cluster having a (1/n e in cluster ) 2 probability to produce more than 1 electron. This is very easy to generate. Then each cluster can be made to fluctuate according to Furry law. HEED calculation

86. A parentheses: rate capability of various CBM prototypes for small fluxes and in a simple DC-model see for instance: D. Gonzalez-Diaz et al. Nucl. Phys. B (Proc. Suppl.) 158(2006)111

87. A parentheses: rate capability and DC-model systematics In first order, it fits!

88. prompt (e-) component Slow (ion) component g/v e ~ 1 nsg/v i ~1 μs E=ΔV/g particle e - -I + How (we believe) is the avalanche produced? i th space-charge limitation E av ~E avalanche growth decreases! τ g ~ 1 s (glass relaxation time) see [4], for instance

89. First of all... what is a strip? In this talk: A strip is a read-out structure that must be described (due to the phenomena under study) like a transmission-line. In the simplest single-strip description, it is something characterized by 2 magnitudes: a transmission coefficient and a propagation velocity. This is a definition based on the electrical properties of the structure. In standard language: - strip: something read-out in two ends/something 'quite rectangular' - pad: something read-out in one end/something 'quite squared'

90. Induction + transmission + FEE. Sketch (II) Five stages in order to get a predictive result Avalanche generation with the previous code. [->Comparison with eff vs V and fine-tune, if needed, of threshold value. This approach seems to be flexible enough.] Induction, based on analytical formulas from [13], extrapolated to multiple-gaps by using the effective series permittivity of the corresponding group of layers. Propagation based on HF simulator APLAC (http://web.awrcorp.com/Usa/Products/APLAC/).http://web.awrcorp.com/Usa/Products/APLAC/ [-> Validation of APLAC for the structure of interest with a pulse generator (nowadays we do not need this step anymore)] Termination and other circuit elements are included, together with FEE, simulated also with APLAC.

91. A 2-strip RPC as a loss-less transmission-line. Example (III) 2-strip geometry and signal taken from [12] injected signalcross-talk signal non-dispersive limit (z o =0) dispersive limit (z o ->∞) ->Continuous line is the exact analytical solution from [12]. ->Dashed and dotted lines are the numerical solution from APLAC used later in this work.

92. Measurements of cross-talk with RPC mockup

93. Typical plots where to look at Transverse profile of the efficiency, with and w/o valid charge. Cross-talk probability. Integral and as a function of the charge in the main strip. Resolution when a second hit is present in the module. Cluster sizes (not shown here). Dependence with HV of the above observables (not shown here).

94. 50-cm long wide-strip, mirrored and not shielded... probability of pure cross-talk: 1-3% similar cross-talk levels than in previous case experimental conditions: ~mips from p-Pb reactions at 3.1 GeV, low rates, trigger width = 2 cm (< strip width) BW=260 MHz R in =100 Ω Z det ~20 Ω C m =18 pF/m C g =276 pF/m dispersive C m /C g =6.5% F ct =11.5%

95. 30-cm long narrow strip, differential... C m =20 pF/m C diff =23 pF/m F ct =9% experimental conditions: ~mips from p-Pb reactions at 3.1 GeV, low rates, high resolution (~0.1 mm) tracking probability of pure cross-talk: 1-3% intrinsic strip profile is accessible! Z diff =80 Ω dispersive transverse scan