Presented by: Katayoun Doroud World Laboratory fellow under Supervision of: Crispin Williams ALICE TOF General meeting, CERN – Build 29, 9 December 2009

MRPC Simulation Procedure considering space charge effects. Simulation results for ALICE TOF 10 gap MRPC Conclusion & outlook ALICE TOF General meeting, CERN – Build 29, 9 December 2009

Simulation of a single gap RPC. “n” events randomly chosen and summed up together. This will provide a single event for the MRPC. Event 1 Event 2Event n ALICE TOF General meeting, CERN – Build 29, 9 December 2009

1- The gap has been divided into small steps (500) E0E0 2- The through-going charged particles passes perpendicularly through the gas gap 3- HEED++ program used to simulate the creation of the primary ionization (electrons and positive ions) 4- Each primary electron-ion pair has then been placed at the correct position inside the gas gap 5- The actual electric field strength calculated dynamically at each step (actual electric field = applied electric field + electric field of space charge) ALICE TOF General meeting, CERN – Build 29, 9 December 2009

6- Recalculation of avalanche parameters (v, α, η), the new value of the avalanche parameters in each slice will be used during the avalanche multiplication calculation Townsend & attachment coefficients vs. electric field for the gas mixture of: TFE/SF6 : 93/7 ALICE TOF General meeting, CERN – Build 29, 9 December 2009

Two di ff erent approaches are used to simulate the avalanche multiplication: ALICE TOF General meeting, CERN – Build 29, 9 December 2009

dn p (x+dx) = n e. e α.dx dn n (x+dx) = n e. e η.dx dn e (x) = n p (x) – n n (x) ALICE TOF General meeting, CERN – Build 29, 9 December 2009

 Electrons will be redistributed (Gaussian distribution) using longitudinal di ff iusion coefficient in both these approaches.  Weighting field concept is used to correctly calculate the induced signals from the movement of these charges ( I ind = E w nev ).  The induced fast signal is simulated by summation of the induced signal due to the movement of electrons in each time step from the beginning of the multiplication process until all the electrons reach to the anode.  The induced total charge is calculated by summing up all the positives ions that have been created during the multiplication process and remain in the gap after all the electrons have arrived at the anode.  For the n gap RPC, we have simply sum up the amount of the fast induced charges and the total induced charge created in each n gaps. ALICE TOF General meeting, CERN – Build 29, 9 December 2009 Positive ions Electrons negative ions Electric field

ALICE TOF General meeting, CERN – Build 29, 9 December 2009 A typical event has been chosen and 6 snapshots are shown here :

Gas mixture: 93% C 2 F 4 H 2 & 7% Sf 6 Electric field: 100 kV/cm Q F /Q T = 1/αd = 1/(126.9 × 0.025) = ALICE TOF General meeting, CERN – Build 29, 9 December 2009

designed in two stacks of five gap; A: connector for signal; B: pins for signal from cathode pads to be brought to central pcb; C: honeycomb panel; D: PCB (0.8 mm thick); E: gas gaps (0.25 mm thick); F: central PCB (1.6 mm thick); G: internal glass plates (0.4 mm thick); H: external glass plates (0.55 mm thick); I: cathode pickup pads; J: anode pickup pads. ALICE TOF General meeting, CERN – Build 29, 9 December 2009

Advantages of MRPC comparing to SRPC: The most probable value has shifted away from zero There is a well defined peak ALICE TOF General meeting, CERN – Build 29, 9 December 2009

“Recombination an important effect in MRPC” Clearly induced total charge obtained from ‘No recombination’ does not describe the data. ALICE TOF General meeting, CERN – Build 29, 9 December 2009

Di ff erent percentages of the recombination between positive and negative ions, 100 %, 97 % and 94 %, considered. This recombination has not been known until we have simulated the MRPC. ALICE TOF General meeting, CERN – Build 29, 9 December 2009

Comparison between the average simulated total and the total charge obtained from the test of ALICE 10 gap MRPC ( Akindinov, NIMA 532 (2004) ). ALICE TOF General meeting, CERN – Build 29, 9 December 2009

A simulation procedure for the development of avalanches, considering space charge in RPCs has been described and has been extended to simulate 10 gap MRPC. This simulation procedure has been encoded into a program written in FORTRAN. The experimentally observed e ffi ciencies, time resolution and the average avalanche charges can only be explained if we consider the phenomena of recombination( almost 100%). This recombination has not been known until we have simulated the MRPC. Recombination reduce the total amount of charges in the gap and this reduction is very important for the rate capability of the MRPCs. Precise study of recombination of charge carriers is going to be performed. Fast algorithm for radial electric field calculation in order to investigate the effect of this field and variation of transversal diffusion coefficient with it. Remeasuring the value of the fast/total charge for ALICE 10 gap MRPC with different percentage of SF6 and comparison with the simulated values. ALICE TOF General meeting, CERN – Build 29, 9 December 2009