=Paper=
{{Paper
|id=Vol-2507/246-250-paper-43
|storemode=property
|title=Realistic Simulation of the MPD Time Projection Chamber with Garfield++ Software
|pdfUrl=https://ceur-ws.org/Vol-2507/246-250-paper-43.pdf
|volume=Vol-2507
|authors=Alexander Bychkov,Oleg Rogachevsky
}}
==Realistic Simulation of the MPD Time Projection Chamber with Garfield++ Software==
https://ceur-ws.org/Vol-2507/246-250-paper-43.pdf
Proceedings of the 27th International Symposium Nuclear Electronics and Computing (NEC’2019)
Budva, Becici, Montenegro, September 30 – October 4, 2019
REALISTIC SIMULATION OF THE MPD TIME
PROJECTION CHAMBER WITH GARFIELD++ SOFTWARE
A.V. Bychkov1,a, O.V. Rogachevsky1,2
1
Joint Institute for Nuclear Research, 6 Joliot-Curie, 141980, Dubna, Moscow region, Russia.
2
Dubna State University, 19 Universitetskaya, 141982, Dubna Moscow region, Russia.
E-mail: a abychkov@jinr.ru
The detailed simulation of electron drifting in the MPD TPC was made with CERN Garfield toolkit
for the simulation of gas particle detectors. For electron transporting, the 10% Ar + 90% CH4 gas
mixture with impact of corresponding magnetic and electric fields from MPD TPC Technical Design
Report (rev. 07) were used. Ionization processes were investigated in a wire planes area near Read-Out
Chambers of the TPC. The Read-Out Chambers were modelled with some different values of gating
grid voltage.
Keywords: NICA, MPD, TPC, Time Projection Chamber, Garfield, Detector Simulation
Alexander Bychkov, Oleg Rogachevsky
Copyright © 2019 for this paper by its authors.
Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
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Proceedings of the 27th International Symposium Nuclear Electronics and Computing (NEC’2019)
Budva, Becici, Montenegro, September 30 – October 4, 2019
1. Introduction
Time Projection Chamber is a charged particle detector that performs a three-dimensional
reconstruction of particle interactions and particle trajectories. TPC’s are used in some physics
experiments in high-energy physics with large particle multiplicity. Multi-Purpose Detector (MPD) of
the NICA facility also makes use of TPC as the main detector for particle collisions reconstructions.
MPD TPC is composed of cylinder divided in two sections by the high voltage (HV) electrode
membrane. Each section has 163 cm length and 133 cm radius of drift gas volume [1]. At the endcap
of each section, there are 12 read-out chambers (ROC) to gather data of events. Gas composition that
fills drift volumes is a mixture of 90% of Argon and 10% of Methane. A detailed model with
equivalents of ROC chambers electronics and thermal screen of the MPD TPC that is used for the
current GEANT simulations for events reconstruction is shown in (fig. 1).
(a) (b)
Figure 1. Simulation Model of MPD Time Projection Chamber with ROC chambers electronics
equivalents and thermal screen
2. MPD TPC Read-Out Chambers
Twenty-four ROC chambers are used in the MPD TPC in total. Conceptual design of each
ROC chamber is conventional. A pad plane of ROC chamber contains 27 rows of pad with the size of
5x12 mm at the inner area and 26 rows of pad with size of 5x18 mm at the outer area as a compromise
of reasonable number of readout electronics channels. The pads have a rectangular shape, and the total
number of pads in the TPC is 95232 [1]. ROC chamber parameters are shown in (fig. 2(a)). A ROC
chamber has three wire grids: a gating grid, a shield grid and a sensing grid. Gating and shielding grid
wires have diameter of 75 μm, sensing grid wires diameter is 25 μm respectively. A wire structure is
shown in [fig. 3(b)]. Gating grid voltage is supposed to be -42.5V for the open gate and add ± 100V to
each wire with an alternate pattern for the closed gate.
3. TPC Simulation with Garfield++
Some parameters such as electron drift velocity, longitudinal and transverse diffusion are
necessary for realistic simulations of TPC. A Garfield++ software is used to obtain these parameters.
The Garfield++ software is a toolkit for a detailed simulation of detectors, which uses gases or semi-
conductors as a sensitive medium. Garfield++ provides: ionization calculation by a HEED program,
electric fields calculations with different mathematical techniques, transport and avalanches of
electrons by a Magboltz program [2]. 100 millions of collisions is used to calculate these parameters.
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Proceedings of the 27th International Symposium Nuclear Electronics and Computing (NEC’2019)
Budva, Becici, Montenegro, September 30 – October 4, 2019
The obtained values are 5.538 cm/μs for electron drift velocity, 0.0347 cm1/2 for longitudinal
diffusion and 0.0228 cm1/2 for transverse diffusion. Values errors are ±0.018%, ±2.5% and ±3.2%
respectively.
Gas composition Ar 90% + CH4 10%
Temperature 293.15 K (20° C)
Pressure Atmospheric + 2 mbar
Magnetic field 0.5 Tesla
Electric field 140 V/cm
HV electrode voltage -23 kV
Shielding grid (anode) voltage 0V
Sensing grid (cathode) voltage 1400 V
Gating grid voltage (expected) -42.5 V ± 100 V
(a) (b)
Figure 2. Physical parameters TPC Read-Out Chamber (a) and wire grids structure (b)
Garfield++ is utilized for calculations of electric field maps for ROC chambers and ion drift
times as well. Gating grid voltages are applied for these calculations -42.5 V for the open and -42.5 V
± 100 V for the closed gating grid accordingly. Electric fields in ROC chambers is presented in [fig.
3(a)] for the opened gating grid and in (fig. 3(b)) for the closed gating grid. Example of calculated
electron and ion drift paths is shown in (fig. 4).
Minimum value of ion drift times starts from 60 μs and maximum time is up to 800 μs for
expected gating grid voltages. Times are gathered by calculation for 104 ions paths. Signal on ROC
chamber pad plane is shown (fig. 5). Other gating grid voltages such as -42.5 V ± 250 V and -42.5 V ±
1000V are gathered for investigation purposes (fig. 6). Increasing voltage for the closed gate did not
give a significant impact on decreasing ion drift times.
Figure 3. Electric fields in ROC chambers for opened gating grid (a) and closed gating grid (b)
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Proceedings of the 27th International Symposium Nuclear Electronics and Computing (NEC’2019)
Budva, Becici, Montenegro, September 30 – October 4, 2019
Figure 4. Example of calculated electron and ion drift paths. Electron paths calculated for opened
gating grid, ion paths calculated for closed gating grid
(a) (b)
4
Figure 5. MPD TPC pad plane signal (induced current), 10 drifted ions
Figure 6. MPD TPC pad plane signal (induced current) for different closed gate voltages, 104 drifted
ions
ASIC SAMPA was adopted in Front-End Electronics [1]. Simulation of electronics response
(fig. 7) based on following transfer function [4] with parameters N = 4, sensitivity A = 20 mV/fC and
peaking time τ = 160 ns [1]:
𝑥−𝑡 𝑁 −𝑁(
𝑥−𝑡
)
𝑓(𝑥) = 𝐴 ( 𝜏 ) 𝑒 𝜏 (1)
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Proceedings of the 27th International Symposium Nuclear Electronics and Computing (NEC’2019)
Budva, Becici, Montenegro, September 30 – October 4, 2019
Figure 7. SAMPA-electronics response simulation
4. Conclusion
A detailed simulation of electrons drifting in the TPC volume is highly necessary to
investigate the performance of the MPD TPC detector. Simulation of ion drifting in ROC chambers
allows estimating the MPD TPC event rate. Electron drift parameters in Ar 90% + CH4 10% gas
composition were updated and refined for the MpdRoot software package [4, 5]. Additional
simulations of electric fields in ROC chambers and SAMPA-electronics responce help confirming
expected parameters of ROC chambers.
5. Acknowledgement
The authors thank to S.Razin and S.Movchan for constructive discussions and comments. This
work was supported by RFBR grant 18-02-40102.
References
[1] A. Averyanov, A. Bazhazhin et al. Time Projection Chamber for Multi-Purpose Detector at
NICA, Technical Design Report (rev.07) // Laboratory of High Energy Physics JINR 2018.
[2] Garfield++ software. Available at: https://garfieldpp.web.cern.ch/garfieldpp/ (accessed
10.11.2019)
[3] G. Tambave and A. Velure Qualification of the ALICE SAMPA ASIC With a High-Speed
Continuous DAQ System // IEEE Transactions on Nuclear Science June 2017, Vol. 64, no. 6.
[4] MpdRoot software. Available at: http://mpd.jinr.ru/ (accessed 10.11.2019)
[5] CERN ROOT software. Available at: https://root.cern/ (accessed 10.11.2019)
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