1. MC Simulation of Micromegas Chambers Trigger Studies on NSW
Theodoros Alexopoulos, Venetios Polychronakos, George Iakovidis
MAMMA Group - Dec. 2011

2. How Our Simulation Looks Like ?
2019 events, 2020 events....were I was?
4ns....10ns ns
whatever ....
I missed the last 10 numbers....!!!

3. No.....it’s something like that .... !

4. Main Aspects - goals !
Timing Response of a Micromegas Detector for different chips (mainly focus on BNL).
APV timing simulation, BNL Chip response function integrated (three techniques).
Gas properties fully simulated with Garfield and reproduced with Garfield++.
Multiple Applications, eg Micromegas with strip pitch 250um 500um, driftGap 5mm, 9mm, different geometries ex ‘level arm’ 300mm, plain separation..etc
‘Back to Back’ Geometry simulation
Multiple Gas Mixtures, Ar:CO2 93:7, 80:20, 85:15, Ar:CF4 90:10, 95:15 and many more with diffusion analytically calculated. (Penning effects taken into account).
Theta resolution calculation
Trigger Pattern simulation, hits within 1-4 BXs, lookup tables etc.
Describe as much as possible the ionization, primary cluster, secondary electrons.
whatever else comes with it....

5. Garfield ++ http://garfieldpp.web.cern.ch/garfieldpp/ List of Gases
Garfield++ is a toolkit for the detailed simulation of particle detectors that use gas and semi- conductors as sensitive medium. The main area of application is currently in micropattern gaseous detectors.Garfield++ shares functionality with Garfield. The main differences are the more up-to-date treatment of electron transport the user interface, which is derived from ROOT.
List of Gases
ar_45_co2_15_cf4_40.gas
ar_50_ic4h10_50.gas
ar_80_co2_20.gas
ar_90_cf4_10_penning.gas
ar_90_cf4_10.gas
ar_93_co2_7.gas
ar_95_ch4_5.gasar_100.gas
ch4_100.gas
dme_50_ic4h10_50.gas
dme_90_co2_10.gas
xe_80_co2_20.gas

6. Single Chamber MC
Ionization Collisions - Probability of a Poisson-like Statistics
Cluster Size
Secondary Electrons
Avalanche Fluctuations
Cross Talk between strips from Maxwell Simulation.
Chamber Efficiency ~ 98% as measured from test beams
Electronics response

7. Ionizing Collisions
A charged particle that traverses the gas of a drift chamber leaves a track of ionization along its trajectory.
The encounters with the gas atoms are purely random and are characterised by a mean free flight path λ between ionizing encounters given by the ionization cross-section per electron σ and the density N of electrons. λ=1/(Νσ)
Therefore, the number of encounters along any length L has a mean of L/λ, and the frequency distribution is the Poisson distribution
Measured numbers of ionizing collisions per centimeter of track length in various gases
at normal density

8. Ionization Energy Loss Of Charged Particles in Gas Ar:CO2
Number of Primary Electrons not easily calculated, taken from experimental plots (linear correlation of nprim and the average atomic number.
Secondary Electrons calculated analytically.
Minimum ionizing particles in Argon NTP:
Minimum ionizing particles in CO2 NTP:

9. Primary ionization Encounters
Small number of independent events following the Poisson-like statistics.
Experimental cluster-size distributions P(k) in per cent

10. Avalanche Fluctuations Ar:CO2
probability distribution of the total number of electrons and ions in the avalanche chain which develops in a low pressure gas in a high electric field when single avalanches generate successors by photoelectric effect at the cathode.

11. Cross Talk
Maxwell Software, calculation signal cross-talk between first and second strip.
strip distance = mm strip width=0.150 mm strip pitch = mm CrossTalks - 1-2strip = 16%, 1-3 = 6%
strip distance = mmstrip width=0.400 mmstrip pitch = mmCrossTalks - 1-2strip = 9.5%, 1-3 = 3.2%

12. Theta Reconstruction Effect on single chamber
100
300
pitch 250 um
300
600
pitch 500 um
Δθ as measured per event from a single chamber with least squares for 10k of events with the same angle.

13. Theta Reconstruction Effect on single chamber large angles
Charge at first strips and especially on bigger angles is concentrated at left side of strip. Unfortunately when we reconstruct the track we take as points the center of the strips. This results in different angles.
Of course only relevant on the ‘single’ chamber track reconstruction.

14. Theta Reconstruction Effect on single chamber - small angles
Charge at first strips and especially on bigger angles is concentrated at left side of strip. Unfortunately when we reconstruct the track we take as points the center of the strips. This results in different angles.
Of course only relevant on the ‘single’ chamber track reconstruction.

15. APV 25ns trigger window (example for qThr = 2e)
First Time Above threshold of Event for 10k events before the APV 25 ns trigger window
First Time Above threshold of Event for 10k events after the APV 25 ns trigger window

16. BNL chip Signal simulation (qThr = 2e, intTime = 25ns, eThr = 0.45)
First Peak
Time above
Threshold
Maximum Peak
Time
# of e ns
First Time
Above Electronics
Threshold
Double_t qThreshold=1; //qThreshold=2e, we accept a good strip if the charge is >=2e
Double_t alpha = 1.25;// power of response function
Double_t RC = 20;// time constant of response function
Double_t electronicsThreshold = qThreshold * (TMath::Power(alpha,alpha)*TMath::Exp(-alpha));

17. BNL chip Signal simulation (qThr = 1e, intTime = 50ns)
First Times for the Maximum Peak of amplitude of Event for 10k events ns
First Times for the First Peak above threshold of amplitude of Event for 10k events ns

18. Several ‘quality’ plots

19. Small Wheel Simulation

20. Small Wheel Simulation
Four trigger techniques, first above threshold, first peak above threshold, maximum peak above threshold, mixed technique CSC-EIL trigger.
Geometry flexibility
Back to back geometry simulation
Mixed geometries and Gases
Separation
2 Drift Gaps
2 Drift Gaps
2 Drift Gaps
2 Drift Gaps
Plain Separation
Plain Separation

21. Trigger Simulation - Back To Back Chambers
MM Times
References
eg 300 1 BC 1 2 3 4

22. Angle Generation
Random Generation of
eta from ~1.3 to ~ 2.9

23. Micromegas Potential timings with Ar:CO2 93:7, 50ns, 1e

24. Micromegas Potential timings with Ar:CF4 90:10

25. Micromegas Potential timings with Ar:CH4 50:50

26. Angular resolution
Random Generation of
eta from ~1.3 to ~ 2.9

27. Trigger Schema Simulation

28. Trigger Simulation - Proposal
V. Polychronakos NSW Upgrade September 2011

29. Trigger Simulation - Proposal
V. Polychronakos NSW Upgrade September 2011

30. Trigger Simulation - Track Reconstruction within 4 BCs - Hit Patterns
Hits on SW
Pattern for LUT

31. Trigger Simulation - Track Reconstruction within 4 BCs - 2MMegas
50ns, qthr 1e
77.9 %
of events
99.9 %
of events
1.35 mrad
1.00 mrad
100 %
of events
100 %
of events
0.90 mrad
0.88 mrad

32. Trigger Simulation - Track Reconstruction within 4 BCs -
2MMegas (one each side) - 50ns, qthr 1e
82.3 %
of events
99.9 %
of events
1.37 mrad
1.03 mrad
100 %
of events
100 %
of events
0.94 mrad
0.93 mrad

33. Distance from points of fit to the line (not perpendicular)mm

34. Backup Slides

36. Avalanche Fluctuations
The dependence on N can be explained as follows. If the first ionization occurs after the electron has traveled a distance larger than the mean free path for ionization, the ionization probability per unit path length increases. Oppositely, fluctuations at larger N in the early stages of the avalanche will reduce the rate of development in the latter stages. The net effect is a reduction of the gain fluctuations.
The Polya distribution treats electrons starting the avalanche differently than the ones subsequently produced and therefore misses a clear physical interpretation. Yet, it fits the measurements of single electron response in parallel-plate detectors remarkably well. Also, measurements of very good energy resolution with detectors of different geometries can only be explained if the gain fluctuations are Polya-like. G= G= G=
VMesh <500V
θ = 2.3 ± 0.1
f = 0.30 ± 0.01
θ = 2.2 ± 0.1
f = 0.31 ± 0.01
θ = 2.3 ± 0.1
f = 0.30 ± 0.01

37. Penning Effect Ar:CO2

38. micromegas

39. Crosstalk Studies 3 strips 3 resistives
res res res3
strip strip strip3
pf/m
8.657 pf/m
pf/m
pf/m
pf/m
pf/m
pf/m
pf/m
pf/m
pf/m
Maxwell Table
Pulse - 5μΑ , width 10 ns)

40. Timing Distribution: Why has this shape ?

41. References
F.Sauli, CERN 77-09, 1977, Principles of Operation of Multiwire Proportional and Drift Chambers
Sahin, O et al. Penning transfer in argon-based gas mixtures, J. Instrum. 5 (2010) P05002 , /5/05/P05002
Instrumentation in high energy physics By Fabio Sauli
Particle detection with drift chambers - W.Blum, W. Riegler, L. Rolandi
L. G. Christophorou, D. L. McCorkle, D. V. Maxey, and J. G. Carter, "Fast gas mixtures for gas- filled particle detectors Jul.1979
T. Zerguerras et al. NIM A 608 (2009) 397.
J. Byrne, The statistical distribution of particle number in an avalanche chain, Physica, Volume 47, Issue 1, 29 April 1970, Pages 38-44, ISSN , / (70)