MC Simulation of Micromegas ChambersTrigger Studies on NSW

MAMMA Group - Dec. 2011

Theodoros Alexopoulos, Venetios Polychronakos, George Iakovidis

2019 events, 2019 events, 2020 2020

events....were events....were I was?I was?4ns....10ns....14ns....10ns....1

000ns000nswhatever ....whatever ....

I missed the I missed the last 10 last 10

numbers....!!!numbers....!!!

How Our Simulation Looks Like ?

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

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....

Garfield ++•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.

http://garfieldpp.web.cern.ch/garfieldpp/

ar_45_co2_15_cf4_40.gasar_50_ic4h10_50.gasar_80_co2_20.gasar_90_cf4_10_penning.gasar_90_cf4_10.gasar_93_co2_7.gasar_95_ch4_5.gasar_100.gasch4_100.gasdme_50_ic4h10_50.gasdme_90_co2_10.gasxe_80_co2_20.gas

List of Gases

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

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

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:

Primary ionization Encounters•Small number of independent events following the Poisson-like statistics.

Experimental cluster-size distributions P(k) in per cent

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.

Cross Talk•Maxwell Software, calculation signal cross-talk between first and second strip.

strip distance = 0.100 mmstrip width=0.150 mmstrip pitch = 0.250 mm

CrossTalks - 1-2strip = 16%, 1-3 = 6%

strip distance = 0.100 mmstrip width=0.400 mmstrip pitch = 0.500 mmCrossTalks - 1-2strip

= 9.5%, 1-3 = 3.2%

Theta Reconstruction Effect on single chamber

•Δθ as measured per event from a single chamber with least squares for 10k of events with the same angle.

•pitch 500 um

300

•pitch 250 um

600

300100

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.

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.

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

Maximum PeakMaximum PeakTimeTime

First PeakFirst PeakTime aboveTime aboveThresholdThreshold

Double_t qThreshold=1; //qThreshold=2e, we accept a good strip if the charge is >=2eDouble_t alpha = 1.25;// power of response functionDouble_t RC = 20;// time constant of response functionDouble_t electronicsThreshold = qThreshold * (TMath::Power(alpha,alpha)*TMath::Exp(-alpha));

First Time First Time Above Above

ElectronicsElectronicsThresholdThreshold

ns

# o

f e

BNL chip Signal simulation (qThr = 2e, intTime = 25ns, eThr = 0.45)

BNL chip Signal simulation (qThr = 1e, intTime = 50ns)

•First Times for the Maximum Peak of amplitude of Event for 10k events

•First Times for the First Peak above threshold of amplitude of Event for 10k events

ns

ns

Several ‘quality’ plots

Small Wheel Simulation

2 D

rift

Gaps

Pla

in S

epara

tion

Separa

tion

2 D

rift

Gaps

Pla

in S

epara

tion

2 D

rift

Gaps

2 D

rift

Gaps

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

Trigger Simulation - Back To Back Chambers

BC

MM

Tim

es

Refe

rence

s

1 2 3 4

1

eg 300

Angle Generation

•Random Generation of eta from ~1.3 to ~ 2.9

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

Micromegas Potential timings with Ar:CF4

90:10

Micromegas Potential timings with Ar:CH4 50:50

Angular resolution

•Random Generation of eta from ~1.3 to ~ 2.9

Trigger Schema Simulation

Trigger Simulation - Proposal

V. Polychronakos NSW Upgrade September 2011

Trigger Simulation - Proposal

V. Polychronakos NSW Upgrade September 2011

Trigger Simulation - Track Reconstruction within 4 BCs - Hit Patterns

Hits on SW

Pattern for LUT

Trigger Simulation - Track Reconstruction within 4 BCs - 2MMegas

50ns, qthr 1e

1.00 mrad

0.88 mrad0.90 mrad

1.35 mrad

77.9 % of events

99.9 % of events

100 % of events

100 % of events

Trigger Simulation - Track Reconstruction within 4 BCs - 2MMegas (one each side) - 50ns, qthr 1e

1.03 mrad

0.93 mrad0.94 mrad

1.37 mrad

82.3 % of events

99.9 % of events

100 % of events

100 % of events

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

mm

Backup Slides

θ=2.3 ± 0.1

f = 0.30 ± 0.01

G= 3.7 104

θ= 2.2 ± 0.1

f = 0.31 ± 0.01

G= 5.0 104

θ= 2.3 ± 0.1

f = 0.30 ± 0.01

G= 6.0 104

VMesh <500V

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.

Penning Effect Ar:CO2

micromegas

Crosstalk Studies3 strips 3 resistives

Maxwell Table

res1 res2 res3

strip1 strip2 strip3

14.887 pf/m8.657 pf/m

14.702 pf/m

103.11 pf/m88.656 pf/m101.98 pf/m

22.481 pf/m 22.589 pf/m

29.693 pf/m 29.634 pf/m

Pulse - 5μΑ , width 10 ns)

Timing Distribution: Why has this shape ?

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 , 1748-0221/5/05/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 0031-8914, 10.1016/0031-8914(70)90097-2.