Garfield simulations on Micromegas CERN Summer Student Programme

Garfield simulations on Micromegas CERN Summer Student Programme 2013 Tomohiro Yamaji SV: Theo Alexopoulos

Objectives Garfield-9/++ simulation of Micromegas(MM) ◆Objictive : Making movies which describe how MM works 　・Simple configuration(2 D, flat cathode) 　・realistic structure(3 D, cathode stripe, not perfect)

How to make movies ①Garfield-9(source code modified) 　・Avalanche simulation(Call microscopic_avalanche) 　　The default setup of garfield-9 cannot write whole electron path to output files. 　　　→source code is modified(Thanks to Mr. Kataoka) 　　　　 When any drift lines are simulated, electron path are printed. ②Manipulate output files 　・Convert the structure of output files to simple ASCII format 　・For further manipulation, digitize data and do linear interpolations 　・Rearrange data according to time series ③Drawing movies 　・Processing 2, a java-like program which is suitable for drawing pictures/movies 　　　

Movie(Simple configuration) ◆Very simple configuration 　・ 2 D, grounded wire. Flat cathode 　・primary electron starts between wires

Some features deduced from movie ◆drift property 　・electron 　　Electrons in an avalanche can reach anode by about 1 nsec 　gap between strips and mesh: 128 μm electron drift velocity in amplification region: 120μm/nsec 　・ions 　　Ions reach mesh by about 100~200 nsec 　 →Ions are one hundred slower than electrons 　　Some Ions(<10%) escape to drift region ◆apparent wrong behavior 　・amplification is very small, only about 100 　　→probably due to defects in integration parameters of microscopic method 　　 　By using AVALANCHE function, an amplification factor: ~5× 104 　 　　

Movie(more realistic)

Muon track

Backups

Avalanche amplification in amplification region ◆simulation condition 　・ 2 D Cell grounded mesh →simple wire 　・No B field ・AVALANCHE function used ◆results 　・avalanche multiplication: ~5. 5× 104

Drift velocity/Lorentz angle ◆Drift property when B fields (perpendicular to E field) are induced ・Drift velocity 　vd=4. 6919 cm/μsec @E=600 V/cm, B=0 T 　vd=4. 6299 cm/μsec @E=600 V/cm, B=0. 3 T ・Lorentz angle 　17. 2071 deg @ E=600 V/cm, B=0. 3 T