Parallel Magnetic Field Spatial Resolution Micromegas Weekly - PowerPoint PPT Presentation

Garfield Simulation: Electron Diffusion in a Parallel Magnetic Field – Spatial Resolution Micromegas Weekly 10.09.13 Jona Bortfeldt – LMU Munich 10.09.13 Jona Bortfeldt 1

Reminder: Influence of parallel B-field on Cluster Width? (-> Spatial Resolution, Discharges , … ) • B-field parallel to drift field „ guides “ the electrons and suppresses transverse diffusion • how large is the influence on the cluster width? • in NSW B < 0.3T simple Garfield simulation: • 2 dimensional; 5mm drift region , 128μm amplification region, homogeneous readout plane • mesh replaced by wires, no penning transfer → gas gain approximate • planar diffusion correct • 1000 pions with 130GeV at perpendicular incidence • two methods to determine the event width: • last hit strip – first hit strip → total width • Gaussian fit to resulting charge distribution → standard deviation 10.09.13 Jona Bortfeldt 2

Calculation of Spatial Resolution • assign charge detected within 250µm to a single strip 𝑡𝑢𝑠𝑗𝑞 ×𝑑ℎ𝑏𝑠𝑕𝑓(𝑡𝑢𝑠𝑗𝑞) 𝑏𝑚𝑚 𝑡𝑢𝑠𝑗𝑞𝑡 • calculate charge-weighted mean: 𝑑ℎ𝑏𝑠𝑕𝑓(𝑡𝑢𝑠𝑗𝑞) 𝑏𝑚𝑚 𝑡𝑢𝑠𝑗𝑞𝑡 • calculate residual = reconstructed hit – expectation • fit residual distribution from 1000 tracks with single Gaussian what this simulation can and cannot do:  determine influence of diffusion on spatial resolution  show influence of B field on diffusion X model electron mesh transparency (relevant for small and very large drift fields) X determine influence of gas gain = pulse height on spatial resolution (not a large influence anyway) X model capacitive coupling between strips and charge distribution (charge distribution on strips not as smooth as in reality)

Comparison of Simulation and Experiment – Spatial Resolution for Ar:CO 2 85:15 measured spatial resolution Bortfeldt et al. NIM A 718 406-408 • similar trends visible except for small fields • deviation: mesh transparency not modeled correctly • offset: capacitive/inductive coupling not considered

Comparison of Simulation and Experiment – Spatial Resolution for Ar:CO 2 93:7 • similar behavior visible • offset: capacitive/inductive coupling not considered

Simulated Spatial Resolution for different B fields consider spatial resolution at fixed drift field (no change in mesh transparency) → reduced diffusion improves spatial resolution 10% reduction for B ≤ 0.4T 15% reduction for B ~ 0.6T 25% reduction for B ~ 1T

Simulated Spatial Resolution for Different Strip Periodicities • for larger strip pitch, reduced diffusion also improves spatial resolution • „jump“ between 400µm pitch and 500µm pitch due to not considered capacitive/inductive coupling

Summary • spatial resolution has been determined from simple Garfield simulation • trends for spatial resolution vs drift field for Ar:CO 2 93:7 and 85:15 are reproduced by simulation • influence of B field on spatial resolution can be extracted from simulation • parallel B field → reduced diffusion → improved spatial resolution • deviation: mesh transparency, gas gain, capacitive/inductive coupling not modeled correctly • results should be cross checked with a more advanced simulation Thank you!

backup: simulated cluster width for different magnetic fields total width sigma from Gaussian fit for B≤0.4T: ~10% variation, for 0.6T ≤ B ≤ 0.8T: ~15% reduction, for B=1T: ~20% reduction 10.09.13 Jona Bortfeldt 9

backup transverse diffusion for angle(E,B) = 0 degrees 10.09.13 Jona Bortfeldt 10