Mircomegas - Gas gain simulation studies -

Goals of the gas gain studies Comparison of amplification-factors with experimental Data Measurements will be done in Jan/Feb 2013 at the LMU Munich for non resistive chambers (resistive chambers depend on availability) Voltage Scan from 480V to ? 550V ? Upper boarder of the voltage scan depends on CPU capaticity, and efficiency of the code, finals value not jet settled Dependence on: temperature (Simulation & Experimental Data available) pressure ( ‘’ ) Layout of the simulated mesh Test of a CPU optimized algorithm (p. 6) Avalanche profiles (ne/z; x-y distribution /z) 26. Nov 2012 Goals of the gas gain studies

Simulating a MM mesh Woven structure of the mesh causes increase in CPU time, due to: More complex meshing in 3D models using FEM (ANSYS) More and smaller elements using neBEM (Garfield) No analytic calculation of the field possible Question: Is that effort necessary? Or: Do more simple layouts result in the same distribution? Microscope-photo of a mesh 26. Nov 2012 Simulating a micromegas mesh

Simulating a MM mesh Properties to simulate: periodic mesh pitch cylindrical wires woven mesh structure mesh flattening (flattened tops, compressed contacts) X Microscope-photo of a mesh planar approximation flat - cubic elements flat - cylindrical elements woven - torodial elements 26. Nov 2012 Simulating a micromegas mesh

Simulating a MM mesh Contours of the potential flat - cubic elements flat - cylindrical elements Contours of the potential woven - torodial elements @ y =0 Mesh: upper edge lower edge Contours of the potential woven - torodial elements @ y =pitch/2 26. Nov 2012 Simulating a micromegas mesh

Idea for a CPU optimized simulation Divide the avalanche simulation in two steps, by insertion of a “virtual” plane @ ~ half distance: 1.) - between mesh & virtual plane - inhomogeneous field due to mesh geometrie - crucial part of the avalanche formation with a smaller number of electrons (< 103) microscopic avalanche calculation in Garfield 2.) - between virtual plane & readout strips - highly statistical part (105 - 106) in an approx. homogeneous field using a parameterized function for each electron at the plane, assuming a uniform field 1 2 26. Nov 2012 CPU optimized simulation

Idea for a CPU optimized simulation Open questions concerning in this method: Where to insert the “virtual” plane? (trade-off: enough electrons after step 1 to obliterate the statistic fluctuation in step 2 vs. CPU cost) - Minimum number of electrons in the avalanche? (= minimum voltage) - How severe is the effect of ignoring space charge effects in step 2? Method will be tested in a mid range voltage and if successful used to simulate higher voltages. 1 2 26. Nov 2012 CPU optimized simulation

Open questions Other parameters of interest? Which dependences to study? (temperature, pressure, gas mixture?) Range of the voltage scan? (depends on success or not with CPU saving method) How to take resistive strips into account? - full simulation in Garfield++ - Using signal from non-resistive simulation + LTSpice 26. Nov 2012 Open questions