Optimization of the Design of a GEM Tracker Based on Gas Flow Simulations with COMSOL

high energy charged particles, currently under development as part of a new tracker of the high luminosity spectrometers in Hall A at Jefferson Lab. This tracker will consist of 2 small silicon microstrip planes and 6 consecutive chambers, identically made up of 3 adjacent 40x50 cm² triple-GEM modules. The continuous gas flow of an Ar/CO2 (70/30) mixture through the 2 mm gap between two GEM foils of a single module has been simulated using COMSOL’s Thin-Film Flow Model. A permanent gas flow is required inside a module to provide the expected gain and signal timing, to evacuate air that contaminates the gas mixture and to prevent fast aging of the detector due to radiation-induced chemical reactions in the gas. The gas flow should be spatially uniform in order to guarantee a homogeneous and stable detector response, e.g. in terms of efficiency. By gradual modifications of the geometry simulated in COMSOL, the design of the frame separating two GEM foils has been optimized with the aim to reach a better gas flow uniformity over the active area of the module. Modifications concern the design of the frame’s grid as well as its gas inlets and outlets. In particular, the number and size of stagnation zones have been reduced in the gas flow. The velocity field obtained for the frame configuration that has been ultimately selected is presented in the attached figures. Figure 1 presents the velocity magnitude on a linear scale, together with the computed streamlines. Figure 2 is a “Contour” plot of the velocity magnitude, with a logarithmic scale