GEM-MIGAS Gain Optimisation for High Pressure Operation in CF4 and He/CF4 Mixtures

In this work, the GEM-MIGAS configuration was investigated to evaluate its gain properties at elevated gas pressures using CF4 and He/CF4 mixtures. The experimental work consisted of gain optimization as a function of the induction region thickness (20 to 300 mu m) using a standard GEM (50 mu m hole diameter) and an investigation on the influence of the GEM hole diameter on gain at various CF4 pressures. As expected, GEMs with narrower holes achieved higher gains, with the advantage of a lower operational voltage. For the GEM-MIGAS using a standard GEM, with 50 mu m hole diameter, the gain decrease rapidly with pressure, from 1.5 x 10(4) to 400 at 1 and 2.6 bar CF4, respectively. In contrast, the GEM-MIGAS gain drop with pressure is less steep when using a GEM with 30 mu m hole diameter, decreasing from 3.0 x 10(4) to 6.0 x 10(3) for 1 and 2.6 bar CF4, respectively. A GEM-MIGAS configuration with 50 mu m induction gap and a GEM with 30 mu m hole diameter was used in He/CF4 mixtures and yielded maximum gains of 3 x 10(3) and 2 x 10(3) for a mixture of 2.6 CF4 with 1 and 2 bar He, respectively.