GEM-MIGAS Gain Optimisation for High Pressure Operation in CF$_{4}$ and He/CF$_{4}$ Mixtures

In this work, the GEM-MIGAS configuration was investigated to evaluate its gain properties at elevated gas pressures using CF
$_{4}$
and He/CF
$_{4}$
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 CF
$_{4}$
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
$1.5 \times 10^{4}$
to 400 at 1 and 2.6 bar CF
$_{4}$
, 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
$3.0 \times 10^{4}$
to
$6.0 \times 10^{3}$
for 1 and 2.6 bar CF
$_{4}$
, respectively. A GEM-MIGAS configuration with 50
$\mu$
m induction gap and a GEM with 30
$\mu$
m hole diameter was used in He/CF
$_{4}$
mixtures and yielded maximum gains of
$3 \times 10^{3}$
and
$2 \times 10^{3}$
for a mixture of 2.6 CF
$_{4}$
with 1 and 2 bar He, respectively.