Speakers
Description
In the context of CYGNUS consortium R&D work towards large scale direction sensitive detectors for dark matter and nucleus-neutrino coherent scattering experiments, we present gain and functionality results on the use of new high gain MM-ThGEM charge amplification devices with negative ion SF$_6$, CF$_4$ and SF$_6$:CF$_4$:He mixtures towards atmospheric pressure. The device is designed for operation with micromegas or other 2D charge readout planes. Results show stable operation with high gains in various mixtures including low pressure operation. In addition a new molecular sieve-based gas recycling system is presented that provides for simultaneous removal of both radon and common impurities from SF$_6$:CF$_4$:He gases in TPCs, hence minimising the total amount of gas required. Removal of internally-produced radon and associated progeny is important for background suppression whilst removal of outgassing and leaked-in contaminants such as water, oxygen and nitrogen is required to suppress capture of interaction-produced electrons which causes gain suppression. The system utilises a Vacuum Swing Adsorption (VSA) technique, allowing continuous long-term operation. Studies are presented of a new low radioactive molecular sieve, developed for this work and found to emanate radon up to 98% less per radon captured than commercial material.
