Gaseous Time Projection Chambers (TPCs) have distinct advantages in a WIMP dark matter search, as well as other fields, owing to their ability to sense the highly directional nature of the signals [1,2]. How- ever, increasing the detector scale has presented technical challenges, especially electron diffusion over large drift distances. Electronegative TPC gases, such as SF6 [3] form negative ions, which show much lower levels of signal diffusion, promising increased track resolution. This improvement however, is ac- companied by low achievable gain and poor energy resolution. Efforts to improve the energy resolution have been focused on optimising electron detachment during avalanche amplification in the MPGD de- tector elements.

In this presentation I will give an overview of the CYGNUS-Oz collaboration, and discuss experimen- tal and simulation investigations focusing on negative ion detachment and avalanche. The experimental measurements make use of an upgraded CYGNUS-1 prototype gaseous TPC operating at the Australian National University. The simulation studies make use of COMSOL multiphysics field simulations and a version of Garfield++ [4], modified to simulate electronegative gases.

[1] C. Lisotti et al., arXiv:2404.03690

[2] S. Vahsen, C. O’Hare and D. Loomba, Annu. Rev. Nucl. Part. Sci. 2021. 71 189-224

[3] N.S. Phan et al., 2017 JINST 12 P02012

[4] H. Schindler, Garfield++. http://garfieldpp.web.cern.ch/garfieldpp/, Accessed: 05-06-2024