Characterisation of Large Area THGEMs and Experimental Measurement of the Townsend Coefficients for CF$_4$

TL;DR

This paper investigates the scaling challenges of large-area THGEM detectors, experimentally measures Townsend coefficients for CF$_4$, and evaluates their performance and applications in dark matter detection and nuclear security.

Contribution

It provides the first experimental measurement of Townsend coefficients for large-area THGEMs in CF$_4$ and assesses their geometrical imperfections and performance in underground environments.

Findings

Large area THGEMs show expected gain consistent with small-scale data.

Geometrical imperfections in large THGEMs were quantified and characterized.

Simulations suggest potential for use in directional dark matter detection and nuclear security.

Abstract

Whilst the performance of small THGEMs is well known, here we consider the challenges in scaling these up to large area charge readouts. We first verify the expected gain of larger THGEMs by reporting experimental Townsend coefficients for a 10 cm diameter THGEM in low-pressure CF$_4$. Large area 50 cm by 50 cm THGEMs were sourced from a commercial PCB supplier and geometrical imperfections were observed which we quantified using an optical camera setup. The large area THGEMs were experimentally characterised at Boulby Underground Laboratory through a series of gain calibrations and alpha spectrum measurements. ANSYS, Magboltz and Garfield++ simulations of the design of a TPC based on the large area THGEMs are presented. We also consider their implications for directional dark matter research and potential applications within nuclear security.