A Novel Manufacturing Process for Glass THGEMs and First Characterisation in an Optical Gaseous Argon TPC

Abstract

This paper details a novel, patent pending, abrasive machining manufacturing process for the formation of sub-millimetre holes in THGEMs, with the intended application in gaseous and dual-phase TPCs. Abrasive machining favours a non-ductile substrate such as glasses or ceramics. This innovative manufacturing process allows for unprecedented versatility in THGEM substrates, electrodes, and hole geometry and pattern. Consequently, THGEMs produced via abrasive machining can be tailored for specific properties: for example, high stiffness, low total thickness variation, radiopurity, moisture absorption/outgassing and/or carbonisation resistance. This paper specifically focuses on three glass substrate THGEMs (G-THGEMs) made from Schott Borofloat 33 and fused silica. Circular and hexagonal hole shapes are also investigated. The G-THGEM electrodes are made from indium tin oxide (ITO), with a resistivity of 150 Ω/Sq. All G-THGEMs were characterised in an optical (EMCCD) readout GArTPC and compared to a traditionally manufactured FR4 THGEM, with their charging and secondary scintillation (S2) light production behaviour analysed.

Scintillation of Ar/CF4 mixtures: glass-THGEM characterization with 1% CF4 at 1–1.5 bar

“…The substrate (1 mm thick) of the bottom THGEM was made from Schott Borofloat 33, whilst that of the top THGEM was from fused silica. In both cases, the electrodes were made from an indium tin oxide (ITO) coating on the substrate [9]. Once the electrons released by ionizing particles arrive at the THGEMs, they experience a high electric field emanating from the holes.…”

“…With this in mind, a systematic study of the optical gain of a double glass-THGEM stack [9] was performed in argon doped with 1% CF 4 at around atmospheric pressure. The characterization was carried out using an alpha source and, when good amplification and transfer fields had been determined, imaging of cosmic radiation was performed.…”

ARIADNE+: Large scale demonstration of fast optical readout for dual-phase LArTPCs at the CERN Neutrino Platform

“…The extraction grid is mounted 15mm from the 50x50cm glass THGEMs. Liverpool University patent approved glass THGEMs [3] have increased rigidity over FR4 THGEMs, vital for area sizes such as these within ARIADNE + , and feature 'hour-glass' shaped holes which collect charge over time and increase light output at lower biases than FR4 THGEMs. For the three quadrants with Timepix3 cameras imaging visible light, situated above the THGEMs is a PEN film-coated glass.…”

Novel electron and photon recording concepts in noble-liquid detectors

“…Note that GEM and THGEM electrodes are produced over large area by the printed-circuits industry; large-area COBRA-like structures can most probably be produced in similar ways. An important recent development is the glass-made THGEM (G-THGEM), within the ARIADNE optical-TPC project [91]. So far, borofloat 33 glass and fused silica glass electrodes (the latter of higher radiopurity) were produced by abrasive formation of sub-mm holes.…”

“…to form COBRA-like patterns. While current G-THGEM electrodes for ARIADNE reach sizes of 50 × 50 cm 2 , the technology can be extended to larger dimentions and to other glass types [91].…”