## 5 Outlook and Future Developments  
The overarching aim of this investigation was the assessment of a new manufacturing process for G-THGEMs, in the context for applications within large-scale LArTPCs, and potentially beyond into dark matter and medical research. Within this paper, three G-THGEMs were produced using a novel, patent pending, masked abrasive machining technique. This manufacturing method gives unprecedented versatility to the substrates and electrodes materials, together with hole shape and pattern. For the first characterisation (and comparison with an FR4 THGEM), a selection of G-THGEMs were produced with unique behaviours. Variations in glass substrate (either Borofloat 33 or fused silica) were studied, as well as two distinct hole patterns (circular or hexagonal). A transparent ITO electrode was used for all G-THGEMs. The general reported issues with current THGEM technologies in LArTPC applications can be summarised as the following: material bowing, limited stiffness and substrate thickness variations, all resulting in field non-uniformities; contamination due to the porous nature of FR4; and discharges affecting long term stability. In addition, secondary problems arise when considering quality assurance for the scale of production required for a kiloton scale experiment, such as DUNE--in particular, selection of FR4 substrates with suitable thickness variations and consistent hole formation from mechanical drilling. Furthermore, current FR4 THGEMs are unsuitable for use within the dark matter community due to inadequate substrate radiopurity. G-THGEMs have the potential to alleviate many of these concerns, while maintaining quality control and quality assurance manufacturing required for large-scale experiments. The characterisation of the G-THGEMs (compared to a conventionally manufactured FR4 THGEM) determined that for the same hole configuration, at the same bias, G-THGEMs have increased S2 light production. Furthermore, the bi-conical shape of the G-THGEM holes produced by the abrasive machining process leads to an increasing S2 light intensity over time as the G-THGEMs charge up. Cylindrical holes, typical of conventional THGEMs, result in the decrease of light intensity over time. The masked abrasive machining process allows for unprecedented customisation of G-THGEMs. The substrate, electrode, hole shape, size and pattern can all be varied, selecting for certain desirable mechanical and behavioural properties. For example, within this experiment, Borofloat 33 and fused silica glass were both investigated. Borofloat 33 is relatively low-cost, whereas fused silica is radiopure and may have the potential for use within dark matter TPCs. Both of these glasses boast flexural moduli of between 64 and 72 GPa, making them almost three times stiffer than FR4 (23 GPa). In addition, glass substrates are available with thickness variations better than \(\sim\)1.5%, a marked improvement on the typically achieved 5% for FR4 substrate THGEMs. Finally, the observed discharge behaviour of G-THGEMs was different from typical THGEMs. As ITO is resistive, discharges are localised to the region, and the amount of current flow is limited. This has an effect of quenching sparks, potentially reducing damage to the device. Additionally, carbonisation, a known problem with FR4, does not occur with glass substrates. The manufacturing technique and results discussed within this paper represent an encouraging first demonstration of the feasibility of masked abrasively machined G-THGEMs. While still in their infancy, G-THGEMs are a promising avenue for exploration. The abrasive machining technique allows for unprecedented versatility in THGEM design, allowing configurations suitable for a range of applications. Further development is ongoing, including the production of larger G-THGEMs for incorporation into dual-phase LArTPCs.