FAT-GEMs: (Field Assisted) Transparent Gaseous-Electroluminescence Multipliers

The idea of implementing electroluminescence-based amplification through transparent multi-hole structures (FAT-GEMs) has been entertained for some time. Arguably, for such a technology to be attractive it should perform at least at a level comparable to conventional alternatives based on wires or meshes. We present now a detailed calorimetric study carried out for 5.9 keV X-rays in xenon, for pressures ranging from 2 to 10 bar, resorting to different geometries, production and post-processing techniques. At a reference voltage 5 times above the electroluminescence threshold (E_EL,th∼0.7 kV/cm/bar), the number of photoelectrons measured for the best structure was found to be just 18 the same distance. The energy resolution stayed within 10 double-mesh value. An innovative characteristic of the structure is that VUV-transparency of the PMMA substrate was achieved, effectively, through TPB-coating of the electroluminescence channels combined with ITO-coating of the electrodes. This resulted in a × 2.25-increased optical yield (compared to the bare structure), that was found to be in good agreement with simulations if assuming a TPB wavelength-shifting-efficiency at the level of WLSE=0.74-1.28, compatible with expected values. This result, combined with the stability demonstrated for the TPB coating under electric field over 20 h of continuous operation, shows great potential to revolutionize electroluminescence-based instrumentation.