GEM-MIGAS Electron Multiplier Operation in Argon-Methane Mixtures
A Gas Electron Multiplier with a Micro-Induction Gap Amplifying Structure (GEM-MIGAS) is formed when a conventional GEM is operated with a short induction gap, typically 50 mum. A three-dimensional electric field simulation of a GEM-MIGAS detector was performed in order to evaluate the electric field profile in the different regions of the structure. Different electrostatic conditions were undertaken to forecast the detector performance in gas medium. An experimental study of GEM-MIGAS operating in an Ar/CH4 (90/10%) gas mixture, in pure CH4 and in pure Ar was carried out. Performance characteristics including charge gain and energy resolution for 5.9 keV X-rays are presented.
GEM-MIGAS: Charge gain characteristics for the induction gap in the 50–300 μm range
Abstract A conventional gas electron multiplier with its induction gap set around 50 μm results in a two stage electron amplification device called the gas electron multiplier with micro-induction gap amplifying structure (GEM-MIGAS). We present results on the charge gain characteristics of GEM-MIGAS induction gap as a function of induction gap thickness, using the single electron response method. In the present study, the induction gap was varied between 50 and 300 μm and the GEM-MIGAS was operated in gas flow mode using He/iso-C 4 H 10 (85/15%). The charge gain response agreed well with the classical parallel plate gain formula. From the experimental data, it was possible to derive the approximate values of the ionisation potential threshold and the ionisation mean free path, which exhibits an approximately linear dependence on the induction gap thickness. The optimum gap thickness region, where the charge gain was at a maximum for a given induction voltage and where it was least sensitive to variations in the gap thickness, was found to be in the 50–70 μm range. Nevertheless, the highest charge gains, achieved before the onset of detector instabilities, were obtained with the gap thickness set between 150 and 300 μm with values reaching the 10 6 region, owing to the higher voltages that can be applied to the device.
Thick GEM-like multipliers—a simple solution for large area UV-RICH detectors
We report on the properties of thick GEM-like (THGEM) electron multipliers made of 0.4 mm thick double-sided Cu-clad G-10 plates, perforated with a dense hexagonal array of 0.3 mm diameter drilled holes. Photon detectors comprising THGEMs coupled to semi-transparent CsI photocathodes or reflective ones deposited on the THGEM surface were studied with Ar=CO2 (70:30), Ar=CH4 (95:5), CH4 and CF4. Gains of � 10 5 or exceeding 10 6 were reached with single- or double-THGEM, respectively; the signals have 5–10 ns rise times. The electric field configurations at the THGEM electrodes result in an efficient extraction of photoelectrons and their focusing into the holes; this occurs already at rather low gains, below 100. These detectors, with single-photon sensitivity and with expected sub-millimeter localization, can operate at MHz=mm 2 rates. We discuss their prospects for large-area UV-photon imaging for RICH.