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.
Ion Back-Flow Suppression in GEM-MIGAS
The Gas Electron Multiplier with a MIcromegas Gap Amplifying Structure (GEM-MIGAS) is obtained by the coupling of a GEM to a short induction gap, typically 50 μm , where additional charge multiplication occurs. In this work, the GEM-MIGAS gain and ion back-flow are investigated, for induction regions in the range of 50-300 μm. The studies were carried out with a GEM-MIGAS coupled to a semitransparent CsI-photocathode operated in Ar/5%CH4 gas mixture at atmospheric pressure. The increase of the induction gap thickness from 50 μm to 300 μm leads to an increase of the maximum achievable charge gain by a factor of 100, from ~ 2 × 103 to ~ 2 × 105. Moreover, the high field ratio between amplification and conversion regions, which prevents ions to drift towards the conversion region, allows a strong reduction, by a factor ~ 20, of the ion back-flow ratio to the drift region, when compared with the operation in GEM-mode (i.e. at low induction field). For typical drift fields of 0.1 and 0.5 kV/cm, an ion back-flow fraction ~ 1% and ~ 4%, respectively, was obtained for the corresponding charge gains of ~ 5 × 104 and ~ 2 × 105, respectively.
New developments and future perspectives of gaseous detectors
Gaseous detectors are fundamental components of all present and planned high energy physics experiments. Over the past decade two representatives (GEM, Micromegas) of the Micro-Pattern Gas Detector (MPGD) concept have become increasingly important; the high radiation resistance and excellent spatial and time resolution make them an invaluable tool to confront future detector challenges at the next generation of colliders. Novel structures where GEM and Micromegas are directly coupled to the CMOS multi-pixel readout represent an exciting field and allow to reconstruct fine-granularity, two-dimensional images of physics events. Originally developed for the high energy physics, MPGD applications have expanded to astrophysics, neutrino physics, neutron detection and medical imaging.