Fast simulation of avalanche and streamer in GEM detector using hydrodynamic approach

Abstract

A fast, hydrodynamic numerical model has been developed on the COMSOL Multiphysics platform to simulate the evolution and dynamics of charged particles in gaseous ionization detectors based on the Gaseous Electron Multipliers (GEM). Effects of using two-dimensional (2D), 2D axisymmetric and three-dimensional (3D) models of the detectors have been analyzed to choose the optimum configuration. The chosen model has been used to follow the entire operating regime of single, double and triple GEM detectors, including avalanche and streamer mode operations. The accumulation of space charge, its contribution towards the distortion of the applied electric field and production of streamers have been investigated in fair detail using the optimized model.

Effect of hole geometry on charge sharing and other parameters in GEM-based detectors

“…The hybrid model, on the other hand, uses HEED and MAGBOLTZ information to simulate dynamics of electron and ion species within a background neutral fluid medium utilizing the Transport of Dilute Species (TDS) interface of COMSOL. The hydrodynamic model [25,34], by its very nature, does not attempt to follow charged particles as isolated and independent (although interacting) entities. It considers the detector medium as a continuum (solvent), which a reasonable approximation, especially under normal conditions.…”

“…Next, attempts were made, following the approach described in [25], to ascertain the voltages near which transition from avalanche to streamer occurs for each of the configurations. It may be mentioned here that due to the presence of large number of charged particles and the likely importance of space charge, it is very difficult to pursue the particle model in this part of the investigation.…”

“…It is conventional to invoke a limit akin to the Raether limit [22] in order to ascertain streamer mode operation of a gaseous detector. The limit is not a fixed number, but is influenced by the structure of the detector, among other factors, as mentioned in [23][24][25]. In particular, it was mentioned in [23] that higher gain could be achieved in multiple-layer GEM-based detectors due to enhanced diffusion of electrons.…”

“…This approach has been slightly modified in the present work following the simulations carried out in [25]. In [25], it was observed that streamers occurring within a GEM hole are predominantly positive streamers in which the distortion of the applied electric field is due to the accumulation of ions, rather than electrons, within a GEM hole.…”

“…This approach has been slightly modified in the present work following the simulations carried out in [25]. In [25], it was observed that streamers occurring within a GEM hole are predominantly positive streamers in which the distortion of the applied electric field is due to the accumulation of ions, rather than electrons, within a GEM hole. This observation is also supported by the knowledge that electrons, due to their much larger drift velocity and diffusion, are more likely to get quickly transported from one location to another.…”