R&D in new detector technology for the upgrade of the muon system in CMS
The CMS collaboration is planning to extend its current muon detection capabilities in the forward region with new detector devices based on Gas Electron Multiplier (GEM) technology. In the high luminosity scenario LHC will produce a flux of particle of about 10E4-10E5 Hz/cm2 therefore good signal to noise separation is required. GEM detector offer a fast signal response (~6ns), good spatial resolution and a uniform efficiency throughout the detector area.
A GEM detector is a thin metal-clad polymer foil chemically perforated by a high density of microscopic holes. The GEM foil is clad on both sides with a thin conductive layer of copper. A voltage of a few hundred volts is applied between the two layers which creates a strong electric field. An incident high energy charged particle will interact with the gas molecules and ionize some of them. The electrons extracted gain kinetic energy, thanks to the high electric field inside the holes, and ionize further molecules leading to an electron avalanche that propagates to the anode at the bottom of the detector where appropriate electronics is used to measure the induced signal.
Extensive simulation studies are required in order to optimize the detector design in terms of dimensions, type of gas, gain uniformity and possible mechanical deformation effects which may affect the detector performance. It has been few years that the TAMUQ group leads the simulation efforts to optimize the different muon detector upgrades at the LHC, our studies include:
- Simulation of signal induction in a triple-GEM detector (GARFIELD simulation)
- Simulation of mechanical deformation in GEM foils and impact on detector performance (ANSYS and GARFIELD simulations)
- Simulation of charged particles traversing the detector (GEANT4 simulation)
- Simulation of radiation environment for the high luminosity LHC scenario (FLUKA simulation)
- estimation of the sensitivity of the GEM detector to background particles (neutron and photons)
Mechanical Deformation of GEM foils under large deformation and stretching
The production of GEM foils is conducted by independent contractors. The holes are produced by a chemical etching process, however, some small imperfections in the shape could degrade the detector performance. In addition to the chemical etching, the foils might suffer deformation due to the mechanical stretching process. Both mechanical deformations can be simulated in order to understand the impact on the detector performance.
We conduct extensive Finite Element Modeling (FEM) to quantify the effect of the stretching forces on the GEM foil by studying the mechanical strain-stress curve.
ACK: all computational resources, 3D visualization tools and scientific software are provided by the Research Computing at TAMUQ.