Impact of GEM foil hole geometry on GEM detector gain
Detailed 3D imaging of Gas Electron Multiplier (GEM) foil hole geometry was realized. Scanning White Light Interferometry was used to examine six topological parameters of GEM foil holes from both sides of the foil. To study the effect of the hole geometry on detector gain, the ANSYS and Garfield ++ software were employed to simulate the GEM detector gain on the basis of SWLI data. In particular, the effective gain in a GEM foil with equally shaped holes was studied. The real GEM foil holes exhibited a 4% lower effective gain and 6% more electrons produced near the exit electrode of the GEM foil than the design anticipated. Our results indicate that the GEM foil hole geometry affects the gain performance of GEM detectors.
The operational experience of the triple-GEM detectors of the LHCb muon system: Summary of 2 years of data taking
The LHCb muon system consists of more than a thousand gas detectors, mostly MWPC, located in five different stations. The muon detector is used to define the muon trigger and to identify muons at the high-level triger and at the reconstruction stage. The first station of the muon detector, located in front of the calorimetric system, is made of 274 chambers. The 12 most irradiated chambers, the ones closer to the beam pipe, are double triple-GEM detectors with pad readout. These detectors have an active area of 200×240 mm2 and are routinely operated at rates close to 300 kHzlcm2. With the gas mixture used (Ar/CO22/CF4 at 45/15/40) these detectors have the requested efficiency (>96% in a 20 ns time window for the logical OR of the two sensitive gaps) when operated at gains of about 4300. In this presentation we will report on the performance of these 24 triple-GEM detectors after more than 2 years of operation in the harsh LHCb conditions. We will also show some problems occurred during data taking, in particular on the failure of a few GEM foils following repeated discharge phenomena, and the solutions implemented to reduce the occurrence of such problems.
Miniband formulation in Ge/Si quantum dot array
In this work, we estimate the coupling effect of miniband structure and density of states (DoS) resulting from different qunatum-dot physical parameters in a well-aligned Ge/Si quantum dot (QD) array fabricated by neutral beam etching technology. The density of QDs dominates the coupling effect and miniband’s bandwidth, the radius of QDs affects the magnitude of energy levels and miniband bandwidth, and the thickness of QDs has a great impact on the magnitude of energy levels. Among the different shapes of Ge/Si QDs, discoid QDs exhibit the most band crossing and broadest bandwith under the same physical parameters.