| GEM, Gas Electron Multiplier, is a novel detector and has been used as tracking detectors and imaging detectors because of its advantages. GEM-based TPC is proposed to be used as the central tracking detector in ILC because of the accuracy. GEM structures are rather efficient in reducing the ions drifting back to the drift volume. Ion feedback would cause space charge effect in TPCs with ensuring deformations in the electron drift trajectories. Gating-GEM where ions are blocked after electrons are avalanched by inverting the voltage is feasible in ILC-TPC. One of the issues that need to be addressed is the electron transmission efficiency of the Gating-GEM foil. It is important to improve the electron transmission efficiency when the GEM voltage is low.The definition of the electron transmission efficiency, the collection efficiency and the extraction efficiency is given in the paper. The formula of the collection efficiency and the extraction efficiency is given from the perspective of the electric flux in the theoretical analysis. Maxwell and Garfield are used in the simulation. The electric field distribution is simulated by Maxwell. The characteristics of electrons in the gas and the transport are simulated by Garfield. The electric field of the GEM hole and the transport of the electron in the GEM hole are simulated by Maxwell and Garfield. Measurements of the current of the electrodes or the energy spectrum w/o gating can be used to verify the simulation result.The effect of GEM foil geometry, gas and fields to this efficiency is studied to improve the electron transmission efficiency by simulating the transmission efficiency of the GEM foil in the paper. The best transmission efficiency can reach 80% based on the simulation. |
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