A Novel Technique for the Measurement of the Avalanche Fluctuation of a GEM Stack Using a Gating Foil

We have developed a novel technique for the measurement of the size of avalanche fluctuation using a gating device (gating foil) developed for the TPC in the future linear collider experiment. In addition to the gating function, the gating foil is capable of controlling the average fraction of drift electrons to be detected after gas amplification. The signal charge width and shape for laser irradiation as a function of the transmission rate of the gating foil can be used to determine the relative variance of gas gain. We present the measurement principle and the preliminary results obtained with a stack of Gas Electron Multipliers (GEMs).