Gas Electron Multiplier

CERN GEM (140 micron pitch, 80 micron hole diameter) on etched Kapton

The GEM is a preamplification mesh installed in front of charge collectors like MSGC. The latest GEM can boost gas gain by a factor of 1000 and with the use of mulitple GEMs, no other micropatterned gas detectors are needed to achieve high gas gain.