Gain properties of gas electron multipliers (GEMS) for space applications

Fine-pitch and thick-foil GEMs have been produced using a laser etching technique for photoelectric X-ray polarimeters onboard future missions. The finest hole pitch of the thick-foil GEM is 80 mu m with a hole diameter of 40 mu m, and a thickness of the insulator is 100 mu m. The maximum effective gain in a 70%-30% mixture of argon and carbon dioxide reaches 3 x 10(4) at voltage of 750 V between GEM electrodes. No significant gain increase or decrease was observed during 24 hours test in which applied high voltage was ramped tip and down frequently. The measured gain stability was less than 4%. An accelerated test of the high voltage ramp up and down for two years LEO operations were carried out. During the 6500 times voltage ramp up and down, the GEM kept its gain within 4% variation and no unexpected behavior was observed.