Triple GEM operation in compressed He and Kr

We study the performance of the triple gas electron multiplier (GEM) detector in pure noble gases, He and Kr, at high pressures, varying from 1 to 15 atm. The operation in these gases is compared to that recently studied in Ne, Ar and Xe. It turned out that light noble gases, He and Ne, have superior performances: the highest gain, approaching 105, and an unusual gain dependence on pressure. In particular, the maximum gain in He and Ne does not decrease with pressure, in contrast to Ar, Kr and Xe. These results are relevant for understanding the basic mechanisms of electron avalanching in noble gases and for applications in cryogenic particle detectors, X-ray imaging and neutron detectors.