  We further study the performance of single, double and triple Gas Electron
Multiplier (GEM) detectors in pure noble gases at high pressures, in the range
of 1-10 atm. We confirm that light noble gases, in particular He and its
mixtures with Kr, have the highest gain, reaching 10^6, and an unusual gain
dependence on pressure. Effects of the number of GEMs, GEM hole diameter and
pitch are investigated in detail. In He, avalanche-induced secondary
scintillations are observed at high gains, using the metal photocathode. These
results are relevant in the field of avalanche mechanism in noble gases and
X-ray, neutron and cryogenic particle detectors.
