The inert gases Ar, Xe, and He as cryogenic pressure media

We have investigated the inert gases Ar, Xe, and He for suitability as pressure media in a diamond anvil cell at liquid-helium temperature, from 0 to 30 kbar, and compared these with a 4:1 methanol/ethanol mixture. Xe gives severe nonhydrostaticity and is of no value as a low-temperature medium. Ar gives much less nonhydrostaticity, but little improvement over the 4:1 methanol/ethanol mixture. He gives no observable nonhydrostaticity even when the pressure is changed at low temperature. A technique for loading with He is presented.