Doubly-shocked helium.

McClintock, Peter V. E. (1985) Doubly-shocked helium. Nature, 313 (5999). p. 181.

Abstract

In experiments carried out by W.J. Nellis and colleagues at Lawrence Livermore National Laboratory in California, and reported in Physical Review Letters 53, 1248;1984, liquid helium has been shock-compressed to densities of up to five times that of the normal liquid. The pressure transiently achieved in the experiments approaches that to which helium is subjected on some planets.