New Method of Isentropically Compressing Materials to Several Megabars

Abstract

IN the past, very high pressures in materials have been attained by static high-pressure techniques and dynamic shock-wave techniques. Static presses have been designed and operated to pressures up to about 500 kbar although there may be errors in the pressure scale at pressures much above 200 kbar. With shock-wave techniques it is possible to reach pressures up to 10 Mbar in dense materials such as heavy metals. Unfortunately, this technique is much less effective for more compressible materials. For example, a shock wave system which could produce a shock pressure of 10 Mbar in tungsten could only produce a pressure of about 150 kbar in liquid hydrogen. One method of circumventing these difficulties is the use of a magnetic field as a coupling medium between a sample and a metallic liner imploded by high explosives. As the pressure is essentially hydrostatic, the compressibility of the material makes little difference. Further, the buildup of pressure is relatively slow, the compression is isentropic and high pressures can be reached without the large temperature increase encountered in shock-wave experiments.