The LANL Sandwich Test

The Sandwich Test is a recently developed slab-variant of the copper cylinder test which, like its predecessor, is used for obtaining high explosive (HE) product equation-of-state information. A primary motivation of slab geometry is that the liner bends without stretching, making it less prone to breaking at large expansions than for cylindrical geometry. This allows a wider choice of liner materials---which need not be as ductile as copper---and also allows the liner to be made thinner. Specifically, the Sandwich Test uses a half-millimeter-thick Tantalum liner, the higher impedance of which gives a detonation state closer to c-j and a better approximation to an ideal smooth trajectory. The thin liner and the fact that pressure decays slower with axial distance in slab geometry also gives better high-pressure resolution than the cylinder test. An additional motivation is that the Sandwich Test accommodates initial temperature extremes (currently -55C to 75C) with a single test design, whereas the cylinder test would be adversely affected by differential expansion/contraction between the HE and liner. The essential design features are outlined, and the general advantages and disadvantages of the two geometries (which depend on several factors) are discussed.