Plasma Flow in a Laser Target as Used in the CRASH Project and its Sensitivity to the Equation-of-State for Non-Ideal Plasmas and a Warm-Dense Matter

Igor Sokolov
University of Michigan

A xenon plasma flow in a laser target as used in the Center for RAdiative Shock Hydrodynamics (CRASH) incorporates the strong shock wave (see [1]). A high-energy-density in xenon at the pressure about 1 Barr, is generated using a ten-beams channel of the Omega laser, the total energy of the laser shot being ~4 kJ. Under these circumstances the shocked xenon intensely radiates the X-ray emission.
It is known from numerous studies of the strong explosions in the atmosphere that the strongly radiating shock wave while sliding along the solid surface (in the discussed application this is the ground surface) may suffer a significant reconstruction of its shape, which phenomenon is called the Taganov effect. On having been emitted from the shock-heated gas behind the shock wave front, the radiation heats up the perfectly opaque solid surface. As the result, the temperature of the air layer adjacent to the ground surface grows up due to heat conduction. The shock wave may propagate along this layer at the speed greater than that for the shock wave propagation along the unperturbed xenon, resulting in an essentially non-planar shape of the shock front, with a runaway precursor.
In the laser targets as used in the CRASH project the flow configuration may occur which is physically similar to that accompanying the Taganov effect. The X-ray radiation emitted from the shocked xenon is then absorbed in the plastic wall of a cylindrical gas-filled capilary, along which the shock wave propagates. The radiation fluxes are so intense, that well prior to the shock wave arrival the wall material is heated upeV temparatures. The ablation of the wall material occurs to converge towards the axis of symmetry, forming as the result the convergent conical shock wave in xenon. Similarly to what happens in the course of the Taganov effect, the interaction of this convergent wave with the original shock wave as propagating along the capillary may modify the shock wave geometry
The easily observable in the experiment as well as in the numerical simulations, the modification of the shock wave configuration appears to be sensitive to the choice of the equation of state for the wall material. In the present work we compare the variants of the numerical simulation of the flow in the CRASH target with the use of different equations of state for the wall material (polyimide) The choice of the EOS which is in the best agreement with the experiment may allow to choose the better model for a plastic under the conditions when the material is not only a non-ideal plasma, but it is also a “warm dense matter” (WDM) The numerical models for the equation of state and opacities are provided by several groups from Russia, USA, France and Switzerland. Numerical simulations are preformed within the approximation of radiation hydrodynamics with multi-group diffusive radiation transport.
[1]R.P.Drake et al, High Energy Density Physics, 7(1), 130-140 (2011)

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