The propagation of a high current relativistic electron beam through a dense plasma, for example, in fast-ignition inertial confinement fusion, produces strong heating and magnetic field generation. The j × B force and thermal pressure gradient that the return current creates may in fact cavitate and cause shock waves in the plasma around the electron beam.Here we investigate this effect in different regimes of plasma density and hot electron current. An analytic model has been developed that gives good estimates of the density, pressure, magnetic field and velocity obtained in the plasma. This model is compared against the results from an MHD code that includes the effects of resistive field growth, Ohmic heating and the j ×B force. The strength of the cavitation is found to be dependent upon the ratio between j 2 and the initial mass density. It is shown that cavitation is indeed relevant to fast-ignition, and is strong enough to launch shocks in certain circumstances.
Abstract. When intense short-pulse laser beams (I > 10 22 W/m 2 , < 20 ps) interact with high density plasmas, strong shock waves are launched. These shock waves may be generated by a range of processes, and the relative signifi cance of the various mechanisms driving the formation of these shock waves is not well understood. It is challenging to obtain experimental data on shock waves near the focus of such intense laser-plasma interactions. The hydrodynamics of such interactions is, however, of great importance to fast ignition based inertial confi nement fusion schemes as it places limits upon the time available for depositing energy in the compressed fuel, and thereby directly affects the laser requirements. In this manuscript we present the results of magnetohydrodynamic simulations showing the formation of shock waves under such conditions, driven by the j × B force and the thermal pressure gradient (where j is the current density and B the magnetic fi eld strength). The time it takes for shock waves to form is evaluated over a wide range of material and current densities. It is shown that the formation of intense relativistic electron current driven shock waves and other related hydrodynamic phenomena may be expected over time scales of relevance to intense laser-plasma experiments and the fast ignition approach to inertial confi nement fusion. A newly emerging technique for studying such interactions is also discussed. This approach is based upon Doppler spectroscopy and offers promise for investigating early time shock wave hydrodynamics launched by intense laser pulses.
Motivated by the shock ignition approach to improve the performance of inertial fusion targets, we make a series of studies of the stability of shock waves in planar and converging geometries. We examine stability of shocks moving through distorted material and driving shocks with nonuniform pressure profiles. We then apply a fully 3D perturbation, following this spherically converging shock through collapse to a distorted plane, bounce and reflection into an outgoing perturbed, broadly spherical shock wave. We find broad shock stability even under quite extreme perturbation. V C 2014 AIP Publishing LLC. [http://dx
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