Cavitation and shock wave formation in dense plasmas by relativistic electron beams

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 x 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 x B force. The strength of the cavitation is found to be dependent upon the ratio between j2 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.