Influence of ionization on the formation of plasma channel and transport of relativistic electron beam in hydrocarbon gas

The influence of ionization on the formation of plasma channel and the propagation of a relativistic electron beam in a near-critical density hydrocarbon gas are investigated by using two-dimensional (2D) particle-in-cell (PIC) simulations. A magnetic-dipole vortex is formed and self-sustained by its magnetic field pressure inside the plasma channel when the short pulse laser energy is almost depleted. After its formation, the magnetic dipole vortex moves forward with the relativistic electron beam in the plasma channel. In a fully ionized plasma, a high density plasma barrier is usually formed ahead of the plasma channel due to the density profile steepening. Therefore, the deflection of the plasma channel can easily occur during the forward movement of the magnetic dipole vortex. In contrast, the deflection of the plasma channel is suppressed by the ionization effect with hydrocarbon gas. Two main mechanisms to suppress the deflection are found. These mechanisms are the decrease of the plasma density steepening at the front of the plasma channel in a partly-ionized plasma, and the consuming of the electromagnetic field energy due to the ionization itself.