Collision-driven negative-energy waves and the weibel instability of a relativistic electron beam in a quasineutral plasma.

A new model describing the Weibel instability of a relativistic electron beam propagating through a resistive plasma is developed. For finite-temperature beams, a new class of negative-energy magnetosound waves is identified, whose growth due to collisional dissipation destabilizes the beam-plasma system even for high beam temperatures. We perform 2D and 3D particle-in-cell simulations and show that in 3D geometry the Weibel instability persists even for collisionless background plasma. The anomalous plasma resistivity in 3D is caused by the two-stream instability.

Merging of super-Alfvénic current filaments during collisionless Weibel instability of relativistic electron beams.

The theoretical framework predicting the long-term evolution, structure, and coalescence energetics of current filaments during the Weibel instability of an electron beam in a collisionless plasma is developed. We emphasize the nonlinear stage of the instability, during which the beam density of filaments increases to the background ion density, and the ambient plasma electrons are fully expelled from the filaments. Our analytic and numerical results demonstrate that the beam filaments can carry super-Alfvénic currents and develop hollow-current density profiles. This explains why the initially increasing magnetic field energy eventually decreases during the late stage of the instability.

Self-consistent system of equations for a kinetic description of the low-pressure discharges accounting for the nonlocal and collisionless electron dynamics.

In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study, a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is derived. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. The importance of accounting for the nonuniform plasma density profile on both the current density profile and the EEDF is demonstrated.