Particle Loading for a Plasma Shear Layer in a Magnetic Field

Some new particle loading methods have been developed for use in simulating a plasma shear layer with nonuniform density and temperature in the presence of a magnetic field, especially with a large effective ion gyroradius. The numerical approach to the shear instability with strong velocity shear consists of starting a simulation from a state of equilibrium, perturbing this equilibrium in some way, then observing the linear growth of the perturbation and its ultimate saturation.

With the usual particle loading method, it is difficult to reproduce the equilibrium state if the ion gyroradius is not small on the scale of the shear. The reason is that, with nonuniform velocity shear, i.e., with the nonuniform E-field, a particle may have more than one guiding-center, the particle distribution cannot be obtained analytically, and it may need to be evaluated numerically.

If an equilibrium state is not achieved in the particle loading, the shear may relax by means of an "artificial instability" in the course of the simulation, obscuring the physics of interest. With the particle loading method here presented, we simulate a shear layer in a state close to equilibrium without having to solve the Vlasov-Boltzmann equation.