A δf Monte Carlo method to calculate plasma currents

A Monte Carlo code has been developed which efficiently calculates plasma currents by finding the deviation, f̂, of the exact distribution function, f, from the Maxwellian, FM(ψ,H), with ψ the toroidal magnetic flux enclosed by a pressure surface and H the Hamiltonian. The particles in the simulation are followed with a traditional Monte Carlo scheme consisting of an orbit step in which new values for the positions and momenta are obtained, and a collision step in which a Monte Carlo equivalent of the Lorentz operator is applied to change the pitch of each particle. The δf code was used to study the aspect ratio and collisionality dependence of the bootstrap and two Fourier components of the Pfirsch–Schlüter current. The δf code is about 104 times as efficient as other Monte Carlo techniques used to calculate currents in plasmas.