STUDY OF THE DIFFUSION ACROSS A MAGNETIC-FIELD IN A BEAM-PLASMA INTERACTION USING A DRIFT-KINETIC VLASOV CODE

A drift-kinetic Eulerian Vlasov code, with fluid equations for the ion s, is developed to study the problem of the injection of an electron b eam into a two-dimensional magnetized plasma, often referred to as dir ect current (dc) helicity injection. The diffusion of electrons across a magnetic field in the presence of a beam-plasma instability is stud ied. The case of a magnetic field tilted with respect to the beam dire ction is considered. The competition between the velocity shear Kelvin -Helmholtz (KH) and the beam-plasma (BP) instabilities is investigated in order to analyze the plasma heating and current drive mechanism in duced by the beam injection. The KH instability generates low-frequenc y plasma convection motion associated with cEXB/B-2 drift. In particul ar, the diffusion coefficients D-y and D-v parallel to describing, res pectively, the anomalous diffusion process induced in space across the magnetic field by the KH instability, and the velocity diffusion proc ess due to the kinetic effects induced in velocity space along the mag netic field by the BP instability, are computed using test-particle di agnostics. In the present Cartesian model, it is found that D-y = D-v parallel to tan(2) theta/omega(ce)(2) where theta is the angle between the magnetic field and the x axis. This relation which links the elec tron dynamics in the x-y real space and in the x-v parallel to phase s pace is verified by the numerical code. The Vlasov code provides a pow erful tool to study particle diffusion in space and in phase space, es pecially in the low-density regions of the distribution function.