Validation of OSHUN against collisionless and collisional plasma physics

OSHUN, a Vlasov-Fokker-Planck-Maxwell code, is successfully validated against a few collisionless and collisional plasma physics test problems. In OSHUN, the distribution function is expanded in velocity (or momentum) space into an arbitrary number of spherical harmonics. OSHUN is shown to accurately recover Landau damping by including a relatively small number of spherical harmonics for an initial value problem as well as a driven plasma wave. The Fokker-Planck operator (both electron-electron and electron-ion) is shown to be able to reproduce the Epperlein-Haines heat-flow coefficient in warm, un-magnetized and magnetized plasmas with varying degrees of ionization. These collisionless and collisional problems are of disparate time- and length- scales ranging from femtoseconds to nanoseconds, and from microns to millimeters. OSHUN's ability to handle these test problems successfully illustrates the power of the spherical-harmonic expansion when studying both weakly-collisional and collisional plasmas relevant to high-energy-density physics. The implementation and use of new features such as a ponderomotive wave driver and an implicit collision operator is also discussed.