OSHUN is a unique parallel relativistic 2D3P Vlasov-Fokker-Planck (C++) code that incorporates a spherical harmonic expansion of the distribution function, where the number of terms is an input parameter that determines the angular resolution in momentum-space. The algorithm employs the full 3D electromagnetic fields and a rigorous linearized Fokker-Planck collision operator. The numerical scheme conserves energy and number density. The main advantage of this approach is realized for collisional plasmas, in which angular scattering tends to isotropize the distribution function by rapidly damping the high-order harmonics. This makes it is possible to capture most of the key physics using only a few terms in the expansion.
Below we present three tests with the code:
- The evolution of the relativistic two-stream instability in the frame of reference of the unstable wave.
- The relaxation of a bump-on-tail particle distribution to a Maxwellian due to electron-electron collisions.
- The calculation of the Spitzer-Harm heat conduction coefficient.
Figure 1: The evolution of the relativistic two-stream instability in the frame of the unstable wave is shown from a simulation with OSHUN.
Figure 2: The evolution of a bump-on-tail distribution of electrons under the influence of collisions between identical particles.
The code recovers the Spitzer- Härm heat conduction with excellent accuracy.