Quasi-linear diffusion of magnetized fast electrons in momentum space results from stimulated emission and absorption of waves packets via wave-particle resonances. Such model consists in solving the dynamics of a system of classical kinetic diffusion processes described by the balance equations for electron probability density functions (electron pdf) coupled to the time dynamics waves (quasi-particles) in a quantum process of their resonant interaction. Such description results in a Mean Field model where diffusion coefficients are determined by the local spectral energy density of excited waves whose perturbations depend on flux averages of the electron pdf. We will discuss the model and a mean field iteration scheme that simulates the dynamics of the space average model, where the energy spectrum of the excited wave time dynamics is calculated with a coefficient that depends on the electron pdf flux at a previous time step; while the time dynamics of the quasilinear model for the electron pdf is calculated by the spectral average of the quasi-particle wave under a classical resonant condition where the plasma wave frequencies couples the spectral energy to the momentum variable of the electron pdf. Recent numerical simulations will be presented showing a strong hot tail an isotropy formation and stabilization for the iteration in a 3 dimensional cylindrical model. This is work in collaboration with Kun Huang, Michael Abdelmalik and Boris Breizman, all at UT Austin.[-]

Leveraging the existence of a hidden low-rank structure hinted by the diffusive limit, in this work, we design and test an angular space reduced order model for the linear radiative transfer equation based on reduced basis methods (RBMs). Our algorithm is built upon a high-fidelity solver employing the discrete ordinates method in the angular space, an upwind discontinuous Galerkin method for the physical space, with an efficient synthetic accelerated source iteration for the resulting linear system. Strategies are particularly proposed to tackle the challenges associated with the scattering operator within the RBM framework.
This is a joint work with Z.Peng, Y. Chen, and Y. Cheng.[-]

When designing high order schemes for solving time-dependent kinetic and related PDEs, we often first develop semi-discrete schemes paying attention only to spatial discretizations and leaving time $t$ continuous. It is then important to have a high order time discretization to main the stability properties of the semi-discrete schemes. In this talk we discuss two classes of high order time discretization, i.e, the strong stability preserving (SSP) time discretization, which preserves strong stability from a stable spatial discretization with Euler forward, and the explicit Runge-Kutta methods, for which strong stability can be proved in many cases for semi-negative linear semi-discrete schemes. Numerical examples will be given to demonstrate the performance of these schemes.[-]

A kinetic description of a plasma in external and self-consistent fields is given by the Vlasov equation for the particle distribution functions coupled to Maxwell's equation. Numerical schemes that preserve the structure of the kinetic equations can provide new insights into the long time behavior of fusion plasmas. In this talk, I
will present a structure-preserving particle-in-cell scheme for the Vlasov-Maxwell equations based on a finite difference description of the fields. Moreover, I will discuss the parallel implementation of this method based on the AMReX framework. This is joint work with Irene Garnelo and Eric Sonnendrücker.[-]