Data-Driven Representations of Ion-Kinetic Distribution Functions

Collisionless processes, such as wave particle interactions, are key to understanding the energy transfer in plasma environments. While collisional interactions are known to result in a distribution of particle velocities close to a thermal Maxwell-Boltzmann distribution, wave-particle interactions produce distribution functions that may diverge significantly from thermal equilibrium. Correct measurement and representation of non-thermal features is key to understanding the collisionless wave-particle interactions and how they shape plasma distributions. Here, we present and expand on methods (Polynomial interpolation, radial basis functions) used to approximate ion distribution functions observed by Parker Solar Probe. These non-parametric representations of the observed distributions can be used to understand instability growth rates and resonant heating of the solar wind plasma.