The Kinetic Analog of the Pressure-Strain Interaction*

Energy conversion in weakly collisional plasma systems is often studied with fluid models and diagnostics. However, the applicability of fluid models is necessarily limited when collisions are weak or absent, and using a fluid approach can obscure kinetic processes that provide key insights into the physics of energy conversion. A kinetic technique that retains all of the information in 3D-3V phase-space for the study of energy transfer between electromagnetic fields and kinetic energy (quantified by the rate of electromagnetic work in fluid models) is the field-particle correlation technique (Klein et al. JPP, 2017). This technique has demonstrated that leveraging the full information contained in phase-space via kinetic diagnostics can elucidate the mechanisms of collisionless energy transfer. A different channel of energy conversion—between fluid flow energy and particle internal energy— is quantified in fluid models via the pressure-strain interaction (Yang et al. PoP, 2017). Using a similar approach to that of the field-particle correlation technique, in this work we derive a kinetic analog to the pressure-strain interaction and use it alongside the field-particle correlation to analyze the flow of energy from electromagnetc fields into particle internal energy in two case studies of electron Landau damping.