Energetic Particle Effects on Resistive MHD Instabilities with Varying Aspect Ratio

Advances in computational analysis have made it possible to simulate toroidal MHD equilibrium and stability, including physics outside of the MHD description, with a high degree of precision. Such simulations have recently begun to explore the interaction between non-Maxwellian particle distributions and resistive MHD stability. This project consists of an analysis of the interaction of a slowing down distribution of energetic particles with a m/n=2/1 resistive instability as a function of varying aspect ratio. Using the TOQ, PEST-III and NIMROD codes we initially characterize the MHD stability of the 2/1 mode without particles, and examine the particle effects with the NIMROD code. The equilibrium has a circular cross section and a Bessel function current derived from a linear perturbation in flux, allowing comparison to an analytic result at infinite aspect ratio. Methods and motivations for developing energetic particle effects into the PEST-III code are also discussed.