A comparison of NIMROD's continuum and delta-f PIC approaches to energetic particle physics

Small number of energetic ions can have effect on long-wavelength modes in magnetized fusion [1]. PIC models have been used to model interaction in the context of initial value codes. The extended MHD code NIMROD has both continuum and delta-f PIC [2] drift kinetic (DK) capabilities that incorporate the energetic particle (EP), anisotropic stress tensor into its flow evolution equation. Two advantages of the continuum EP implementation are 1) the advance of the DK and flow evolution equations can be made fully implicit using Picard iterations within a single time step, and 2) a finite-element approach in pitch-angle resolves trapped/passing physics in velocity space. The continuum and delta-f methods are compared using model of giant sawtooth cycles in DIII-D shot \#96043. In this discharge, energetic ions are driven by RF and modifies the sawtooth stability. We present results from linear calculations that compare the accuracy and efficiency of the continuum and delta-f PIC methods using the slowing-down part of the EPs.

[1] W. Park, S. Parker, et al., Physics of Fluids B: Plasma Physics 4, 2033 (1992).

[2] C. C. Kim, C. R. Sovinec, et.al., Comp. Physics Communications 164, 448 (2004).