Speaker
Description
Linear (n=1) hybrid kinetic-MHD simulations have been performed with the NIMROD code to investigate energetic particle effects on (m=1,n=1) stability in SPARC plasmas. Understanding energetic particle-driven instabilities is critical for burning tokamaks, where fusion-born alphas can strongly modify the stability of MHD modes, impacting plasma confinement and performance. Using the SPARC Primary Reference Discharge
[ https://github.com/cfs-energy/SPARCPublic/tree/main/PrimaryReferenceDischarge ]
($B_0$=12T, I=8.7MA, $q_0$=0.93, $\beta_0$=4.5$\%$), a scan of energetic particle $\beta_\mathrm{hot}$ is carried out and growth rates and real frequencies are measured.
These simulations demonstrate that increasing $\beta_\mathrm{hot}$ stabilizes the ideal internal kink mode while simultaneously destabilizing an energetic particle-driven fishbone mode, illustrating the typical (1,1) transition from an MHD-dominated instability to a kinetic energetic particle mode [C. C. Kim, PoP 15 (2008)]. The NIMROD results are compared with corresponding linear calculations performed using the M3D-C1 hybrid kinetic-MHD model [C. Liu, CPC 275 (2022)], providing a cross-code benchmark of the growth rates and mode frequencies; additional validation of US flagship hybrid kinetic-MHD modeling tools for predicting energetic particle modes in next-generation fusion devices such as SPARC and ARC.
Phase-space diagnostics are presented to identify the dominant particle resonances that interact with the kink/fishbone mode. Both trapped and passing particles are shown to play a role in the evolution of the (1,1) mode. With these diagnostics, we highlight the localization and intrinsic connection of the resonant energetic particle orbits in both physical and velocity space. This multi-dimensional (5D) analysis provides an expanded view into the drift kinetic orbit topologies of energetic particles and theirs interaction with the (1,1) mode and creates some foundation for a bridge between the abstracted and idealized analysis of pencil-and-paper theory (e.g. zero width bananas) and the complications of real world experiments and their diagnostics.