Energetic particles, Shafranov shift and finite β effects on TAE, KBM and ITG instabilities in global electromagnetic gyrokinetic simulations
Abstract
Burning plasma is computationally challenging to simulate due to the multi-scale interactions between energetic particles (EPs), Alfven eigenmodes, and microinstabilities that drive turbulence. Many studies circumvent this difficulty by focusing on a single instability and making the corresponding simplifying assumptions. However, these approximations do not necessarily preserve the global instability spectrum, leading to conflicting results and inconsistencies. In this work, we identify the minimal set of assumptions needed to model a burning plasma self-consistently with the modes and species in the system. Using the global gyrokinetic code ORB5, to systematically evaluate the impact of commonly adopted assumptions on the plasma response. We find it is essential to include Shafranov shift and finite β effects from all magnetically confined species. Otherwise, unphysical electromagnetic modes like internal kinks and kinetic ballooning modes (KBMs) appear to dominate the instability spectrum. The EP contribution to the Shafranov shift is particularly important, stabilizing both the toroidal ion temperature gradient (ITG) and toroidal Alfven eigenmode (TAE) at the longer wavelengths (low toroidal mode numbers). For TAEs, these effects significantly reduce the linear growth rate, which saturates instead of proportionally increasing with EP fraction. In the nonlinear regime ITG-driven heat and particle fluxes are unaffected by the Shafranov shift in self-consistent magnetic equilibria. While the the nonlinear saturation level of the TAE remains unchanged across all cases, unlike for the ITG case Shafranov shift does reduce the TAE-driven EP fluxes.
Related
- Global Gyrokinetic Simulations of Electromagnetic Turbulence in STEP
- The new Toroidal Accelerated PArticle Simulator (TAPAS) for the study of energetic particle instabilities in fusion plasmas
- ORB5X: a performance-portable global electromagnetic gyrokinetic PIC code in C++/Kokkos built using Agentic AI
- Design of the IMAS interface data structure for flux-tube gyrokinetic simulations
- Mitigation of Initial Transients in Total-f Gyrokinetic Turbulence Simulations Using Neoclassically Relaxed Distribution Function
BibTeX
@misc{rofman2026energetic,
title = {{Energetic particles, Shafranov shift and finite $β$ effects on TAE, KBM and ITG instabilities in global electromagnetic gyrokinetic simulations}},
author = {B. Rofman and G. Di Giannatale and A. Mishchenko and E. Lanti and A. Bottino and T. Hayward-Schneider and J. N. Sama and A. Biancalani and B. F. McMillan and S. Brunner and L. Villard},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.17138},
eprint = {2605.17138},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.17138},
}
RIS
TY - UNPB
TI - Energetic particles, Shafranov shift and finite β effects on TAE, KBM and ITG instabilities in global electromagnetic gyrokinetic simulations
AU - B. Rofman
AU - G. Di Giannatale
AU - A. Mishchenko
AU - E. Lanti
AU - A. Bottino
AU - T. Hayward-Schneider
AU - J. N. Sama
AU - A. Biancalani
AU - B. F. McMillan
AU - S. Brunner
AU - L. Villard
PY - 2026
DA - 2026/09/04
PB - arXiv
DO - 10.48550/arxiv.2605.17138
UR - https://arxiv.org/abs/2605.17138
AB - Burning plasma is computationally challenging to simulate due to the multi-scale interactions between energetic particles (EPs), Alfven eigenmodes, and microinstabilities that drive turbulence. Many studies circumvent this difficulty by focusing on a single instability and making the corresponding simplifying assumptions. However, these approximations do not necessarily preserve the global instability spectrum, leading to conflicting results and inconsistencies. In this work, we identify the minimal set of assumptions needed to model a burning plasma self-consistently with the modes and species in the system. Using the global gyrokinetic code ORB5, to systematically evaluate the impact of commonly adopted assumptions on the plasma response. We find it is essential to include Shafranov shift and finite β effects from all magnetically confined species. Otherwise, unphysical electromagnetic modes like internal kinks and kinetic ballooning modes (KBMs) appear to dominate the instability spectrum. The EP contribution to the Shafranov shift is particularly important, stabilizing both the toroidal ion temperature gradient (ITG) and toroidal Alfven eigenmode (TAE) at the longer wavelengths (low toroidal mode numbers). For TAEs, these effects significantly reduce the linear growth rate, which saturates instead of proportionally increasing with EP fraction. In the nonlinear regime ITG-driven heat and particle fluxes are unaffected by the Shafranov shift in self-consistent magnetic equilibria. While the the nonlinear saturation level of the TAE remains unchanged across all cases, unlike for the ITG case Shafranov shift does reduce the TAE-driven EP fluxes.
ER -