Researchers have benchmarked a new gyrokinetic simulation code, named TEK, against a standard test case established by the International Tokamak Physics Activity (ITPA) Energetic Particle (EP) topical group. The benchmark focuses on the simulation of toroidal Alfvén eigenmodes (TAEs) driven by energetic particles, a critical phenomenon for predicting alpha particle behavior in burning plasmas. The results, detailed in a preprint posted to arXiv, demonstrate TEK's capabilities in both linear and, notably, nonlinear regimes. While linear benchmarks for this case are well-established across multiple codes, this work provides new, much-needed data for nonlinear inter-code comparisons, addressing a gap in the verification of complex plasma simulation tools. Source: arXiv

The TEK code treats all plasma species—electrons, thermal ions, and energetic particles—on equal footing within the gyrokinetic model, with electrons handled in the zero Larmor radius limit. This unified approach is designed to capture the intricate wave-particle interactions that govern the stability of fusion plasmas. To manage the numerical challenge known as the electromagnetic cancellation problem, which can degrade accuracy in high-beta simulations, TEK implements a mixed-variable pullback method. The paper discusses these numerical details, offering insights for developers of similar electromagnetic gyrokinetic codes aiming to model the complex dynamics of energetic particles. Source: arXiv

This unified approach is designed to capture the intricate wave-particle interactions that govern the stability of fusion plasmas.

A key contribution of this research is its extension into the nonlinear saturation phase of TAEs. The study presents results for both single toroidal mode number (n) and multiple-n simulations. The authors report that the nonlinear outcomes align well with an analytical theory describing zonal field generation through the beating of Alfvén eigenmodes. This agreement provides partial verification of the code's nonlinear physics implementation. The analysis examined the saturation level of the modes and the consequent transport of energetic particles, which are primary outputs for assessing the potential impact of such instabilities on plasma confinement and performance. Source: arXiv

The ITPA benchmark case provides a simplified tokamak configuration, allowing for direct comparison between different simulation codes without the complexities of specific experimental geometries. By successfully completing both linear and nonlinear phases of this benchmark, TEK establishes its credibility as a tool for investigating EP physics. The data generated, particularly on nonlinear saturation and EP transport, is intended to serve as a reference for future benchmarking efforts by the international fusion modeling community. This work contributes to the foundational validation required before such codes can be confidently applied to predictive modeling for devices like ITER and future fusion power plants. Source: arXiv