Description
The new eXtended Toroidal Accelerated PArticle Simulator (XTAPAS) is a recently developed hybrid simulation code conceived to describe the interaction between macroscopic magnetohydrodynamic (MHD) activity and energetic particles in magnetically confined plasmas. The model couples a reduced MHD solver [1] to a full-F, full-orbit kinetic module (the previously TAPAS code [1][3]) that follows the energetic particle trajectories without perturbative assumptions. This approach enables a self-consistent treatment of wave–particle resonances, finite orbit width effects, and nonlinear modification of the background plasma, while retaining the computational efficiency required for realistic device applications thanks to the GPU-acceleration.
The numerical implementation has been verified through a series of dedicated benchmarks. Simulations of toroidal Alfvén eigenmodes were compared with the reference results of the ITPA TAE benchmark case [4], showing very good agreement in mode frequency and growth rate. Further validation was performed against the NLED AUG benchmark [5], where XTAPAS reproduced the amplitude evolution, saturation levels and mode structure obtained with established codes, with special emphasis on the comparison with JOREK [6]. These studies confirm the capability of the scheme to capture both fluid and kinetic dynamics within a unified framework.
The code is now applied to the analysis of the JET discharge #99896 [7], characterized by strong destabilizing effect of energetic particle populations generated by NBI and ICRH with a rich Alfvénic activity. Initial simulations reproduce the dominant spectral features observed experimentally and indicate significant redistribution of fast ions associated with multiple mode interaction. The results demonstrate the potential of XTAPAS as a predictive tool for present devices and for the assessment of energetic particle stability in future burning plasma scenarios. Further work will address systematic validation against additional diagnostics and the extension to more comprehensive physics models.
[1] V. E. Lynch et al 1981 Comput. Phys. Commun. 24 465
[2] D. Zarzoso et al 2022 Plasma Phys. Control. Fusion 64 04400
[3] H. Betar et al 2024 Nucl. Fusion 64 126014
[4] A. Könies et al 2018 Nucl. Fusion 58 126027
[5] G. Vlad et al 2021 Nucl. Fusion 61 116026
[6] T. J. Bogaarts et al 2021 Phys. Plasmas 29 122501
[7] J. Garcia et al 2024 Nature Comm. 15 7846
*See the author list of “Overview of T and D-T results in JET with ITER-like wall” by CF Maggi et al. to be published in Nuclear Fusion Special Issue: Overview and Summary Papers from the 29th Fusion Energy Conference (London, UK, 16-21 October 2023)