Numerical Studies of Plasma Stability and Alfvénic Modes with Energetic Particles in DTT
by
Bruno Brunelli
Frascati
V. Fusco, G. Vlad, S. Mastrostefano, M. Falessi, S. Briguglio, E. Giovannozzi, F. Zonca
Stability is a key requirement for safe and efficient operation of magnetic fusion devices: unstable plasmas can lose confinement, degrade performance, and in severe cases damage plasma-facing components. For this reason, a detailed stability assessment is being carried out for the Divertor Tokamak Test (DTT) [1], the new tokamak under construction in Frascati, designed to test divertor solutions capable of handling large thermal loads and power exhaust.
This work focuses on the full-power operating scenario [2]. High-resolution plasma equilibria are computed with CHEASE [3] and analyzed using the linear MHD stability code MARS [4]. The scenario is characterized by a central region with safety factor q < 1, which can destabilize ideal and resistive internal kink modes [5]. In addition, reactor-relevant high-performance conditions may excite so-called infernal modes, typically associated with low magnetic shear and steep pressure gradients at rational magnetic surfaces.
We also investigate global Alfvénic modes with the stability code MARS, as a preliminary step toward including energetic particles . Indeed, fast ions generated by auxiliary heating—such as radiofrequency waves or neutral beam injection—have velocities comparable to the Alfvén speed and can resonantly drive these modes unstable. This interaction may in turn degrade fast-ion confinement, limiting core heating efficiency and potentially increasing wall loads. In this study, energetic particles from a negative neutral beam injector are modeled using distribution functions from ASCOT [6-7] simulations and implemented as anisotropic slowing-down distributions within the hybrid MHD–gyrokinetic code HYMAGYC [8-9].
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[5] V.Fusco et al., EPS 2022, P2a.125.
[6] P.Vincenzi et al., Fus. Eng. Design 189 (2023) 113436
[7] C.De Piccoli et al., Front. Phys. 12 (2024) 1492095.
[8] G.Fogaccia et al., Nucl. Fus., 56:112004, 2016.
[9] G.Vlad et al., Rev. Mod. Plasma Phys. (2025).