Description
Tokamak equilibrium shaping can significantly influence the frequencies of trapped particle Guiding Center (GC) orbits, thereby modifying the resonance structure with external perturbations [1,2], which plays a crucial role in particle, energy and momentum transport. In shaped equilibria, the bounce frequency profile may become non monotonic with respect to the particle energy, enabling additional resonance locations in phase space and more complex perturbed dynamics.
In this work we investigate the effect of plasma shaping on GC orbit frequencies by computing Orbital Spectrum (OS) and resonance diagrams in the constants of motion space, which reveal how these modifications extend across the GC phase space. This behaviour can be particularly pronounced at small aspect ratio and negative triangularity equilibria, where secondary families of trapped orbits may emerge, due to bifurcations of the GC critical points.
We compare resonance maps and Poincare sections for positive and negative triangularity equilibria in various machines, including SMART and DTT, highlighting the effect of plasma shaping on resonances with n = 0 perturbations and particle‑orbit chaoticity. These results extend our previous work on OS modifications driven by radial electric fields [3], demonstrating that plasma shaping can likewise tailor GC dynamics and provide an additional design handle for transport-barrier formation in fusion reactors.
References
[1] J. P. Graves. Plasma Phys. Control. Fusion 55 074009 (2013)
[2] Guangyu Wei et al., Nucl. Fusion 65 106035 (2025)
[3] G. Anastassiou, P. Zestanakis, Y. Antonenas, E. Viezzer and Y. Kominis, J. Plasma Phys. 90, 905900110 (2024)