Quantify energy transfer during wave-particle resonant interactions

Wave-particle resonances are foundational in plasma physics, with applications in essentially all subdisciplines. The resonance occurs in phase space but detailed, phase-space resolved measurements of the interaction are rare. This contribution presents the first-of-a-kind of these measurements in a tokamak, taken with the imaging neutral particle analyzer (INPA) [1], a detector which employes charge exchange reactions to determine the position and energy of the confined energetic particle (EP) population.



The DIII-D INPA systems were upgraded with a new set of fast channels, achieving temporal resolution of 1 MHz while maintaining a good resolution in phase space (7 keV in energy and 10 cm in radius). These new capabilities allowed to capture the fluctuations of the confined population of energetic particles both in the Alfvenic frequency range (~100kHz for typical DIII-D parameters) and the tearing mode (TM) frequency range (~15 kHz for typical DIII-D discharges). The relative fluctuation observed for the Alfvenic fluctuations is close to 15%. For the case of the TM frequency range, it ranges from 1 to 20%, depending on the mode amplitude.



The measured fluctuation of the confined EP, together with the electric fields extracted from the density and temperature fluctuations [2] allows for the characterization of the energy exchanged between the energetic particles and the waves [3]. This energy exchange will be compared to simulations performed by the hybrid-magnetohydrodynamic code MEGA, serving as an ideal validation case for its implementation for future machines.

[1] X. D. Du, et al., Nuclear Fusion 58, 082006 (2018).

[2] X. D. Du, et al., Phys. Rev. Lett. 132, 215101 (2024)

[3] Howes GG, et al., Journal of Plasma Physics. 83(1) 705830102 (2017)