14 / 2021-04-07 20:29:51

Self-consistent modelling of the electric field and minority distribution function for realistic RF heating and fast ion generation in W7-X

ICRH,Wendelstein 7-X,fast ions

Current stellarators have yet to demonstrate proper fast ion confinement, which is crucial for the design of a future reactor scale stellarator. In order to experimentally probe their confinement, these fast ions must first be generated at non-negligible densities. One way to do that is by heating with radio frequency (RF) waves. The SCENIC code is used to iteratively compute the RF electric field and the evolution of the minority distribution function until a self-consistent steady state solution is obtained [1,2,3]. The minority distribution function is sampled by markers that are followed along their full gyro-centred orbit, i.e. without bounce time averaging, in 3D stellarator equilibria. The so called `quasi-linear' approach is applied, where the RF electric field is computed using a linear model, but a minority distribution function is allowed to evolve non-linearly. One such non-linear effect is the fast ion temperature, which relies on the input power. This temperature moreover affects the distribution of collisional power to the background ions and electrons. This study investigates the fast ion generation and heating efficiency in W7-X for various RF schemes, which will be examined at different levels of coupled power.



[1] M. Jucker, \textit{Self-consistent ICRH distribution functions and equilibria in magnetically confined plasmas}, Ph.D. thesis, EPFL (2010)

[2] H. W. Patten et al., Phys. Rev. Lett. 124, 155001 (2020)

[3] M. Machielsen et al., subm. Plasma Phys. Controlled Fusion (2021)