Enhanced ion heating in a field-reversed configuration fusion device via beam-driven waves

Beam-driven field-reversed configuration (FRC) plasmas are a promising concept in magnetic confinement fusion research [1]. Experiments in the C-2W device have explored various operational regimes, some of which achieve high-beta FRC plasma sustainment at lower densities and greater ratio of fast-ion pressure relative to thermal plasma pressure. Spectroscopic diagnostics, both passive and active, reveal enhanced ion heating and elevated thermal ion temperatures in these regimes, reaching values greater than 1 keV for the bulk ions and 5 keV for impurity ions. Experimental observations indicate a strong correlation between bulk and impurity ion energy distributions and high-frequency magnetic fluctuations, particularly at harmonics of the ion cyclotron frequency. These results suggest that energy transfer from fast ions to thermal ions via beam-driven waves is enhanced in these low collisionality regimes. This work details the experimental techniques and data analysis methodologies used to extract physical parameters of the plasma from spectroscopic and magnetic measurements, and provides an in-depth discussion of the experimental observations.

[1] H. Gota, et al., Nuclear Fusion 61, 106039 (2021)