Turbulence Spreading and Transport Properties in the Core and Boundary Layer of the C-2W Field-Reversed Configuration

In the C-2W Field Reversed Configuration (FRC), a closed-fieldline FRC plasma is embedded in an (open fieldline) mirror plasma. We investigate here the interaction of the mirror plasma scrape-off layer, characterized by drift-interchange turbulence with an exponential toroidal wavenumber spectrum, and the much more quiescent FRC core, characterized by very low ion-scale turbulence levels, and a flat or inverted toroidal wavenumber spectrum [1]. Gyrokinetic simulations of the coupled mirror/FRC plasma have predicted turbulence spreading from the (unstable) SOL into the (stable) FRC core [2]. Doppler Backscattering measurements show that radial turbulence correlation properties change significantly near the excluded flux radius. We compare here correlation properties and investigate the radial structure of ion- and electron-scale turbulence and E×B flows, to uncover evidence for the predicted Zonal Flows and spectrally dependent radial turbulence spreading.   We also investigate the role of E×B flow shear (controllable within certain limits with electrostatic biasing of the SOL plasma via annular divertor electrodes) for turbulence spreading and radial transport across the FRC excluded flux radius.

[1] L. Schmitz et al., Nature Comm. 7 13860 (2016).                                                                   

[2] C. Lau et al., Nucl. Fusion 59 066018 (2019).