Finite ion temperature effects on scrape-off layer turbulence

Abstract

Ion temperature has been measured to be of the same order, or higher, than the electron temperature in the scrape-off layer (SOL) of tokamak machines, questioning its importance in determining the SOL turbulent dynamics. Here, we present a detailed analysis of finite ion temperature effects on the linear SOL instabilities, such as the resistive and inertial branches of drift waves and ballooning modes, and a discussion of the properties of the ion temperature gradient (ITG) instability in the SOL, identifying the g i ¼ L n =L T i threshold necessary to drive the mode unstable. The non-linear analysis of the SOL turbulent regimes by means of the gradient removal theory is performed, revealing that the ITG plays a negligible role in limited SOL discharges, since the ion temperature gradient is generally below the threshold for driving the mode unstable. It follows that the resistive ballooning mode is the prevailing turbulence regime for typical limited SOL parameters. The theoretical estimates are confirmed by non-linear flux-driven simulations of SOL plasma dynamics. [http://dx

Comparison of 3D flux-driven scrape-off layer turbulence simulations with gas-puff imaging of Alcator C-Mod inner-wall limited discharges

“…Finally, we stress that this initial validation exercise will be expanded, on one hand, by using a more advanced model including ion temperature dynamics and plasma shaping [20,31], and on the other hand, by comparing GBS against new experimental data from C-Mod's 2014 campaign. The new experimental series will include other advanced diagnostics, such as the mirror Langmuir probe and CXRS-GPI measurements of T i .…”

“…A model with constant ion temperature is used. Finite ion temperature effects are considered in [20], the principal result being that curvature driven modes (i.e. resistive ballooning modes) are slightly enhanced with respect to the cold ion model.…”

Blob properties in full-turbulence simulations of the TCV scrape-off layer

“…Also, finite ion temperature is considered important for blob dynamics [22] and may indeed play a role in the TCV SOL, where ions and electrons have similar temperatures. The equations determining the plasma dynamics are detailed in [21,23]. The boundary conditions at the limiter are described in [24].…”

Multi-code analysis of scrape-off layer filament dynamics in MAST

“…The GBS model changes in several ways with respect to the version used in [13]. First of all, the model was extended to allow for hot ion simulations, see [40] for the detailed equations (note however the change of normalisation, which in [40] uses the transit time instead of the inverse of the ion gyrofrequency). In the work presented here, both cold and hot ion simulations were performed with GBS.…”