Assessment of Methods to Infer Fluctuation Induced Transport with a Mirror Langmuir Mach Probe*

In principle, Langmuir probes can infer cross-field particle and energy transport arising from plasma turbulence. However, several challenges arise: (1) density, temperature and electric field must be measured or estimated at the same point in space; (2) electron temperature and floating potential fluctuations must be recorded to infer potential fluctuations; and (3) plasma interactions with the probe body (e.g. flows parallel and perpendicular to B) can affect local densities and potentials. A Mirror Langmuir Probe (MLP) bias technique can address challenges (1) and (2). Nevertheless, fluctuation-induced fluxes obtained by traditional analysis are found to exhibit significant scatter, which may be due to (3). Here we explore two new analysis techniques with the aim of mitigating the effects of (3). The first one attempts to correct for influence of plasma flows by applying a Mach probe analysis. The second one exploits the tendency for the plasma fluctuations to have a well-defined poloidal phase velocity in certain regions of the plasma, allowing transport to be deduced from a single MLP electrode. These two methods are compared against traditional techniques, taking advantage of the wealth of data collected on Alcator C-Mod.