Parametric dependences of the heat flux footprint on the outer divertor target plate are explored in EDA H-mode and ohmic L-mode plasmas over a wide range of parameters with attached plasma conditions. Heat flux profile shapes are found to be independent of toroidal field strength, independent of power flow along magnetic field lines and insensitive to x-point topology (single-null versus double-null). The magnitudes and widths closely follow that of the "upstream" pressure profile, which are correlated to plasma thermal energy content and plasma current. Heat flux decay lengths near the strike-point in H-and L-mode plasmas scale approximately with the inverse of plasma current, with a diminished dependence at high collisionality in L-mode. Consistent with previous studies, pressure gradients in the boundary scale with plasma current squared, holding the magnetohydrodynamic ballooning parameter approximately invariant at fixed collisionality-strong evidence that critical-gradient transport physics plays a key role in setting the power exhaust channel.

The mitigation of divertor heat fluxes is an active topic of investigation on existing tokamaks.One approach uses radiation, both inside and outside the last closed flux surface (LCFS), to convert plasma thermal energy, usually directed towards dedicated plasma facing components, to soft x-ray and ultraviolet radiation, spread over a much larger surface area. Recent enhanced D- H-mode experiments on Alcator C-Mod varied the ICRF input power and radiative power losses via impurity seeding to demonstrate that normalized energy confinement depends strongly on the difference between input power and the radiated power inside the LCFS. These investigations also show that when seeded with either Ne or N 2 , a factor of two and higher reduction in outer divertor heat flux is achieved while maintaining H 98,y2 ~ 1.0. Conversely, when seeding with Ar, confinement is limited to H 98,y2 ~ 0.8 for a similar level of exhaust power.

Alcator C-Mod is a particularly challenging environment for thermography, presenting issues that will similarly face ITER, including: low-emissivity metal targets, low-Z surface films, and closed divertor geometry. In order to make measurements of the incident divertor heat-flux using IR thermography, the CMod divertor has been modified and instrumented. A 6 o toroidal sector has been given a 2 o toroidal ramp in order to eliminate magnetic field-line shadowing by imperfectly aligned divertor tiles. This sector is viewed from above by a toroidally displaced IR camera and is instrumented with thermocouples and calorimeters. The camera provides time-histories of surface temperatures that are used to compute incident heat-flux profiles. The camera sensitivity is calibrated in-situ using the embedded thermocouples, thus correcting for changes and non-uniformities in surface emissivity due to surface coatings.