Experimental validation for turbulence widening the plasma-wall-interaction area
The hot fusion plasma transfers a part of the generated heat to the plasma facing components. The size of the area of the interaction between the plasma and the wall is a critical parameter.
The hot fusion plasma will transfer the generated heat partially to the plasma facing components. The size of the area of the interaction between the plasma and the wall, measured by the so-called power fall-off length, is a critical quantity for a fusion reactor since it defines the temperature to which the wall material will heat up.
Widening of the power-wetted area with increasing turbulence control parameter. The color-coding represents the plasma collisionality. Notably the ASDEX Upgrade data span a range between zero and one, as predicted by theory.
A comparison of the power fall-off length of tokamaks worldwide showed that a linear increase with machine size but an inverse decreases with magnetic field strength, leading in sum to almost constant values.
Recent experimental studies on ASDEX Upgrade at the very edge close to the inner wall have now revealed that turbulence can widen this area by up to a factor of three. In the confined region, strong turbulence has a detrimental on the economy of a fusion reactor, at the very edge, however, it is beneficial since it increases the plasma-loaded area reduces the strain on the inner reactor components. The widening of the power-wetted area with the strength of the turbulence could be related to a theory-based parameter characterizing the turbulence strength (see figure). This work has recently appeared in Nuclear Fusion.