München 2019 – wissenschaftliches Programm
P 18.50: Poster
Donnerstag, 21. März 2019, 16:30–18:30, Foyer Audimax
Impurity injection beyond the tracer-limit by means of laser blow-off in W7-X. — •Th. Wegner and The W7-X Team — Max-Planck-Institute for Plasma Physics, Greifswald, Germany
The investigation of impurity transport properties is a demanding task for fusion devices with the potential of steady-state operation since central accumulation of those highly charged ions could yield too strong radiative cooling. One prominent method to study the impurity confinement is based on the injection of impurity ions via the laser blow-off technique. Basically, the impurity transport analysis relies on an impurity injection within the tracer- limit to exclude collisions between impurities and their influence on the background plasma. Hence, each ionization stage can be treated separately and the coupling to neighboring states is only determined by ionization and recombination. To estimate the trace approximation limit and to study the disturbing impact of massively impurity injection on the plasma parameters, the amount of particles injected by means of laser blow-off was increased during an experimental program. Thus, the ablation spot size as well as the laser energy density on the coated target were changed. As a result, the injected impurity amount was increased until the perturbation by the injection itself led to radiative collapse and hence to an early pulse termination. Additionally, the composition of the particle beam changed with respect to the amount of clusters and macro particles as a consequence of the reduced laser energy density.