From Power Exhaust to Dilution & Radiation Collapses: Impurity transport and radiation physics in W7-X

Power dissipation in the boundary plasma with radiation from actively seeded impurities will be mandatory for future fusion devices. Hence, the presence of impurities in the plasma is not only unavoidable, but also desired in the boundary plasma domain. At the same time, the contamination of the confined plasma with impurities comes at the cost of plasma performance and even the limitation of the accessible operational parameters due to the occurrence of radiation collapses. This contradicting requirements on the impurity content in different parts of a reactor fusion plasma necessitates a detailed investigation of impurity transport and of the processes that stipulate radiation losses. A detailed understanding will allow us to determine and to control an optimized operation scenario in a future reactor. The talk introduces the current state of understanding of impurity transport in the boundary and the confined plasma as well as the observations on the radiative losses and its role in power exhaust in W7-X.