Abstract
Understanding the dependence of the H-mode power threshold, on the main ion composition is crucial for H-mode operation in ITER. In this work, H-mode power threshold studies conducted at ASDEX Upgrade are presented. These were performed in hydrogen plasmas with helium doping and in mixed hydrogen-deuterium plasmas. stays constant on the level of pure hydrogen in hydrogen plasmas with helium doping up to . Power balance calculations with the transport code ASTRA show that the edge ion heat flux at the L-H transition is independent of helium concentration and applied auxiliary heating, supporting that a critical edge ion heat flux is needed to enter H-mode. A non-linear dependence of on the relative hydrogen content is found. and the edge ion heat flux are constant at the level of pure deuterium for between 0 and 0.5 and constant on the level of pure hydrogen for between 0.8 and 1.
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