Non-inductive improved H-mode operation at ASDEX Upgrade

Recent improvements to the heating and diagnostic systems on the ASDEX Upgrade tokamak allow renewed investigations into non-inductive operation scenarios with improved confinement in a full-metal device. Motivated by this, a scenario with ${\beta }_N\approx 2.7$, $q_{95}\approx 5.3$ and a high non-inductive current fraction $f_{NI}\gtrsim 90\%$ has been developed. The scenario offers good confinement with $H_{98}(y,2)>1.1$ and normalised ion temperature gradients $R/L_{T_i}\approx 12$. Moreover, it is robust against resistive magnetohydrodynamic (MHD) instabilities, but does suffer from ideal MHD instability when ${\beta }_N\gtrsim 2.8$. To verify the understanding of the plasma transport processes, the heat transport was modelled using TGLF. This revealed that electromagnetic effects at high β and/or from fast ions appear to be missing from TGLF's physics model. As accurate reconstruction of the plasma equilibrium is crucial for studies of advanced scenarios, this publication also documents the presence of polarised background light that can contaminate motional stark effect measurements and thus interfere with equilibrium reconstruction. (paper)