Scenario development toward high beta steady-state operation at KSTAR

Solving issues for high-beta long-pulse operation is one of the essential topics for superconducting tokamaks and sustainment of a fully non-inductive H-mode discharge with high performance is successfully demonstrated upto record-long \textasciitilde 70 seconds at KSTAR. Typical plasma parameters are 0.4MA(I$_{\mathrm{p}})$, max 5MW (NBI$+$ECH), $\beta _{\mathrm{p}}$\textasciitilde 3, f$_{\mathrm{BS}}$\textasciitilde 0.5, H$_{\mathrm{98}}$\textasciitilde 1.3 and in a wide range of q$_{\mathrm{95}}=$6\textasciitilde 12. Though an internal transport barrier is not identified yet, the developed scenario has many features in common with the so called “high $\beta_{\mathrm{p}}$ discharge” at DIII-D. The thermal confinement is sensitive on the deposition layer of the central ECH heating \textasciitilde 1MW and it correlates with MHD activities in the range of TAE frequency (100\textasciitilde 200kHz) suggesting strong interaction TAE with fast ion transport. Based on the transport/stability analysis on the present discharge, improved performance is also estimated with higher NBI$+$ECH heating power envisaged in near future.