Changes in the Toroidal Velocity Profile During Disruptions on KSTAR

A real-time toroidal velocity (rtVphi) system has been installed on KSTAR as part of the real-time diagnostic suite for the Disruption Event Characterization and Forecasting (DECAF) research program [1]. This paper presents the overall specifications and integration scheme of the rtVphi system. The new 32-channel diagnostic currently operates with a data acquisition rate of 0.4 kHz. Using data from disruptive discharges in the 2024 campaign, changes in the toroidal velocity profile have been analyzed. In particular, discharges that end in disruptions triggered by repetitive sawtooth crashes exhibit a reduction in toroidal velocity in the core channels, along with a decrease in ion temperature shortly before disruption. At the onset of disruption, several core channels (R < 1.9 m) display signatures consistent with counter-streaming ion beams, suggesting a three-dimensional nature to the disruption dynamics. Further analysis incorporating ECE and ECEI data is planned to better understand these observations.

[1] S.A. Sabbagh, et al. Phys. Plasmas 30, 032506 (2023)