Validation of the 'full reconnection model' of the sawtooth instability in KSTAR

摘要

The central safety factor (q_0) during sawtooth oscillation has been measured with a great accuracy with the motional Stark effect (MSE) system on KSTAR and the measured value was ~ 1.0 ± 0.03. However, this measurement alone cannot validate the disputed full and partial reconnection models definitively due to non-trivial off-set error (-0.05). Supplemental experiment of the excited m = 2, m = 3 modes that are extremely sensitive to the background q_0 and core magnetic shear definitively validates the 'full reconnection model'. The radial position of the excited modes right after the crash and time evolution into the 1/1 kink mode before the crash in a sawtoothing plasma suggests that q_0 ≥ 1.0 in the MHD quiescent period after the crash and q_0 < 1.0 before the crash. Additional measurement of the long lived m = 3, m = 5 modes in a non-sawtoothing discharge (presumably q_0 ≥ 1.0) further validates the 'full reconnection model'.