Study of Plasma Current Decay in the Initial Phase of High Poloidal Beta Disruptions in JT-60U

In order to validate some current decay models during the current quench, the plasma current decay time was studied using the experimental plasma resistance and inductance in high poloidal beta, βp, disruptions in JT-60U. The plasma resistance and inductance were evaluated from an equilibrium calculation code and the measurement value of a magnetic sensor, the electron temperature evaluated by using ECE measurement and the electron density measured by FIR interferometer. In high βp disruptions, it was found that the electron temperature at the plasma center just after current quench starts was approximately 1-4 keV under almost the same current decay time observed during the initial phase of current quench. This result indicates that the electron temperature itself plays no major role in the determination of the current decay time in the initial phase of current quench. Moreover, the current decay time predicted by a modified L/R model [Y. Shibata et al., Nucl. Fusion 50, 025015 (2010)], in which the time derivative of plasma inductance was considered, was in good agreement with the experimental current decay time, while the values obtained from the conventional L/R model were two orders of magnitude larger than the experimental results.