High Electron Temperature H-mode with N-NBI
On JT-60U, a clear H-mode transition with the electron temperature higher than the ion temperature was obtained by negative ion-based neutral beam injection (N-NBI : acceleration voltage = 340 keV). The ELMy H-mode was sustained for 1.3 seconds by N-NBI (Fig.1), and the N-NBI power was more than 70% of the total injected power.
The N-NBI dominantly heats the electrons in the central region. Due to this nature, the electron temperature was higher than that of the ions during the ELMy phase (Fig.2). The central electron temperature reached 1.4 times that of the ions. The L-mode enhancement factor of the energy confinement time (H factor) was 1.64 during the steady-state ELMy phase. In positive ion-based NBI H-modes, the electron temperature had never exceeded the ion temperature. An verification of H-mode transition by N-NBI electron heating has important contribution to the research of fusion plasmas in which the electron heating by α particles is dominant.
Fig.1 N-NB H-mode discharge
Fig.2 Electron and Ion temperature profiles