Recent experimental and analytic progress in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade with W-shaped divertor configuration

The Japan Atomic Energy Research Institute (JAERI) completed the divertor modification of the JAERI Tokamak-60 Upgrade (JT-60U) [Y. Koide and the JT-60 Team, Phys. Plasmas 4, 1623 (1997)] in June, 1997, and experiments with the W-shaped pumped divertor have been carried out. The helium exhaust was demonstrated in the steady state by using helium neutral beam injection (NBI). The ratio of the effective particle confinement time of helium to the energy confinement time, ${\tau }_{\mathrm{He}}^{*}{\mathrm{/\tau }}_E,$ became about 4 and the obtained enrichment factor of helium in the divertor was about 1. The high confinement mode (H-mode) plasma with edge localized mode (ELM) was sustained for 9 s with a confinement–enhancement factor (H factor) of $\text{∼1.7.}$ No increase of recycling and carbon impurity density was observed with the integrated NBI input energy of 203 MJ. In the reversed shear (RS) experiments, a quasi-steady-state $\mathrm{ELM}y$ H mode was achieved with an H factor $\text{∼2.4.}$ The stability of high-$n$ toroidal drift modes was analyzed in the RS plasma. The $\mathrm{E\times B}$ shearing rate became of the same order of magnitude as the linear growth of the dominant mode around the internal transport barrier. The semiglobal structure of radial transport was analyzed by the toroidal geometry particle simulation code. The discontinuity in the electrostatic potential occurred at the $q_{\min }$ region and radial transport was reduced.