High ion temperatures and transport characteristics of high Z_eff hydrogen plasmas in JT-60 limiter discharges

Ion temperatures around 10 keV were obtained in JT-60 limiter plasmas by high power neutral beam heating (H⁰ → H⁺), which is much higher than the maximum value of 6.6 keV obtained in JT-60 diverted plasmas. The experiment was performed in the parameter region of I_p = 1−2 MA, _e (before heating) = (0.7−1.5)×10¹⁹ m⁻³_e (end of heating) = (2.5−4.1)×10¹⁹ m⁻³ and = 19−21.8 MW. The Z_eff values of the limiter plasmas were high (i.e. 4 to 7) compared with those of the diverted plasmas (i.e. 1 to 2). Transport analysis indicates that, since the deposition power to electrons, P_beincreases with Z_effhigh Z_eff is effective in raising the electron temperature. Furthermore, it is shown that since the equipartition loss is reduced by both the increase in electron temperature and the decrease in the effective ion density, n_p + n_zZ²m_pm_zwith increasing Z_effhigh ion temperatures are obtained in limiter plasmas with high Z_eff.