M.Kuriyama, N.Akino, N.Ebisawa, L.Grisham*, M.Hanada, A.Honda, T.Itoh, M.Kawai, M.Kazawa, J.Koizumi, K.Mogaki, Y.Ohara, T.Ohga, K.Ohmori, Y.Okumura, H.Oohara, K.Ohshima, F.Satoh, H.Seki, T.Takenouchi, Tanai, Y.Toyokawa, K.Usui, K.Watanabe, H.Yamazaki and T.Yamazaki
JAPAN ATOMIC ENERGY RESEARCH INSTITUTE
Naka Fusion Research Establishment
Mukouyama, Naka-machi, Naka-gun, Ibaraki-ken, 311-01 Japan
*) PPPL
A high energy beam injection program for non-inductive current drive and plasma core heating in high density plasmas with the negative-ion based NBI system has been progressed since 1992 in JT-60U. An urgent task of the N-NBI program is to turn in a design data base for ITER plasma heating/ current drive device. The N-NBI aims at delivering a deuterium neutral beam of 500keV, 10MW for 10sec with one beamline using two negative ion sources. The NBI system was completed in the beginning of 1996, following which the beam injection into plasmas started in March 1996.
The first neutral beam injected into the JT-60U in March 1996 was 190keV,~0.1MW. After that, the beam injection into JT-60U has been continued with increasing the beam power. In September 1996, a beam power of 2.5MW at 350keV with deuterium had been injected for 0.9sec, and hence many effective data for NB current drive, plasma core heating and neutron yield in a plasma with high energy beam injections have been obtained. After some modification of the ion source and power supply in a maintenance period between November and December 1996, a neutral beam power of 3.2MW at 350keV had been injected for 1sec with hydrogen using one ion source. The negative ion currents and powers achieved, so far, with one ion source are 18.5A/H- at 350keV (6.5MW), and 13.5A/D- at 400keV(5.4MW), which are the highest negative ion current in the world with both hydrogen and deuterium beams. The neutralization efficiency of negative ion beams has been confirmed to be 60% as predicted theoretically for both H- and D- in a beam energy range of 250keV-380keV.
In a high energy beam injection up to 400keV into JT-60U plasmas, the characteristics of NBI current drive efficiency and neutron yield through plasma-beam/ plasma-plasma interactions, so far, have been confirmed to be consistent with predicted theoretically. The adaptability of negative-ion based NBI to tokamak device has also been proved positively through operating the N-NBI with no serious problem under the JT-60U tokamak environment. The beam power of the NBI is now being increased aiming at the rated power of 10MW at 500keV for a higher power NBI experiment in JT-60U.