January 1997
OPERATION PHYSICS
Three week operation was carried out in January using hydrogen and helium discharges to remove tritium absorbed in the first wall.
In a series of hydrogen discharges, q profiles was scanned by changing the Ip-ramp-up scenario to study effects of magnetic shear on formation of the internal transport barrier (ITB). Strong ITBs were established for the negative shear cases and very weak ITBs for nearly zero shear cases. The typical high beta-p mode characterized by the clear ITBs with positive shear was not obtained even at a low target density (<1e19m-3) because of limited heating power (<15MW) for hydrogen NB.
In ICRF heated reversed shear discharges, long sustainment of ITBs with a steep temperature gradient was demonstrated by ICRF4MW+NB1.5MW without minor collapses, which was likely related to a small density gradient across ITBs because of small central particle supply. In this case, the toroidal rotation shear is much weaker than that usually observed by NB heating.
CORE PHYSICS
Systematic study of neutral beam current drive (NBCD) was carried out using 80 keV beams. Controllability of current profile was demonstrated by changing the injection beam lines. It was confirmed that EFIT code (JT-60U/DIII-D collaboration) and MSE (motional Stark spectroscopy) measurements were very effective for reconstruction of the current density and toroidal electric field distribution to evaluate the beam driven current. Optimization of N-NB was progressed successfully for the heating and current drive studies planned in February.
Behavior of TAE modes was carefully studied by focusing on the effects of safety factor, density and rotation profiles: Frequency difference of bi-directional TAE modes observed in ICRF-heated low q plasmas was consistent with the Doppler-shifted difference of two modes separated from one mode excited in a gap of the Alfven continuum. Energetic proton confinement was significantly degraded when many TAE modes with different toroidal mode numbers occurred simultaneously inside q=1 surface. In ICRF-heated reversed shear plasmas with relatively weak density peaking, about 30 TAE modes appeared around q=2 surface.
BOUNDARY AND STEADY STATE OPERATION PHYSICS
Profiles of CII intensity in the divertor region at the initiation of the X-point MARFE started were measured with a 60-channel spectrometer(top view) and a 32-channel spectrometer(side view). The analysis of the two dimensional intensity distribution is under way. Dr. J. Terry from MIT participated in the divertor experiments for two weeks. He found that the volume recombination in divertor plasmas, which is significant in Alcator C-mod, was not so important in JT-60U.
LONG TERM VISITORS FOR JT-60U EXPERIMENTS
Dr. G.J.Kramer, STA Fellow, Netherlands, TAE and ELM research.
Dr. O.Da Costa, STA Fellow, France, IC emission research.
Dr. J.Cao, STA Scientist Exchange Program, SWIP, China, electron confinement research.
Dr. J.Koog, Post Doctoral Fellow, Korea, divertor research.
Dr. L. Yan, STA Scientist Exchange Program, SWIP, China, MHD research.
Dr. X. Gao, STA Scientist Exchange Program, ASIPP, China, transport research.
Dr. A. Polevoi, JAERI Research Fellow, Kurchatov Institute, Russia, transport research.
Dr. S. Neudatchin, ISTC Research Fellow, Kurchatov Institute, Russia, transport research.