JT-60U MONTHLY SUMMARY
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.
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
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
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
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
Dr. S. Neudatchin, ISTC Research Fellow, Kurchatov Institute, Russia, transport