JT-60U MONTHLY SUMMARY
OPERATION AND CONFINEMENT PHYSICS
As the JT-60U January campaign is anticipated to start in high-elongation
configurations, which has not been performed after the modification of the
divertor geometry in 1997, numerical equilibrium database was produced to
evaluate the plasma control parameters based on the function parametrization
method. The total number of data accumulated was extended to 815 to accommodate
the broad ranges of operational parameters expected in the 1998 high-performance
According to analyses of the fusion gain QDT for the long pulse high performance
discharges, QDT~0.1 was sustained for 9 sec in the low triangularity (defined
at the outermost closed flux surface = 0.16) discharge and QDT~0.16 for
4.5 sec in the high triangularity (0.3) discharge at plasma current Ip=1.5MA.
The key phenomenon limiting QDT was the resistive instabilities with low
CURRENT DRIVE AND HIGH ENERGY PARTICLE PHYSICS
Experiment proposals on current drive and energetic particle physics studies
were discussed for the operation from January to March, 1998. The current
drive and TAE mode experiments using NNB are scheduled in February and March,
1998. Regarding the NNB current drive, improvement of current drive efficiency
in a high electron temperature regime and demonstration of non-inductive
fully current drive at Ip =1.5 MA are main objectives. In the TAE mode studies,
the mode excitation will be explored at the higher toroidal magnetic field
than 1.5 T and impacts on beam ion confinement and current drive efficiency
will be investigated.
Ion sources and power suppliers of NNB were improved in November and December,
1997, for stable operation at high energy and high power.
DIVERTOR AND BOUNDARY PHYSICS
The maintenance of diagnostic systems were carried out during the vacuum
vent period. Divertor bolometers, ASDEX gauges and Penning gauges which
were damaged or did not work during June-October experiment were repaired.
Langmuir probe tips plugged into divertor tiles suffering from erosion were
exchanged to new ones. The position of X-point Langmuir probe was extended
to be able to measure plasmas in the X-point vicinity. IRTV system was rearranged
to observe the divertor and dome tiles.
H. Kubo presented recent results of spectroscopic study on attached and
detached divertor plasmas in JT-60U in the scientific meeting on "Spectroscopic
studies on non-equilibrium plasmas" held in Kyoto on Dec. 11. From
measurement of the Balmer series lines and the Balmer and Paschen continuum
of deuterium, the electron temperature at the outer divertor in a partially
detached plasma was estimated to be higher than 10 eV, showing that the
recombination process was not dominant. This result is different from those
in ALCATOR C-Mod etc., where the recombination plays an important role in
the detached divertor. Further study is necessary with a spatially resolved
observation and a high-resolution spectrometer to understand the difference.
N. Hosogane attended the First Japan-China Workshop on Improved Performance
in Toroidal Plasmas held in P. R. China on Dec. 11-14. He presented recent
experimental results on the JT-60U W-shaped divertor entitled "Performance
of Semi-closed W-shaped Divertor in JT-60U". He discussed Japan-China
collaboration in tokamak experiments with Chinese scientists.