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December 1997


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 experiment.
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 mode numbers.


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.


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.