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May 1996


After one month regular maintenance, operation resumed from 28th May. The ICRF and LHRF aging was started for the IC heating and LHCD experiments. The injection power of 0.4 MW for ICRF and 2.3 MW for LHCD were achieved after 1 week aging. The properties of plasma position control have been investigated. The difference of ADCs bit error between for ZENKEI and PF coil power supplies was reduced by using common data. The voltage control was used instead of current control to reduce the fluctuation of PF-coil power supply voltage. As a results, the fluctuation of plasma radial position was suppressed by a factor of 8~10.


Current density profile analysis from the MSE measurement system upgraded to 14 channels is on going for the shear reversal discharges up to 2.1 MA in the April run for which an internal transport barrier was observed at a magnetic pitch minimum located around r~0.65a. Non-dimensional transport for ELMy H-mode plasmas with a triangularity of ~0.35 was analyzed in the high triangularity experiment in March where increase in triangularity lead to reducing the effects of ELM activity on local transport. Preliminary results from the two cases with Ip/Bt = 0.86 MA/1.86 T and 1.5 MA/3.08 T show that the thermal energy confinement time, tau-Eth, has the strong rho* dependence, which is almost like gyro-Bohm type scaling. The ion thermal diffusivity, chi-i, shows a gyro-Bohm like diffusion different from the Bohm like diffusion of chi-i previously obtained for L-mode plasmas in JT-60U. The high performance theme meeting was held. Major results from high triangularity, shear reversal and high-bp experiments conducted in this March and April run-period were assessed to showed remarkable progress in performance at high current regions. A summary paper entitled "ICRF Heating Results on JT-60U" was presented for the Meeting of the European Co-ordination Committee on Fast Wave Heating and Current Drive, held at Garching, May 21-22.


Five papers were presented from JT-60U team at the 12th International Conference on Plasma Surface Interactions in Controlled Fusion Devices (12th PSI conference), which was held in Saint-Raphael, France on May 20-25. A review talk was given by K. Shimizu entitled "A Review on Impurity Transport in Divertors". It summarized impurity transport codes (fluid codes and Monte Carlo codes) and impurity production in the divertors about JT-60U, JET, DIII-D, ASDEX-U and Alcator C-Mod. Modelling and process in each code were described to characterize particular features and simulation results. Carbon production at the private region between the hit points in high density plasmas can be explained by chemical sputtering due to low energy D0 in JT-60U and ASDEX-U. Based on the measured C IV profile, it has been found that carbon distribution in the divertor is well described by the balance between thermal force and friction force . A talk was given by S. Higashijima on carbon impurity generation by chemical sputtering. Profiles of CD-band intensities emitted from hydrocarbon molecules (mainly methane) were measured in the divertor region. The chemical sputtering yield of methane was estimated as a function of the surface temperature of divertor tiles and deuterium ion flux. The chemical sputtering yield is increased with the surface temperature and is decreased with an increment of the ion flux.