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December 1995


The final installation of negative ion based neutral beams (N-NB) proceeds during this machine maintenance period. The analyses of the data for the last operation period are in progress and the experiment plan for the 1996 run is being discussed. In 1995, we have started exploring the plasma with high triangularity (up to 0.4) and achieved twice higher edge pressure during ELMy H-mode than that in the low triangularity plasma. The maximum plasma current in high triangularity discharge is, however, restricted to < 1 MA by the capacity of power supply for the controlling coil. To extend the plasma current in high triangularity discharge, the present PF power supplies are rearranged in December. High triangularity operation at higher plasma current (< 2 MA, triangularity < 0.3) will start in February 1996.


Main stream in 1996 will consist of 1) QDTeq push using 40 MW positive ion based neutral beams (P-NB) and 2) current drive and heating by the newly installed N-NB. Discussions on detailed approaches and planning are underway. In early 1996, high triangularity and shear reversal discharges can be operational up to 2 MA comparable to the current range of high-bp H-mode discharges. Using the ERATO-J code, the stability analysis for shear reversal discharges and high-bp discharge are ongoing. The operational frequency of ICRF waves is modified slightly downward so that the H-mode transition by ICRF heating alone becomes possible. Diagnostics rearrangements are being made in conjunction with the installation of N-NB. YAG laser Thomson scattering and motional Stark effect spectroscopy systems are upgraded to have 9 channels and 14 channels, respectively. The recent developments of JT-60U diagnostics were presented in ten papers including an invited paper at Toki conference in Toki.


Main subject of the steady-state study in 1996 is a demonstration of full current drive and heating using N-NB, especially to demonstrate a non-inductive current drive up to 2 MA with N-NB and P-NB. Extraction of 13.5 A D-beam at 400 keV for 0.2 s was already achieved with one ion source, which corresponds to 3 MW of N-NB power. The installation and the high voltage loading test of the second ion source are scheduled during this maintenance period. In 1996, both ion sources of N-NB will be conditioned for the operation with up to 10 MW of power and 4-5 s of pulse duration. In order to protect the first wall and the diagnostic port facing to N-NB from the heat load due to shine through, CFC tiles are used for the first wall and the armor of the port. The JT-60's divertor will be modified to W-shaped with pumping system in Nov. 1996 - Jan. 1997. The manufacturing of components for divertor modification (CFC and graphite tiles, base plates for the carbon tiles, etc.) are now in progress. Diagnostics systems (IRTV, Langmuir probe array, fiber optical array, spectrometers, bolometer array, millimeter-wave interferometer, etc.) will also be renewed/rearranged for the modified divertor geometry.