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January 1996


The operation of JT-60U started in January as scheduled after the annual maintenance shut-down for about two and a half months. The vacuum vessel was closed on January 5 and vacuum pumping started on January 6. In the end of January, the coil excitation tests for the coming high triangularity operation up to 2 MA was successfully finished. The modification of the NBI system to narrow gaps of the acceleration electrode was completed for 40 MW injection with higher beam fueling at 90-95 keV. Drafts of about 60 papers for the JT-60U experimental review in 1995 were submitted and being circulated for publication in JAERI-Research Report.


Proposed shear reversal and high triangularity configurations for 2.0-2.5 MA operation were examined using equilibrium code simulations. Stability analysis of high triangularity plasmas for low-n kink/ballooning modes and transport analysis of shear reversal plasmas are ongoing. Triton burnup results are being analyzed on the basis of ripple transport theory. Calculation of ripple-induced fast ion losses proceeds using the orbit following Monte Carlo code. Two papers concerning shear reversal plasmas were presented in the US-Japan workshop held in Austin in USA, where the shear reversal plasmas were experimentally compared with high-bp mode plasmas and suppression of ion temperature gradient modes with negative magnetic shear was theoretically discussed.


High density limit, radiation power fraction in the divertor region and the degradation of the H-factor were investigated. Disruptive density limit and MARFE onset density in the divertor are increased with neutral beam injection up to PNBI = 8 MW. The density limit study will be continued in 1996 with higher PNBI approaching the Greenwald density limit. A new visible spectroscopic instrument with 32-channel optical fiber array was installed so that emission profiles of deuterium and low charge-states of carbon ions can be measured horizontally viewing the X-point and the strike point in the divertor zone. The spatial resolution of this instrument is about 12 mm at the X-point, and the profile data are sampled at typically 0.5 ms. Understanding the mechanisms of MARFE near the X-point and detached plasmas will proceed with this instrument in combination with the present measurement with 60ch-optical fiber array vertically viewing the divertor.