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November 1996


Development of vertical position (Zj) control has been continued to avoid VDE during Ip-quench phase. By this time, the operation regime was extended toward a ITER-like low-q regime. The coefficients of the statistical method were re-modified by both steady state and Ip-quench databases, adding the data of previous Zj control discharges to improve the accuracy of real-time calculation of Zj during Ip-quench. After the modification, the Zj was successfully controlled and VDE was avoided during Ip-quench at q95~2.9 (Ip=1.7 MA, density limit disruption).


TAE experiments were carried out in helium discharges with hydrogen minority ICRF heating. Magnetic fluctuation measurements for TAE were made with a fast sampling rate of 1 MHz. The toroidal mode numbers from n=13 down to 4 were observed at IP=2.6 MA and BT=3.48 T. Simultaneously, the counter-rotating TAE mode with n=4 and 5 for the first time. The mechanism of the bi-directional TAE modes generation is being investigated.

Detailed analyses for the high performance discharge equivalent to the break-even condition achieved in October 1996 were in progress. Evaluation of the effects of toroidal field ripple on beam ion losses is ongoing.

The joint workshop of JT-60U and JFT-2M on H-mode physics (ELMs, edge pedestal, L-H and H-L transitions) and divertor physics (radiative divertor, cold&dense divertor, SOL, He exhaust, particle confinement, edge neutrals) was held during 26-27 Nov., in which 21 papers were presented with vigorous discussions from about 40 attendees.


In order to study the reason why the density limit in helium OH discharges is higher than those in hydrogen and deuterium OH discharges, SOL profile measurements of helium plasmas with a fast reciprocating probe were made in OH discharges at IP=1.2/2 MA and BT=2.1/3.5 T. In the case of the same electron density, SOL density profiles of helium plasmas were similar to those of deuterium plasmas just before occurrence of the divertor MARFE. The radiation loss power from the divertor plasma was kept constant without disruption in the helium discharge with high density plasma (the line averaged electron density ~3.2x1019 m-3).

Radiative divertor experiments with neon gas puffing in hydrogen minority ICRF heating discharges were carried out to demonstrate compatibility of the radiative divertor with central heating plasmas at IP=2 MA, BT=3.4 T and PIC=3 MW. The radiation loss power from the main and the divertor plasmas increased after the neon gas puffing. And the detachment of the divertor plasma were observed.