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Fusion Plasma Research


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July 1998


The newly established coefficient matrix for the real time shape control improved the controllability of triangularity. Toward the steady state operation with high core plasma performance and divertor radiative cooling, the multiple feedback of neutron production rate, line density and divertor radiation power was demonstrated for the first time by using neutral beam power, main plasma gas puffing and divertor gas puffing as the actuators. Dependence of halo current on plasma density and temperature during the current quench phase was studied in detail by applying deuterium, He, Ne and CH4.

By increasing triangularity up to 0.48 at plasma current of 1MA, sustainable normalized beta was improved up to 2.5 - 2.7 at the low safety factor region (q95~3.2). The role of plasma toroidal rotation on energy transport in H-mode was studied in detail by changing the momentum input and its profile. When the plasma rotation direction is parallel to the plasma current, thermal energy confinement is 10% higher than that in the case of opposite rotation direction.


The current drive performance with the negative-ion-based neutral beam (NNB) injection was compared by changing the plasma position. The NNB-driven current of 370 kA was obtained in a inward-shifted plasma and the driven current was decreased to 270 kA when plasma was shifted outward. It is because the NNB beam has a longer trajectory in the core region in the inward-shifted plasma than in the outward-shifted plasma.

In the lower hybrid current drive (LHCD) of revered-shear plasma, LH waves coupled well with ELMy H-mode plasma in the revered-shear configuration. The safety factor in the core region decreased slower by LHCD than that without LHCD.

Alfven eigenmodes were investigated by injecting NNB into plasmas with low toroidal magnetic field of ~1.5 T. Magnetic fluctuations with n=1 in the frequency range of toroidal Alfven eigenmodes (TAE) were detected when the NNB of ~3 MW was injected at 350 keV. The mode frequency changed faster than that expected from the change in electron density.


In order to estimate diffusivity and convection velocity of impurity ions in ELMy H-mode plasma, gas-puffing modulation experiments were performed using He, Ne and CH4 gasses. Modulations in He and Ne ion densities were clearly observed. However, the modulated C ion density was not observed because of large background C ion density. Detailed analysis is in progress.