Investigations on Confinement Improvement by Supressing Microscopic Instabilities in Toroidal Plasmas

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The objective of this research is to develop the method to reduce the anomalous transport. Based on the working hypothesis that the cross field transport is driven by microscopic instabilities, we study the way to reduce the transport coefficient by suppressing the microinstabilities.By this research project, we have obtained a new theoretical result on the anomalous transport in Torsatron/Heliotron configurations. The theory includes the roles of the current diffusivity. This new model formula, though appricable only to the systems with the magnetic hill, explains the majority of the experimental observations on confinement in such devices. If further verification will be gained through future examination with experiments, this method will give a guiding principle to predict a cofiguration, in which anomalous transport is reduced. In tokamaks, it has been shown that the toroidicity is a critical element to cause the anomalous transport. The theoretical model can be extended to systems with the magnetic well, by employing the ballooning formalism. The extension and generalization are left for the future study.By studying the current diffusicity, we have obtained a new phsics picture of the disruptive phenomena. The mechanism of the accelerated growth of the global instabilities is presented. The magnetic braiding by the global instabilities gives rise to the enhanced current diffusivity, which then increases the growth rate of the mode.In summary, this research project has shown a considerable progress in the original programme as well as in the unexpected area of the research.