CT Injection Experiment in JFT-2M

A compact toroid (CT) injector is considered to comprise one of the advanced refueling methods for the fusion reactor. In JFT-2M, it was demonstrated for the first time that a CT injected into a neutral beam-heated plasma penetrated deeply into the plasma and caused a rapid increase in the electron density. We also observed interesting motions such as shift and reflection of the injected CT plasma as well as magnetic fluctuations induced just after CT injection. A power spectrum analysis suggested that this fluctuation was related to magnetic reconnection between the CT plasmoid and the toroidal field. We also modified the shape of the CT injector electrodes to improve CT injection efficiency. As a result, the CT parameters were superior to those of previous experiments, and the operational window became broader. Finally, it has been successfully demonstrated that a CT could be transported smoothly through curved drift tubes, which is one of the key technologies to avoid adverse effects of the toroidal field and to extend flexibility of the design and layout of the CT injector to access larger devices