High beta plasma confinement study on a small torus device with a floating high temperature superconductor coil

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We are aiming at studying high-beta plasmas on a small torus device with a high temperature superconductor coil. From the viewpoint of plasma experiment and device operation, we have employed a high temperature superconducting cable Bi-2223, which has a large heat capacity in comparison with a low temperature superconductor. This is a first challenge for applying the high temperature superconductor coil in fusion plasma devices, and there are few challenges for the feedback levitation of the high temperature superconductor coil.We have started several R&D issues for the internal coil device Mini-RT ; e.g., the demonstration of the levitation with the miniature device FB-RT, the design and fabrication of the persistent current switch (PCS) and the demonstration of the persistent current operation, and developments of demountable transfer tube and current feed-through.In the Mini-RT device, we have successfully levitated the high temperature superconductor coil with an accuracy of 10 micrometer during a hour. Since the typical magnetic field is 0.1T around the internal coil, the plasma is produced and heated by the Electron Cyclotron Heating (ECH) with the microwave of 2.45 GHz. The plasma density is (5-7)x10^<16> m^<-3>, and is reaching at the cut-off density of the microwave. The density profile has a peak near the internal coil. The electron and ion temperatures are 10 eV and 1 eV, respectively.