Plasma production and levitation experiments of a high-temperature superconductor coil in a Mini-RT internal coil device

Plasma is produced using a 2.45 GHz microwave in a Mini-RT internal coil device, where a high-temperature superconductor is employed. The radius of the internal coil is 0.15 m and its weight is 16.8 kg. The maximum coil current is 50 kA, and the typical magnetic field strength at the internal coil is 0.1 T. First plasma experiments were carried out using a mechanically supported coil, and a typical plasma density in the range of 1016 m-3 was produced. When the internal coil current is decreased to less than 10 kA, plasma cannot be produced because of the disappearance of the electron cyclotron resonance layer of the 2.45 GHz microwave. Concerning to the levitation experiments of the internal coil, the coil position is monitored with laser sensors, and the levitation coil current is feedback-controlled. The HTS coil has been levitated for a period of one hour with an accuracy of 10 micrometers. Plasma production with a floating coil has been successfully initiated. (author)