ECH Plasma Experiments on an Internal Coil Device with a High Temperature Superconductor Coil

Self-organization related with relaxation phenomenon is playing an important role in various aspects of magnetic confined plasmas. Recently a relaxation theory including the plasma flow has been developed by Mahajan-Yoshida, and a new relaxation state has been identified. The two-fluid relaxation condition is given by + (V/V_A)² = const. To study a self-organized structure with strong plasma flow, we have introduced an internal coil device. By inducing a radial electric field with appropriate methods, we could drive a toroidal plasma flow, and confine a high beta plasma in a core region. The internal coil device Mini-RT with a high temperature superconductor(HTS) coil(Rc=0.15m, Ic=50kA) has been constructed. The vacuum chamber is 1 m in diameter and ~0.7 m in height. The magnetic field strength near the internal coil is around 0.1 T, and a radio-frequency wave of 2.45 GHz is applied for the plasma production. We have started ECH plasma experiments with the coil supported mechanically. The electron density, which has a peak near the internal coil, is of order 10¹⁶ m^-3, reaching the cut-off density of the microwave. While, the electron temperature is of order 10 eV with a broad profile. Estimated energy confinement time is of order 10^-(5-6) sec. The levitation experiment of the HTS coil has been carried out. The position of the HTS coil is measured with laser sensors, and is feedback-controlled with the levitation coil current. We have succeeded to levitating the HTS coil during one hour with an accuracy of less than 20 m. A preliminary experiment for the plasma production at the floating condition of the HTS coil has been initiated. It is affirmed that the levitation system works well and plasma with separatrix configuration is produced.