Construction of a toroidal plasma confinement device with a floating internal coil for studying high beta plasmas

A new relaxation theory for high-beta plasma configuration has been proposed by Mahajan-Yoshida. For exploring this new relaxed configuration, we are constructing an internal coil device, called Mini-RT, with a high temperature superconductor (HTS) coil. Typical machine parameters are as follows; the major radius of the internal coil is 0.15 m and the coil current is 50 kA·turn. The vacuum chamber is 1 m in diameter and ∼0.7 m in height. We are planning to produce a neutral plasma with 2.45 GHz Electron Cyclotron Heating system. A strong plasma flow in toroidal direction is expected by introducing a radial electric field Er. A persistent current switch should be equipped in the floating coil, because the floating coil current is charged with the demountable electrode. Here A Ag-sheathed Bi-2223 HTS tape with 0.3 wt% Manganese has been successfully tested for the persistent current switch. The levitation control of the HTS coil is another important issue. We have fabricated a small HTS coil (0.04 m in radius, and 2.6 kA·turn), and succeeded in levitating it during a few minutes with an accuracy of 20-30 micrometers. (author)