Development of a super-conducting levitated coil system in the RT-1 magnetospheric confinement device

The Ring Trap 1 (RT-1) device was constructed to explore a novel concept of plasma confinement. The plasma is confined in a dipole magnetic field produced by a high-Tc super-conductor (Bi-2223) coil that is levitated in the vacuum chamber. The major radius of the floating coil is 25 cm, and its weight is 110 kg. The field strength in the confinement region varies from 0.3 to 0.03 T. The conductor is first cooled to 20 K in the maintenance chamber, which is located at the bottom of the plasma chamber, after which it is charged to 0.25 MA. The floating coil consists of 12 pancakes and has a total of 2160 turns. After detaching the current leads and coolant transfer tubes, the floating coil is raised to the midplane of the plasma chamber, and is then levitated by a feedback-controlled magnet installed on the top of the vessel. Laser sensors measure the position of the floating coil. The super-conducting operation can be maintained for approximately 8 h before the coil temperature increases to 30 K. The current decay is 0.9% after 8 h. The first experiment using the RT-1 device was performed in January 2006. We have succeeded in levitating the floating coil and in producing plasma by injecting a microwave of 8.2 GHz (1.5 kW).