First coil energization
Today the first of the superconducting tokamak coils was supplied with power. Equilibrium field (EF) coil 2, located towards the top of the tokamak, was supplied with up to 1 kA by about 21:00 JST. The EF 2 magnet is almost 10m in diameter and weighs over 30 tonnes. This is a major project milestone, following the recent completion not only of the cooling down of the magnet system to 4.5 K but also the completion of the combination testing of the power supplies. Today after confirming the temperatures, pressures and flow rates of the cryogenic distribution system and testing the effects of the quench protection systems with synthetic signals, it was finally possible to send current to the coils whose field will soon confine JT-60SA plasmas. A quench occurs when a superconductor loses its ability to carry current without resistance. In these circumstances the magnets must be discharged rapidly to avoid damage. In the next days the current supplied to EF2 will be gradually increased as the quench detection circuits and the power supply controllers are tuned. The stainless steel vacuum vessel has a double wall and is heated by passing hot nitrogen gas between the inner and outer shells. The gas is heated electrically in the torus hall basement and is circulated in a closed loop. The baking of the vacuum vessel causes a substantial increase in the heat radiated to the thermal shield around the cryogenic magnets and a corresponding increase in liquid nitrogen consumption by the cryoplant keeping it cold.