The design of end magnetic system coils for `AMBAL-M´

The end of the AMBAL-M tandem mirror plasma trap is an axially symmetric plug with a semicusp MHD (magnetohydrodynamic)-expander. The plug field is formed by a pair of coils, and the semicusp field is formed by another pair of anti-parallel coils. The axial dimension of the end magnet system is 3.2 m, and the middle diameters of the coils are from 0.6 to 1.1 m. The operation mode features a 24-kA current, a 1.5-s effective pulse time, and a repetition rate of 1 pulse per 15 min. The coil design is described. The coil is a packet of parallel modules whose conductor is a copper ribbon with a 500-mm² cross section, and water-cooled copper disks between them for heat removal. The heat calculation principles are given. The characteristics of the smaller semicusp coil with regard to its location in a vacuum are noted. Some manufacturing problems are also described