Patent Number: 042630967
Section: claims

1. In a device having a toroidal plasma containment vessel with walls confining a toroidal region encircling a central opening through the vessel, a toroidal coil system for producing a toroidal magnetic field in the vessel, said toroidal coil system comprising  fixed field generating linking coil means comprising at least one linking coil disposed in fixed relation to said vessel with the coil linking the vessel, each linking coil being formed of first and second sections with the first section passing through said central opening through the vessel and the second section completing the linking coil to link the vessel,  a plurality of movable unlinked field correcting coils each formed of first and second C-shaped sections joined to each other at their open ends with their bights spaced apart,  means for removably mounting the second C-shaped section of each movable coil adjacent said second section of one of said linking coils, with the plasma containment vessel disposed between the open ends of the respective first and second C-shaped sections, with neither C-shaped section passing through said central opening through the plasma containment vessel to link the vessel, and  means for passing electric current through said linking and movable coils in opposite sense in the respective adjacent second sections. 2. A toroidal coil system according to claim 1 wherein with said second C-shaped sections mounted adjacent said second section of a linking coil, said first C-shaped sections are substantially evenly distributed about the periphery of said vessel, and the net magnetic field strength at said adjacent second sections approximates the magnetic field strength at each of said first C-shaped sections when said means for passing electric current is energized. 3. A toroidal coil system according to claim 2 wherein said linking coils are disposed at respective azimuthal positions 180.degree. apart and said sections of said unlinked coils are substantially evenly distributed therebetween. 4. A toroidal coil system according to claim 2 wherein said first sections of said linking coils are substantially evenly distributed around said central opening.