Study of plasma current start-up of the middle-sized tokamak with force-balanced coils

For a high held tokamak device, we have developed force-balanced coils (FBC s) which have nonuniform-pitch multi-pole helical-configuration to reduce c entering electromagnetic forces without using cancellation coils. As a supe rconductivity magnet, the FBC configuration is favorable to the achievement of high critical current densities because of a J(c)parallel toB effect. I n the tokamak operation with the FBCs, the rise of the toroidal held synchr onizes with the plasma current ramp up because the FBCs function both as to roidal field coils (TFCs) and as primary coils for ohmic heating. The torsi onal force exerted on the FBCs is comparable and the net centering force is reduced to 20% compared with those on conventional TFCs of the same dimens ions. (C) 2000 Elsevier Science B.V. All rights reserved.