Superconducting Magnets in Fusion Reactors

Abstract

A fusion reactor is an artificial sun created under laboratory conditions of high temperature and pressure to produce inexhaustible energy. When two nuclei of hydrogen isotopes are forced to fuse, under high temperature and high pressure, the reaction produces huge amount of energy and the heavier atoms of helium. The tokamak concept for magnetic confinement of plasma in a fusion reactor made the use of superconducting magnets most attractive and a natural choice. This chapter gives an account of the fusion process, the Lawson-Criterion for realizing ‘ignition’, different methods of plasma confinement and the superiority of tokamak concept. In a tokamak plasma is confined in a torus by an axial field generated by a set of toroidal coils distributed around the torus and a poloidal field generated by a set of poloidal coils. A high field central solenoid induces current in the plasma to heat it to high temperature through ramping of the field. This current in turn also produces poloidal field. We discuss the superconducting magnet systems built for most important fusion reactors so far, namely, T-7 of Russia, Tore Supra of France, JT-60 SA of Japan, KSTAR of Korea, EAST of China and SST-1 of India. The magnet systems of ITER, has been discussed in greater details. Two tokamaks, namely, TFTR of USA and JET at Culham UK both using normal magnets have also been included for they had many firsts and the data collected from them contributed significantly to the design of ITER. Two more futuristic reactors, the stellarator W7-X being built in Germany and IGNITOR an Italian–Russian joint fusion reactor being built in Russia have also been included towards the end of the chapter.