Large Superconducting Tokamaks

Abstract

The magnetic field geometry for plasma containment receiving the most worldwide attention at the present time is the Tokamak System.

The main toroidal field in all existing machines and those at present being constructed is generated by an assembly of copper coils, often water cooled.

Design studies of power producing fusion reactors, however, show that this type of machine may only be economically viable if superconductors are used for this purpose.

The magnetic energy stored in the toroidal field of a 2500 MW(e) reactor will probably be greater than 10¹¹ joules and even in the next generation of experiments designed to demonstrate the ‘feasibility’ of fusion, will exceed 10¹⁰ joules. Due to the physical size and field strength of about 80 kG the forces and stresses will be much higher than ever before experienced. Pulsed fields for inducing the plasma current and stabilizing it will also react with the current in the coils giving rise to severe repetitive twisting moments.

Questions now being asked include: is it possible to use superconductors to meet all the technical and reliability conditions, can it be done economically and what development work must be done to bridge the gap between now and then?

These questions form the basis of the topics discussed in the paper.