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A computer program that simulates quenches in superconducting multisectioned solenoids is described. The winding of each section is assumed to be a close-packed hexagonal arrangement of wire impregnated with epoxy resin. The program predicts the current, terminal voltages, and temperature distribution for each section of the coil. The normal zone is assumed to originate at the high-field region of the winding and to grow radially and axially by heat conduction through the insulation and epoxy. Azimuthal propagation being very rapid is assumed to be instantaneous. Transverse propagation is calculated from an empirical correlation based on measurements in small samples of conductor configured to simulate coil windings. The model is used to predict the current and terminal voltages in two- and four-section solenoids. The results show good agreement between the predictions and quenching experiments.<>

An analysis has been performed to investigate the limits of high field commercial tokamak reactors. Variations of the maximum mechanical stress, the major radius and the performance parameter (where B0is the magnetic field on axis and a is the minor radius) have been investigated to evaluate the potential impact of higher strength structural materials and higher field superconductors. For fixed values of major radius and stress, the tokamak parameters have been chosen such as to optimize machine performance. Increasing values of allowable stress correspond to decreasing capital cost and may be an effective approach to economic commercial fusion. The paper discusses prospects of using very high strength structural materials to provide a sufficiently high field for Ohmic dominated heating to ignition in power reactors with a major radius of about 6 m.

The Compact Ignition Tokamak requires a liquid-nitrogen-cooled, pulsed poloidal field coil system for plasma heating, shaping, and control. It will dissipate about 1780 MJ in a total pulse length of 22 s and will require a peak power of 390 MW. The central solenoid will have a bore diameter of 0.68 m, a height of 2.4 m, and a central field of almost 22 T. Geometric restrictions are such that an aggressive structural concept is required; hence, the coil consists of a stack of explosively bonded copper/steel plates. Each plate is cut into eight turns by a water-jet cutting process. Features of the design and selected results from an R&D (research and development) program which is underway are reviewed.<>