The CIT will require a liquid-nitrogen-cooled, pulsed poloidal field coil system for plasma heating, shaping, and control. The central solenoid will have a bore diameter of 0.8 m, a height of 4.8 m, and a central field of 23-256 T. Geometric restrictions are such that an aggressive structure concept is required. Two options are being considered for the machine. The first would require a self-supporting central solenoid consisting of a stack of explosively bonded copper/Alloy-718 plates with a copper/Alloy-718 ratio of 50/50. Each plate is cut into eight turns by a water-jet cutting process. Features of this design are presented along with selected results from an R&D program under way. Full-scale plates have been fabricated and cut, and prototypical mechanical and electrical joints have been tested. The other machine design option would allow the central solenoid to receive partial support from the TF (toroidal field) coil system. In this case the operating scenario and stresses are substantially different. R&D tasks have been started to evaluate conductor lifetime under simulated operating conditions for alumina dispersion strengthened (ADS) copper. Explosively bonded copper/Alloy-718 plates remain an option, but with a substantial increase in the ratio of copper to Alloy 718 to 70/30. The status of test results and plans for these materials is given

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.

SHORTFORCE is a series of Fortran programs that was developed to facilitate failure-mode and protection analyses of multiple coil/multiple circuit magnetic systems. The package allows rapid turnaround of alternate fault scenarios with emphasis on graphics to allow model verification and display of output results. Some of the features of the package are illustrated and calculated results are compared with data available from an existing superconducting magnet system. The assumed location of the short in the coil allows estimation of the short resistance and the magnitude of the threshold power level for normal-zone initiation by comparing the numerical results with the time intervals determined from voltage measurements. The rate of change of the resistance for a propagating and recovering normal zone is postulated along with the value of heat generation for which recovery could begin. These assumptions lead to good qualitative and quantitative agreement with measured voltage data.

A magnet failure which is potentially catastrophic in the sense that structural components fracture and the winding suffers extensive plastic deformation can be "safe" under special conditions. It may be desirable to limit operating current densities to levels at which the winding could act to limit magnetic to kinetic energy conversion. A solenoid model was used to analyze and determine the important governing parameters in the failure and discharge process. The conclusions are: (a) A protective circuit reaction involving resistive dissipation following a major structural failure is unlikely to be effective on a fast enough time scale in high current density windings. (b) Windings with low enough current densities can absorb the total load following structural failure, thus limiting the kinetic energy conversion process, although this might involve substantial yielding and deformation of the winding. (c) Protective circuits involving inductive energy transfer can respond fast enough to limit the kinetic energy conversion process in high or low current density configurations and are effective provided they are well coupled to the primary circuit.

- A general technique is presented for placing the passive elements and active coils in the most effective postions for stabilizing vertical plasma motion. General contours of effectiveness are given and then applied to a specific tokamak design

The rapid decay of magnetic flux associated with a plasma disruption induces voltages and currents in conducting bodies which are nearby. Recent tokamak designs utilize toroidal shells or shell segments near the plasma which are divided into sectors for assembly and maintenance purposes, but which may have electrically conducting paths toroidally in order to provide vacuum boundaries. The generation of voltage across sector gaps is a potential problem in the form of arc initiation with material damage. In addition, the induced currents interact with their own fields or fields from the TF or PF coils to generate electromagnetic loads which require consideration from the structural standpoint. The examples presented in this report were generated as part of the FED/INTOR reactor design study to illustrate the form and magnitude of these induced current effects and some of the machine characteristics which govern their behavior.

The highly elongated plasmas associated with divertor operation in the tokamaks are subject to a strong axisymmetric instability. A combination of passive loops and active feedback coils are needed for control of vertical plasma position. Development of design techniques for this coil system are underway using two techniques. First, simplified models are used which lead to generalized diagrams for evaluation of the relative effectiveness of different locations for active or passive elements. These plots and the associated methodology are generally applicable to tokamak design. At the second level, a more detailed computer model, incorporating the specific machine configuration and constraints, is used to study the optimal active coil and passive element characteristics.