The development of MHD generators is supported in USA by the Energy Research and Development Administration. Several paralell projects like U-25 (a joint work with USSR), CDIF project and AEDC project are currently being carried out. These projects may be considered as the phase I of the MHD projects of USA. In this paper the design, manufacturing and the test of U-25 bypass superconducting magnet (phase-I) and a conceputual design for the future full scale superconducting magnet (phase-III) are discribed especially among the works done along this line of activities.
In large-scale refrigeration for superconducting magnets and power transmission cables, several types of fluid oscillations have been observed; thermal acoustic, mass flow, and temperature oscillation caused by coupling of heat exchangers. A considerable amount of work has been so far concerning to the former two types of oscillations, but the latter type of oscillation has not been studied yet. In this paper, the state equations are formulated in the form of simultaneous ordinary differential equations, and transfer functions of a refrigeration system are derived by Laplace transformation. The characteristic equation is analyzed and the existence of temperature oscillation caused by coupling of heat exchangers is proved. The temperature oscillation is also observed in our experiments.
With increasing of the magnetic stored energy in superconducting coils, the risk of their transition into normal conduction may be getting abnormally higher. In the past the protection methods to prevent superconducting coils from their transition faults were developed, and some of them have been practically used in actual superconducting coils. In this paper, new types of protection methods are proposed: 1) constant DC voltage power line energy sink, 2) precharged capacitor energy sink, 3) prerotating DC motor energy sink, and their performances and how to select parameters of protection systems are also presented. In an analysis, as an example of protection criterion we consider the current-decrement time constant of coil circuit made of NbZr of 0.01 inches in diameter, as stated in the Smith's paper. The precharged capacitor and prerotating DC motor energy sink systems would be thought to be practicable for small and medium scale superconducting coils, and on the other hand the constant DC power line energy sink system constructed of a thyristor converter-inverter would be practically suitable for large scale superconducting coils.