Recent progress in a Josephson computer technology is reviewed. A Josephson computer is very attractive because Josephson digital circuits have the potential for realizing LSI circuits with extremely high performance in both circuit speed and power dissipation. Recently, various Josephson LSIs, such as processors and memories, have been made successfully with Nb or NbN junctions, particularly in Japan. These junctions exhibit high reliability for thermal cycling and long term storage, and have a good uniformity of the Josephson tunnelling current due to the tri-layer junction sandwich process. On the basis of such progress in Josephson IC technology, research, on Josephson computers in which Josephson memories are installed with a processor, is now under way.
A superconducting magnet, not fully stabilized, has instability that a normal zone, induced by a certain local disturbance, may lead to normal transition of the magent as a whole. Approximate evaluation of propagation of normal zones in superconducting wires is outlined and some remarks are made for anisotropic propagation in magnets. As a typical example, an analytical expression proposed by Wilson is presented and is compared with experimental results in bare and insulated wires. Basic ideas of magnet protection from mechanical and thermal damages in quench process are explained in two types of protection systems by an external resistor and “quenchback.” New aspects of magnet protection are also discussed in prospective applications of superconducting magnet.