Design analysis of a cryostable sector magnet for superconducting separated-sector cyclotron

摘要

A full-scale prototype of a superconductingsector magnet is under construction at RIKEN to assessthe magnet design conceived and to gain operationalexperiences of the magnet system. In this paper somedesign features of the prototype and viablealternatives are investigated chiefly through quenchanalysis. The coils are designed to he cryostable. Thecryostability, however, may degrade when a helium vaporis trapped inside the coil vessel. Such an event islikely because the vessel is largely packed withsupporting materials to elevate the coil stiffness, andbecause the vessel is configured horizontally flat.Assuming the existence of an uncooled conductor,critical lengths of a normal region and minimum quenchenergies were numerically studied. Another salientfeature of the prototype is the use of iron pole piecesat 4.5 K to effectively enhance the magnetic fields andto reinforce the mechanical structure. However, due toclose coupling of the pole pieces with the coils, AClosses are rather substantial. They were computed toquantify the energy shift during a quench and to lookinto the possibility of rapid spread of a normal region.The proposed high-field cyclotron comprises sixsuperconducting separated-sector magnets in which thetotal stored energy amounts to 400 MJ at maximumexcitation. An optimal arrangement of coil connectionhas been pursued in the design of the quench protection system.