PURPOSE: To prevent generation of a gap between coils and beam duct and enhance the intensity of a magnetic field by furnishing a gap between a pair of yokes which has a size greater than twice of the difference between the coil contracting amount and the yoke contracting amount in the superconductively cooled condition. ;CONSTITUTION: When a wiggler device is cooled to the operating temp. of superconductive coil, coils 5, 6 and yokes 1, 2 contract according to their respective coefficients of thermal contraction. The interval of the yokes 1, 2 is decreased by the attracting force between coils 5, 6 confronting one another generated by current feed and the fastening force of the yokes 1, 2. This decrease of the interval is twice the difference between the thermal contracting amount of the coils 5, 6 in the z-direction and the thermal contracting amount of the portions 1c, 2c of the yokes 1, 2. If therefore the gap δ between the confronting surfaces of the yokes 1, 2 is made greater than twice the difference in the thermal contraction between the coil and yoke, it can be absorbed with the gap δ lessened, and no gap will be produced between the coils 5, 6 and beam duct 7.;COPYRIGHT: (C)1994,JPO&Japio
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