Considerations on the design of 4MJ pulsed superconducting magnet

Some considerations on structural and thermal designs on 4MJ pulsed superconducting magnet are described. By using a model which simulates one of the double pancake coils of the magnet, the turn-to-turn propagation of electromagnetic force is analysed. It is clarified that the force would hardly be transmitted when the Young's modulus perpendicular to the flat surface of the cable is small, that is, about a few hundred kg/mm2 and that a Young's modulus of more than 1,000 kg/mm2 will be required in order that the force may be transmitted sufficiently. The winding rigidity in axial direction of the magnet is also studied. When the magnet is regarded as an elastic body, the characteristic frequency is calculated to be about 25 Hz. It is sufficiently high as compared to an operating frequency of the magnet under consideration, and hence there is no problem on the dynamic response of the windings to the operating frequency. In the thermal desigh of the magnet, a horizontal velocity of the helium bubbles which exist in the 3 degree-tapering cooling channels is calculated under an assumption that they will form a so-called slug-flow, and it is made clear that the horizontal velocity becomes higher than a rising velocity and is around 7 cm/sec. Therefore, bubbles generated around the middle portion of the windings will be evacuated fast enough to the outside of the magnet. (author)