An Engineering Design Study of the Dipole Magnet Cold Mass End Shell for the Superconducting Super Collider

Abstract

The dipole magnets are the major component of the Superconducting Super Collider accelerator. The 50 mm collider dipole cold mass shell is a pressure vessel. The design and operation of the dipole magnet must first consider safety, an area of no compromise¹. The most critical stresses in the dipole shell are found in the end shell. The present analytical result indicates that the critical stresses can be effectively reduced by employing an end yoke to support the end skin

The dipole shell is designed not only as a pressure vessel, but also as a preloading device for obtaining optimum performance of the superconducting dipole magnet. Therefore, an optimum design of the end shell is essential to minimize quench occurrence as well as to realize long-term operational safety and reliability of the dipole.

The dipole skin, collar, and yoke can be designed to work together to reduce the following undesirable effects: (1) reduction of the critical current density due to over-stressed coils; (2) generation of frictional heat due to the micro-motion of the coils under Lorentz forces; and (3) over-straining of the conductor insulation leading to short circuit.

From the point of view of safety, the stress limit for the shell must be kept within a low cycle fatigue limit with adequate margin of safety. The low cycle fatigue limit of the dipole skin, especially in the area of longitudinal seam welds, should be established in the 4.2 K thermal environment. Rigorous analyses and tests are needed to predict the adequate margin of safety. Past studies indicate that the critical skin stresses are located in the area where the body yoke “falls off” to magnet ends. Various design modifications of the end skin were proposed to reduce the high local stresses.^{2, 5, 6}

Critical skin stresses found in the end skins can be minimized by utilizing an end yoke extending from the body yoke to the end plate. Effect on the field quality by addition of the end yoke is not considered in the present analysis.

Operated by the Universities Reasearch Association, Inc., for the U.S. Department of Energy under Contract No. DE-AC02-89R40486.

This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-76CH03000.