Design study on future accelerator magnets using largely keystoned cables

In the near future, superconducting magnets with a small beam aperture will be required for high-energy proton colliders. When coils are designed to be self-arched over a small beam pipe, the magnet construction is simplified both in the winding procedure and in the field quality control. Fabrication of these coils requires cables with large keystone angles. A braid-in-strand structure was devised to produce these cables. Two types of self-arched coils were found to produce good field homogeneity. Prior to construction of a whole magnet, a straight section of a circular-aperture magnet was fabricated to obtain detailed information on the cable position. Strand positions have been measured on the cross section of the coil. Magnetic field analysis is made on the basis of the position of the strands