DESIGN, FABRICATION, AND PROPERTIES OF MAGNETICALLY COMPENSATED SSC STRANDS

Nonsuperconducting saddle magnets can in principle be designed to produce an undistorted dipolar magnetic field, but if they are wound from superconducting strands, residual magnetization, M(R), (i.e. "persistent current") resident in the filaments causes a multipolar distortion of the desired field. Numerous ways of reducing this magnetization or its effect, at both the strand-design and magnet-design levels, have been proposed. Central to the various possible "magnetization-compensation" approaches is the fact that during the operating (field-increasing or "shielding") branch of the SSC magnet's excitation cycle, M(R) is mostly diamagnetic. Such a negative magnetization can obviously be neutralized by the inclusion within the magnet of strategically placed ferromagnetic elements. Early studies have suggested that magnetization compensation could be achieved through the insertion of bulk pieces of a ferromagnetic material into the dipole "wedge". But in this work we describe how the ferromagnetic compensator, in this case Ni, can be associated with the composite strand itself, either in the form of replacement filaments or as an electroplated coating on the outside surface.