Practical superconductors for accelerators - filamentary conductors

All superconducting accelerators to date have used magnets wound from Rutherford cable. In this first of two lectures, we describe the filamentary superconducting wires used within a Rutherford cable. To discuss the reasons for this fine filamentation of the superconductor, we first describe the critical state model and then use it to show how persistent currents in the superconductor produce magnetization effects, which cause field errors. Coupling between the filaments is then discussed, together with the criterion for twisting to de-couple the filaments. Finally the relationship between magnetization and ac losses in changing fields is described.