Study on the AC Magnetization of LHC Type of Rutherford Cables

Abstract

In accelerator magnets, and especially at low excitation values, the field errors are mainly determined by the filament hysteresis. To obtain an understanding of this hysteresis, measurements are normally performed on strands under the assumption that the magnetization of the cable is equal to the magnetization of the strands. In this paper a new test arrangement is described to measure the AC and DC magnetization of flat cables up to lengths of about 13 cm. Magnetization measurements on various NbTi keystoned Rutherford type of cables are presented. In order to investigate the influence of the geometry of the cable in terms of the strand and cable pitches, some strands are also separately tested in both their original (straight) and “cable” shapes. The field is applied parallel to the wide side of the cable. One can calculate for this case that the magnetization is mainly determined by the hysteresis of the filaments and the inter-filament coupling. For strands with a copper matrix the inter-strand coupling in the parallel field is negligible, even for relatively low inter-strand contact resistances. An experimental study of the inter-strand magnetization is only relevant if the transverse pressure on the cable under test conditions is about the same as the pressure in the coils in which the cable is used.