Static and dynamic parasitic magnetizations and their control in superconducting accelerator dipoles

Long dipole magnets guide the particle beams in synchrotron-type high energ y accelerators. In principal Cu-wound DC-excited dipoles could be designed to deliver a very uniform transverse bore field, i.e. with small or negligi ble harmonic (multipolar) distortion. But if the Cu is replaced by (a) supe rconducting strand that is (b) wound into a Rutherford cable carrying a tim e-varying transport current, extra magnetizations present within the windin gs cause distortions of the otherwise uniform field. The static (persistent -current) strand magnetization can be reduced by reducing the filament diam eter, and the residue compensated or corrected by strategically placed acti ve or passive components. The cable's interstrand coupling currents can be controlled by increasing the interstrand contact resistance by: adjusting t he level of native oxidation of the strand, coating it, or by inserting a r ibbon-like core into the cable itself. Methods of locally compensating the magnetization of NbTi and Nb3Sn strand and cable are discussed, progress in coupling-current suppression through the use of coatings and cores is revi ewed, and a method of simultaneously reducing both the static and dynamic m agnetizations of a NbTi cable by means of a thin Ni core is suggested. (C) 2001 Elsevier Science B.V. All rights reserved.