Magnetization as a critical defining parameter for strand in precision dipole applications - Implications for field error and F-J stability

In hadron accelerators, between low energy particle injection and beam accu mulation, the guiding dipoles are ramped at some rate dB/dt. Both at inject ion and during ramping the static and dynamic magnetizations of the magnet windings introduce multipolar distortions into the beam-line field. Dynamic magnetization, controllable by cable design, is estimated and used to prov ide a criterion against which to evaluate the allowable magnitude of static (persistent-current) magnetization, M, from a field-quality standpoint. Th e Ms of NbTi and advanced Nb3Sn conductors are compared and with regard to the latter the question of flux-jump stability is explored. A magnetization criterion for such stability is presented and compared to experiment. It i s noted that since DeltaM is proportional to critical current density, Jc? and the strand's effective filament diameter, d(eff), the latter has freque ntly been specified as a critical parameter, although it will need to be re -specified with every increase in J(c). It is pointed out that although in the manufacture of MF Nb3Sn composites d(eff) will continue to be useful as a processing parameter in that it gauges the extent to which changes of pr ofessing conditions change the degree of interfilamentary bridging, and is measured by comparing the magnetic and transport-measured J(c)s, the most u seful information is embodied in the results of the magnetization measureme nt alone.