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 accumulation, the guiding dipoles are ramped at some rate dB/dt. Both at injection 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 provide a criterion against which to evaluate the allowable magnitude of static (persistent-current) magnetization, M, from a field-quality standpoint. The 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 is noted that since DeltaM is proportional to critical current density, Jc? and the strand's effective filament diameter, d(eff), the latter has frequently 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 professing conditions change the degree of interfilamentary bridging, and is measured by comparing the magnetic and transport-measured J(c)s, the most useful information is embodied in the results of the magnetization measurement alone.