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 it is 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 ΔM is proportional to critical current density, J_c, 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 processing conditions change the degree of interfilamentary bridging, and is measured by comparing the magnetic and transport-measured J_cs, the most useful information is embodied in the results of the magnetization measurement alone