Simulation studies of space-charge-dominated beam transport in large-aperture ratio quadrupoles

Summary

For many cases of interest in the design of heavy-ion fusion accelerators, the maximum transportable current in a magnetic-quadrupole lattice scales as (a/L)², wherea is the useful dynamic aperture andL is the half-lattice period. There are many cost benefits in maximizing the usable aperture which must be balanced against unwanted effects such as possible emittance growth and particle loss from anharmonic fringe fields. We have used two independent simulation codes to model space-charge-dominated beam transport both in an azimuthally pure quadrupole FODO lattice design and in a more conventional design. Our results indicate that careful matching will be necessary to minimize emittance growth and that (a/L) ratios of 0.2 or larger are possible for particular parameters.