Trim coil system design of a superconducting ring cyclotron

Abstract

The trim coil system of a superconducting ring cyclotron currently under design at RIKEN is composed of five sets of superconducting and twenty sets of normal-conducting coils. A major correction for isochronization of the magnetic field is accomplished by the superconducting coils, and a fine correction by the normal-conducting coils. For an optimal design of the system, a numerical procedure was developed to generate isochronous fields for design nuclei and consequently current settings on the main and trim coils, employing an iteration of a least-squares fitting to minimize orbital frequency errors. The main and normal-conducting coils can also be used to correct unwanted harmonic fields with sector dependent and/or radially localized excitations. The correction schemes were conceived for presumed error fields, alignment tolerances being estimated based upon beam optics requirements. On the other hand, a new trim coil design was envisaged, which comprises only superconducting trim coils. The subcoils in the present five-set design can be independently excited to replace the normal-conducting coils. This option may be more economical, but complications on the superconducting coil system raise a reliability concern.