VENUS Ion Source
VENUS (Versatile ECR ion source for NUclear Science) is a next generation superconducting ECR ion source, designed to produce high current, high charge state ions for the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory. VENUS also serves as the prototype ion source for the RIA (Rare Isotope Accelerator) front end.
The goal of the VENUS ECR ion source project as the RIA R&D injector is the production of high current medium charge state uranium beams (U30-34+). As an injector ion source for the 88-Inch Cyclotron, the design objective is the production of very high charge state beam (U48+, Xe44+). To achieve these ambitious goals, the VENUS ECR ion source has been designed for optimum operation at 28 GHz. Since then, it has produced world record ion beam intensities, some of which are listed in the table below.
Mechanical layout of the VENUS Ion Source
The magnetic confinement configuration consists of three superconducting axial coils and six superconducting radial coils in a sextupole configuration. The nominal design fields of the axial magnets are 4T at injection and 3T at extraction; the nominal radial design field strength at the plasma chamber wall is 2.2T, making VENUS the world's most powerful ECR plasma confinement structure.
The plasma chamber is made out of a double-walled aluminum tube with water cooling-channels in between. Three or more off-axis microwave feeds as well as ovens and a biased disk are inserted from the injection spool. The end walls of the iron shielding-yoke are designed to reduce the magnetic stray-field outside of the yoke to <50 Gauss.
Cutout drawing of the VENUS superconducting coil configuration
The superconducting coil configuration of the 3rd generation ECR ion source is designed to generate magnetic fields considerably greater than those of any existing ECR ion source. The two outermost solenoids produce an axial magnetic mirror field, whose center strength can be lowered by a third, oppositely polarized solenoid. The sextupole field is generated by the six racetrack coils wound around a pole piece made of iron and aluminum.
Design characteristics of the VENUS magnet structure
Characteristic field data - as calculated by the three-dimensional code TOSCA - are summarized above. The design and fabrication of the magnet structure is based on a collaborative effort between the 88-Inch Cyclotron of the Nuclear Science Division and the Supercon Group in the Accelerator and Fusion Research Division at Lawrence Berkeley National Laboratory.