LBNL, Berkeley
Funding: This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Nuclear Physics Division of the U.S. Department of Energy under Contract DE AC03-76SF00098.
The development of the superconducting 28 GHz ECR ion source VENUS at the Lawrence Berkeley National Laboratory (LBNL) has pioneered high field superconducting ECR ion sources and opened a path to a new generation of heavy ion accelerators. Because of the success of the VENUS ECR ion source, superconducting 28 GHz ECR ion sources are now key components for proposed radioactive ion beam facilities. This paper will review the recent ion source development program for the VENUS source with a particular focus on the production of high intensity uranium beams. In addition, the paper will discuss a new R&D program started at LBNL to develop ECR ion sources utilizing frequencies higher than 28 GHz. This program addresses the demand for further increases of ion beam intensities for future radioactive ion beam facilities. The most critical technical development required for this new generation of sources is the high-field superconducting magnet system. For instance, the magnetic field strengths necessary for 56 GHz operation produce a peak field in the magnet coils of 12-14 T, requiring new superconductor material such as Nb3Sn. LBNL has recently concluded a conceptual, comparative design analysis of different coil configurations in terms of magnetic performance and has developed a structural support concept compatible with the preferred magnetic design solution. This design effort concludes that a sextupole-in-solenoid ECR magnet structure (VENUS type) is feasible with present Nb3Sn technology, but that an inverted geometry (solenoid-in sextupole) exceeds the capability of Nb3Sn superconductors and can be ruled out as candidate for a 56 GHz ECR ion source.
