Performance of present high charge state ECR ion sources and challenges for next generation sources

Summary form only given. Electron Cyclotron Resonance (ECR) ion sources produce high charge state, intense heavy-ion beams for many high energy and nuclear physics accelerators. Several third generation sources utilizing superconducting magnet structures and gyrotrons operating at frequencies greater than 20 GHz are now in operation. Recent results from the LBNL 28 GHz ECR ion source VENUS include 3000 eμA of O⁶⁺ and more than 400 eμA of U³³⁺. New accelerators under design will require even more intense beams and designs for a next generation ECR ion source are being developed. Many years ago, R. Geller predicted that the current of ECR ion sources should scaled as the square of the RF frequency when the magnetic confinement fields are scaled linearly with the frequency [Geller, R., et al., 1987] and this has been shown to hold up to at least 28 GHz. To meet the requirements of the new facilities, next generation ECR ion sources are being designed to operate at roughly 50 GHz with axial magnetic fields up to 7 T and radial fields up to 4 T. This will require advanced magnet structures, perhaps utilizing Nb3Sn and new coil geometries. [Lyneis, C., et al., 2011] In addition, to couple the short wavelength, high power microwaves into the ECR plasma may require conversion of the gyrotron power to HE11 or gaussian TEM₀₀₀ waves prior to being launched into the plasma. In this paper the operation of third generation ECR ion sources and the concepts and challenges for a next generation ECR source will be discussed.