Construction of the superconducting ECR ion source Venus

A new, very high magnetic field superconducting ECR ion source, VENUS, is under development at the LBNL 88-inch cyclotron. It will boost the maximum energies and intensities for heavy ions from the cyclotron particularly for ions with mass greater than 60. It will also serve as R and D ion source for the proposed rare isotope accelerator (RIA) project in the US, which requires up to 10 pμA of U30+. The superconducting magnet structure consists of three solenoids and six racetrack coils with iron poles forming the sextupole. The coils are designed to generate a 4 T axial mirror field at injection and 3 T at extraction and a radial sextupole field of 2.4 T at the plasma chamber wall. Test results of the magnet coils, which exceeded design requirements with minimum training, are presented. The magnet assembly with its cryostat will be enclosed by an iron shield and therefore must be designed to withstand any possible forces between coils and iron, which can be as high as 3.4.105 N (35,000 kgf). The low energy beam transport line (LEBT) and mass analyzing system of the ion source is designed to transport a proton-equivalent current of 25 mA at 20 kV extraction voltage. The design of the ion source and LEBT will be discussed. (orig.)