Effect of the Plasma Chamber Radius on the High Charge State Production in an ECR Ion Source

Two versions of the 18 Gilz PHOENIX ECR ion source have been developed in the framework of the SPIRAL2 project. The former design (V2) has a compact plasma chamber volume of 0.6 liter with a diameter of 62 mm. A new design (V3) has been developed at LPSC with a larger diameter of 89 mm (chamber volume 1.4 liter) with enhanced pumping features. Since the two versions have nearly the same axial mirror structure and the same radial magnetic field intensity at the wall, it is of interest to compare their performances as a function of the plasma chamber radius. Experiments have shown an improvement of high charge state production of Argon between V2 (45 mu A Ar14+, 6 mu A Ar-16+) and V3 (120 mu A Ar14+, 58 mu A Ar16+). Results are discussed and explained as a consequence of the increase of the ECR zone volume.