AN H- SOURCE FOR ESS

A new version of the high efficiency source is being developed for the European Spallation Source. The goal of these experiments is to produ ce a nearly pure H- ion beam with a low electron to H- ratio and high current (70 mA). To achieve this, the discharge chamber is divided int o two parts of different plasma parameters by means of a filter magnet ic field. Furthermore, the plasma chamber is aligned unsymmetrically w ith respect to the z axis of the extractor. We obtained a current dens ity of 10 mA/cm(2) for an are power as small as 1 kW. In preliminary e xperiments, a beam of 10 mA was extracted-at an extraction voltage of 8 kV (1.8% impurities). Measurements of the beam current density, elec tron to H- ratio, and the ion composition for a wide range of discharg e conditions will be presented in this article. (C) 1996 American Inst itute of Physics.