A new version of the high efficiency source is being developed for the European Spallation Source. The goal of these experiments is to produce 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 into two parts of different plasma parameters by means of a filter magnetic field. Furthermore, the plasma chamber is aligned unsymmetrically with respect to the z axis of the extractor. We obtained a current density of 10 mA/cm(2) for an are power as small as 1 kW. In preliminary experiments, a beam of 10 mA was extracted-at an extraction voltage of 8 kV (1.8 impurities). Measurements of the beam current density, electron to H- ratio, and the ion composition for a wide range of discharge conditions will be presented in this article. (C) 1996 American Institute of Physics. References: 3
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