Performance of multi-aperture grid extraction systems for an ITER-relevant RF-driven negative hydrogen ion source

<jats:p>The ITER neutral beam system requires a negative hydrogen ion beam of 48 A with an energy of 0.87 MeV, and a negative deuterium beam of 40 A with an energy of 1 MeV. The beam is extracted from a large ion source of dimension 1.9 × 0.9 m<jats:sup>2</jats:sup> by an acceleration system consisting of seven grids with 1280 apertures each. Currently, apertures with a diameter of 14 mm in the first grid are foreseen.</jats:p> <jats:p>In 2007, the IPP RF source was chosen as the ITER reference source due to its reduced maintenance compared with arc-driven sources and the successful development at the BATMAN test facility of being equipped with the small IPP prototype RF source ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="nf372069in001.gif" /> of the area of the ITER NBI source). These results, however, were obtained with an extraction system with 8 mm diameter apertures.</jats:p> <jats:p>This paper reports on the comparison of the source performance at BATMAN of an ITER-relevant extraction system equipped with chamfered apertures with a 14 mm diameter and 8 mm diameter aperture extraction system. The most important result is that there is almost no difference in the achieved current density—being consistent with ion trajectory calculations—and the amount of co-extracted electrons. Furthermore, some aspects of the beam optics of both extraction systems are discussed.</jats:p>