The development of a large-area RF source for negative hydrogen ions, an official EFDA task agreement, is aiming at demonstrating ITER-relevant ion source parameters. This implies a current density of 20 mA/cm 2 accelerated Dions at a source filling pressure of ≤ 0.3 Pa and an electron to ion ratio of ≤ 1 from a PINI-size extraction area for pulse lengths of up to 1 hour. The work is progressing along three lines in parallel: (i) optimisation of current densities at low pressure and electron/ion ratio, utilising small extraction areas (< 100 cm 2) and short pulses (< 10 s); (ii); investigation of extended extraction areas (< 300 cm 2) and pulse lengths of up to 3600 s; (iii) investigation of a size-scaling on a half-size ITER plasma source. Three different testbeds are being used to carry out those investigations in parallel. An extensive diagnostic and modelling programme accompanies the activities. The paper contains the recent achievements and the status of preparations in those four areas of development

Development of negative hydrogen ion sources for neutral beam systems is closely linked with an optimisation of negative ion formation in hydrogen plasmas which requires knowledge of the plasma parameters. Emission spectroscopy is introduced as a non-invasive and in-situ diagnostic tool for line of sight averaged plasma parameters. Diagnostic lines and simplified analysis methods for a variety of plasma parameters, such as electron density and electron temperature, gas temperature, atomic and molecular hydrogen density as well as cesium densities (atoms and ions) and negative ion densities are identified and prepared for direct application. Emphasis is laid on results obtained in RF generated negative ion sources. Correlations of plasma parameters with extracted negative ion current densities are discussed. Stripping losses in the extraction system are quantified by using beam emission spectroscopy.

Wendelstein 7-AS was the first modular stellarator device to test some basic elements of stellarator optimization: a reduced Shafranov shift and improved stability properties resulted in β-values up to 3.4% (at 0.9 T). This operational limit was determined by power balance and impurity radiation without noticeable degradation of stability or a violent collapse. The partial reduction of neoclassical transport could be verified in agreement with calculations indicating the feasibility of the concept of drift optimization. A full neoclassical optimization, in particular a minimization of the bootstrap current was beyond the scope of this project. A variety of non-ohmic heating and current drive scenarios by ICRH, NBI and in particular, ECRH were tested and compared

Abstract. For heating and current drive the neutral beam injection system for ITER requires a 1 MeV deuterium beam for up to 1 h pulse length. In order to inject the required 17 MW the large area source (1.9m x 0.9m) has to deliver 40 A of negative ion current at the specified source pressure of 0.3 Pa. In 2007 the IPP RF driven negative hydrogen ion source was chosen as the new reference source for the ITER NBI. Although the IPP RF source has made substantial progress towards ITER's requirements in the last years there are still open issues to be addressed. Apart from the homogeneity of such a large RF source and the long pulse stability, a very critical factor is the amount of co-extracted electrons limiting also the maximum achievable ion current density. For all these issues, the control of the plasma chemistry and the processes in the boundary layer in the source are the most critical item as cesium evaporation is needed for the production of negative hydrogen ions in sufficient quantities. The development efforts at the IPP test facilities are now focused on the achievement of stable long pulses at the test facility MANITU and on demonstration of a sufficiently homogeneous large cesiated RF plasma operation at the large ion source test facility RADI. MANITU is operating now routinely at stable pulses of up to 10 min with parameters near the ITER requirements; RADI demonstrated that a pure deuterium plasma is sufficiently uniform. Overall objectives are to identify tools for control of the source performance. The performance analysis is strongly supported by an extensive diagnostic program and modelling of the source and beam extraction. As an intermediate step between the MANITU and the NBTF RF source, IPP is presently designing the new test facility ELISE for long pulse plasma operation and short pulse, but large-scale extraction from a half-size ITER source; commissioning is planned for 2010.