Physical Performance Analysis And The Progress Of The Development Of The Negative Ion RF Source For The ITER NBI System

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.