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

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.

For heating and current drive the neutral beam injection system for ITER requires a deuterium beam with an energy of 1 MeV for up to 1 h. In order to inject the required 17 MW the ion source has to deliver 40 A of negative ion current. For an accelerated current density of 200 A m −2 at the specified source pressure of 0.3 Pa the extraction area is 0.2 m 2 resulting in a large area source of 1.5 × 0.6 m 2 . Two types of sources have been under discussion, the filamented arc source and the inductively driven RF source, the latter now having been chosen for the ITER reference design. The development of negative ion RF sources, which fulfil these specifications is being carried out at the Max-Planck-Institut für Plasmaphysik at three test facilities in parallel. The required current densities at the ITER relevant pressure have been achieved and even exceeded in a test facility equipped with a small ion source (extraction area of 0.007 m 2 ) at limited pulse length (<4 s). The extraction area can be extended up to 0.03 m 2 and the pulse length up to 3600 s at a second test facility which is dedicated to long pulse operation experiments where pulses up to 800 s have already been achieved. The ion source at the third test facility has roughly the full width and half the height of the ITER source but is not equipped with an extraction system. The aim is to demonstrate the size scaling and plasma homogeneity of RF ion sources. First results from different diagnostic techniques (optical emission spectroscopy and Langmuir probe) are very promising.

Abstract. IPP Garching has successfully developed a RF driven negative ion source for the ITER neutral beam injection system. The RF source is now an interesting alternative to the reference design with filamented sources due to its in principle maintenance-free operation. Current densities of 330 A/m 2 and 230 A/m 2 have been achieved for hydrogen and deuterium, respectively, at a pressure of 0.3 Pa and an electron/ion ratio of 1 for a small extraction area (7.0x10 -3 m 2 ) and short pulses (< 4 s). Reliable deuterium operation with more than 150 pulses in the required parameter range was obtained by an improved cesium operation utilizing a control of all source temperatures (grid as well as source body) and monitoring the amount of cesium in the source. The development concentrates now on extending the pulse length to up to 1 hour and extending the size of the source. The long pulse test bed went into operation last year; pulses of up to some 100 seconds with more or less stable conditions in terms of extracted currents and Cs dynamics have been achieved with current densities in the range of 150 -200 A/m 2 in hydrogen operation. The pulse length, however, is still limited by non-sufficient cooling of some parts of the source and the RF circuit. The commissioning of the so-called "half-size" source test facility started recently with the first plasma pulses; this large RF source with the width and half the height of the ITER NNBI source is dedicated to the demonstration of the homogeneity of a large RF plasma -extraction is foreseen in a latter phase -and the tests of an ITER-relevant RF circuit.