RADI—A RF source size-scaling experiment towards the ITER neutral beam negative ion source

Wünderlich

Plasma Phys. Control. Fusion

2014

Abstract. The test facility ELISE, equipped with a large RF driven ion source (1x0.9 m 2 ) of half the size of the ion source for the ITER neutral beam injection (NBI) system, was constructed in the last three years at the Max-Planck-Institut für Plasmaphysik (IPP), Garching, and is now operational. First measurements of the dependence of the co-extracted electron currents on various operational parameters have been performed. ELISE has the unique feature, that the electron currents can be measured individually on both extraction grid segments, leading to some vertical spatial resolution.Although done in volume operation, where the negative hydrogen ions are created in the plasma volume solely, the results are very encouraging for the operation with cesium, the latter being necessary in order to achieve the relevant negative ions currents for the ITER NBI injectors. The amount of co-extracted electrons could be suppressed sufficiently with moderate magnetic filter fields and by plasma grid bias. Furthermore, the electron extraction is more or less decoupled from the main plasma, as the observed vertical asymmetry of electron extraction is not correlated at all with the plasma asymmetry, which is anyway rather small. Both effects are superior to the experience from the small IPP prototype source; the reason for these encouraging results are most probably the larger size of the source as well as the new geometry of the source having unbiased areas in the centre of the source. The reasons, however, for the observed asymmetry of the extracted electron currents and their dependencies on various operational parameters are not well understood.

Section: The Elise Experimentsmentioning

confidence: 99%

On the electron extraction in a large RF-driven negative hydrogen ion source for the ITER NBI system

Wünderlich

Plasma Phys. Control. Fusion

2014

“…Such a plasma source of roughly half the size of the ITER source with four drivers but no ion extraction is being operated at the RADI test facility [16]. A "dummy plasma grid" of this source allows simulating the vacuum conductance of a grid system.…”

Section: Radi Operationmentioning

confidence: 99%

Development of a RF-driven ion source for the ITER NBI system

Staebler

Fusion Engineering and Design

et al. 2009

Self Cite

Extensive R&D work on RF-driven negative hydrogen ion sources carried out at IPP Garching led to the decision of ITER to select this type of source as the new reference source for the ITER NBI system. The principle suitability of the RF source has been demonstrated in a small scale, short pulse length experiment: accelerated current densities, co-extracted electron currents at a source operation pressure, all well inside the range of the ITER requirements have been achieved simultaneously. In subsequent experiments, pulse lengths up to 1 h and the possibility of modularly extending the source to ITER source dimensions were demonstrated. The results achieved at the various IPP test beds, the lessons learnt during optimising the source for negative ion production and extraction as well as the problems still to be solved are summarized. As the next step in support of the NBI development for ITER, IPP plans to build a new test facility for beam extraction from a source of half the size for ITER.

“…This is done at the two other test facilities MANITU (Multi Ampere Negative Ion Test Unit) where the extraction area is about 200 cm 2 and the pulse length up to 3600 s, using the same source as it is used at BATMAN, and at the dedicated plasma source test facility RADI, which is equipped with a "half-size" source having the full width and half the height of the ITER source. RADI has no extraction and is devoted to demonstrate the modular concept of the RF source and the plasma uniformity of a large RF source [6]. MANITU was upgraded to cw operation by an active cooling of all parts of the source and has achieved now stable one hour pulses; the parameters however, are still below the ITER requirements [7].…”

Section: Status Of the Developmentmentioning

confidence: 99%

The IPP RF Source: A High Power, Low Pressure Negative Ion Source For The Neutral Beam Injection System Of ITER

AIP Conference Proceedings

Kraus

et al. 2008

Self Cite

Abstract. IPP Garching has successfully developed a RF driven negative ion source for the ITER neutral beam injection system. The RF source was chosen recently as the reference source for ITER 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 less than 1 for a small extraction area (7.0x10 -3 m 2 ) and short pulses (< 4 s). The development concentrates now on extending the pulse length and extending the size of the source on two dedicated test facilities. The pulse length can be extended up to one hour at the long pulse test facility having an extraction area of 0.02 m 2 . The large source test facility is equipped a large RF source with the width and half the height of the ITER beam source in order to demonstrate the homogeneity of a large RF plasma. The paper will give a short overview on the results achieved at the three test facilities of IPP; the underlying physical mechanisms are discussed with an emphasis on electron suppression.