Modeling the particle transport and ion production in a RF driven negative hydrogen ion source for ITER NBI

Wünderlich, D.; McNeely, P.; Schiesko, L.; Fantz, U.; Franzen, P.; NNBI-Team,

doi:10.1063/1.4792765

Cited by 6 publications

(3 citation statements)

References 21 publications

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“…Typical applications are sources for accelerator systems [19][20][21] and NBI systems at fusion devices [22,23]; the latter using high power arc sources. In the case of RF-driven sources the negative ions are produced at the plasma grid surface near the extraction apertures by a conversion of mainly neutral hydrogen atoms [24,25]. The necessary low work function of the plasma grid surface is achieved by evaporating caesium onto that surface [14,26,27].…”

Section: Introductionmentioning

confidence: 99%

Progress of the ELISE test facility: results of caesium operation with low RF power

et al. 2015

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The ion source of the ELISE test facility (0.9×1.0 m 2 with an extraction area of 0.1 m 2) has half the size of the ion source foreseen for the ITER NBI beam lines. Aim of ELISE is to demonstrate that such large RF driven negative ion sources can achieve the following parameters at a filling pressure of 0.3 Pa and for pulse lengths of up to one hour: extracted current densities of 28.5 mA/cm 2 in deuterium and 33.0 mA/cm 2 in hydrogen, a ratio of co-extracted electrons to extracted ions below one and deviations in the uniformity of the extracted beam of less than 10 %. From the results obtained at ELISE so far it can be deduced that for demonstrating the ITER parameters, an RF power of 80 kW/driver will be necessary, i.e. final aim is to demonstrate long pulses (up to one hour) at this power level and a stable source performance. The most crucial factor limiting the source performance during such pulses-in particular in deuterium-is a steady increase in the co-extracted electron current. This paper reports measures that counteract this steady increase, namely applying a dedicated long pulse caesium conditioning technique and modifying the filter field topology by adding strengthening external permanent magnets. Additionally, RF issues are discussed that prevented increasing the RF power towards the target value. Although it was not possible up to now to perform long pulses at 80 kW/driver, a significant improvement of the source performance and its stability are demonstrated. The latter allowed performing the very first 1 h deuterium pulse in ELISE.

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Section: Introductionmentioning

confidence: 99%

Progress of the ELISE test facility: results of caesium operation with low RF power

et al. 2015

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“…In order to achieve the ITER-relevant negative hydrogen ion currents, the use of the surface H − production process is presently mandatory: here the negative ions are produced at the PG surface near the extraction apertures by a conversion of mainly neutral hydrogen atoms [22,23]. The necessary low work function of the PG surface is achieved by evaporating caesium onto that surface [12][13][14].…”

Section: Introductionmentioning

confidence: 99%

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

Franzen

Wünderlich

Fantz

2014

Plasma Phys. Control. Fusion

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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.

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“…The generation of negative ions in the RF negative ion source primarily occurs through the surface process of neutral atoms on the plasma grid near the extraction hole [15][16][17][18] . In current NBI systems, this process is achieved by evaporating cesium onto the surface of the PG [19][20][21][22]. A magnetic filter field needs to be installed in front of the PG to reduce the electron temperature in this region and the extracted electron current.…”

Section: Experiments Facilitymentioning

confidence: 99%

Preliminary experimental research on RF coupling efficiency of CRAFT NNBI prototype ion source

Wang,

Liu,

Wei

et al. 2023

Phys. Scr.

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A radio frequency inductively coupled plasma source was chose as the prototype ion source for CRFAT NNBI system. The RF coupling efficiency of this negative ion(H−) source is researched by experiment. The effect of the RF ion source’s multi-cusp confinement magnet on the RF coupling efficiency is focused on. It is found that the RF ion source, equipped with a linear type cusp magnet array on the expansion chamber walls, exhibits a higher efficiency of 2% to 6.6% compared to the checkerboard type. Furthermore, the RF coupling efficiency improves by approximately 9% when a confinement magnet is used, as opposed to not having one. The variations in bias voltage have no impact on the RF coupling efficiency. Nonetheless, variations in the magnetic field within the driver region caused by changes in the PG current induce an impact on the plasma in that region. When the PG current was raised from 800 A to 2500 A, it led to a minor reduction in RF coupling efficiency of approximately 2%.

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Modeling the particle transport and ion production in a RF driven negative hydrogen ion source for ITER NBI

Cited by 6 publications

References 21 publications

Progress of the ELISE test facility: results of caesium operation with low RF power

Progress of the ELISE test facility: results of caesium operation with low RF power

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

Preliminary experimental research on RF coupling efficiency of CRAFT NNBI prototype ion source

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