Optics of the NIFS negative ion source test stand by infrared calorimetry and numerical modelling

Veltri, P.; Antoni, V.; Agostinetti, P.; Brombin, M.; Ikeda, K.; Kisaki, M.; Nakano, H.; Sartori, E.; Serianni, G.; Takeiri, Y.; Tsumori, K.

doi:10.1063/1.4932982

Cited by 12 publications

(6 citation statements)

References 6 publications

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“…Similar values are also reached at SPIDER [5]. This divergence is signicantly larger than the divergences typically achieved in lament-arc driven ion sources, albeit often at higher total beam energy [21,22]. A strong reduction of the divergence occurs for higher lling pressure: already a 20% reduction can be achieved at 0.4 Pa lling pressure.…”

Section: Beam Divergence Of Rf H − Sourcessupporting

confidence: 68%

Beam divergence of RF negative hydrogen ion sources for fusion

Wimmer,

Barnes,

den Harder

et al. 2024

J. Phys.: Conf. Ser.

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Neutral beam injectors (NBI) for fusion facilities have strict requirements on the beam divergence (7 mrad for the ITER NBI at 1 MeV). Measurements of the single beamlet divergence of RF negative ion sources (at lower beam energy < 100 keV) show significantly higher values (9–15 mrad), also larger than filament arc sources at similar beam energies. This opened up questions whether the higher divergence is caused by different measurement or evaluation techniques, whether it is a direct cause of the RF source, e.g. due to a higher temperature of negative ions or an oscillating extraction meniscus, and whether it is a problem at all after full acceleration. In a joint effort between the labs modeling and diagnostic capabilities at the NNBI test facilities have been strongly extended and evaluation methods benchmarked. Particularly challenging is the strong increase in beamlet divergence at a lower filling pressure, seen both in filament arc and RF sources. Beside the source and beam investigations carried out in SPIDER (with selected, isolated apertures rather than the total of 1280 apertures) at Consorzio RFX, the IPP test facilities ELISE (640 apertures) and BATMAN Upgrade (70 apertures) contribute to the physics understanding of the beam optics in RF sources. The determination of the beam divergence is not straight-forward because effects originating from measuring the divergence of multiple beamlets (Beam Emission Spectroscopy) and/or constraints from the individual diagnostic (lateral heat conductance in CFC tiles) lead to difficulties. Still, the divergence requirement is not met at the limited total beam energy available at ELISE and BATMAN Upgrade (< 60kV). However, variation of the beam energy show a decrease of the divergence for higher energies and beam simulation for the ITER NBI accelerator predict that the divergence requirement will be met after full acceleration of the negative ion beam.

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Section: Beam Divergence Of Rf H − Sourcessupporting

confidence: 68%

Beam divergence of RF negative hydrogen ion sources for fusion

Wimmer,

Barnes,

den Harder

et al. 2024

J. Phys.: Conf. Ser.

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“…However, in RF negative ion sources the beam divergence is not still foreseen to meet the requirement for ITER-NBI [4,5], where the target value is less than 7 mrad [1]. Only filament-arc-type negative ion sources have achieved to generate such a low divergence beam in a wide energy range from 50 keV to 350 keV [6][7][8][9], which implies that the divergence does not change so much with the beam energy in electrostatic accelerators used for NBIs. Hence, a detailed analysis of the beam properties in the arc-type negative ion sources gives an insight into further improvement of negative ion sources regardless of discharge systems.…”

Section: Introductionmentioning

confidence: 99%

Nonuniform plasma meniscus modelling based on backward calculation of negative ion beamlet

et al. 2022

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The shape of a plasma meniscus is a key factor to determine the beam focusing. The physics model of the meniscus formation for hydrogen negative ion sources has not been established yet. A backward trajectory calculation based on experimental observation is performed in order to derive the particle information at the meniscus. It is observed that the negative ion density is spatially nonuniform in the direction parallel to the magnets for suppression of co-extracted electrons. A nonuniformity of the negative ion density in the vicinity of the meniscus is taken into account in the forward trajectory calculation. It reveals that the nonuniform negative ion distribution leads to degradation of the beam focusing and the beam splitting in phase space. The importance of the spatial distribution of negative ions on meniscus modelling is discussed with a comparison to uniform extraction model.

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“…These approximations have sufficed to achieve the stability of numerical trends and the reproducibility of results. Moreover, benchmarking of acceleration and transport codes with real experiments has shown, in general, a satisfactory overall agreement with the measurements performed in existing negative ion accelerators [13][14][15], motivating their extensive employment in the design phase of the future neutral beam injectors (NBIs) of fusion experiments such as ITER and DEMO.…”

Section: Introductionmentioning

confidence: 75%