Reverse trajectory analysis of the hydrogen negative ion beam in a prototype accelerator for ITER

Kisaki, M.; Kojima, Akira; Saquilayan, G. Q.; Hoshino, Junichi; Ichikawa, Masahiro; Shimabukuro, Yuji; Murayama, Masamichi; Watanabe, K.; Tobari, H.; Kashiwagi, M.

doi:10.1088/1742-6596/2244/1/012061

Cited by 4 publications

(4 citation statements)

References 8 publications

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“…The current density is found to be peaked in the side annulus of the aperture and unbalanced in the horizontal direction (the one perpendicular to the local magnetic field due to EDM). Such results are in agreement with those of backward-tracing models applied to emittance measurement performed at QST (Japan) [35,36]. As it can be noticed, the high transverse velocity tails highlighted in figure 12 mainly correspond to convergent particles, populating the odd quadrants of the emittance plot (see figure 13(b)).…”

Section: Surface Conversion Of Neutralssupporting

confidence: 86%

Influence of positive ions on the beamlet optics for negative-ion neutral beam injectors

Pimazzoni

Sartori²,

Serianni³

et al. 2023

Nucl. Fusion

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Neutral beam injectors (NBIs) are based on the neutralization of ion beams accelerated at the desired energy. In the case of the ITER heating and diagnostic neutral beams (HNB and DNB), the target heating power translates into stringent requirements on the acceptable beamlet divergence and aiming, to allow the beam reaching the fusion plasma. The beamlets composing the accelerated beam are experimentally found to feature a transverse velocity distribution exhibiting two Gaussian components: the well-focused one is referred to as core component while the rest of the beam, the halo, describes beam particles with much worse optics. The codes which simulate beam extraction and acceleration usually assume that the negative ions move towards the plasma meniscus with a laminar flow (no transverse velocity) or that the transverse velocity distribution can be modelled as a Maxwellian and that the current density is uniformly illuminating the meniscus; under such approximations, the presence of highly divergent components cannot be explained. In this work, we develop a simple test particle tracing code with Monte Carlo collisions, named ICARO (Ions Coming AROund), to study the negative ion transport in the extraction region and derive the spatial and velocity distribution of the negative ions at the meniscus (i.e. the plasma boundary where a beamlet is extracted). In particular, the origin of the beamlet halo, and its dependence on the source parameters are discussed, highlighting as a key parameter the positive-ion energy distribution in the source plasma.

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Section: Surface Conversion Of Neutralssupporting

confidence: 86%

Influence of positive ions on the beamlet optics for negative-ion neutral beam injectors

Pimazzoni

Sartori²,

Serianni³

et al. 2023

Nucl. Fusion

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“…It is clearly shown that three Gaussian components observed in the phase space measurement originate from the different locations at the meniscus and that the origins of three components are separated horizontally, where the centre component also exists in the region covered with the lower component. The H − ions occupy a narrower region than the PG aperture in vertical direction, which was not observed in the backward calculation for a multistage accelerator [19]. This may be because only single ellipse was observed in the case of the multistage accelerator due to the lower spatial resolution of the emittance meter using one-dimensional carbon-fiber-composite tiles for the detector.…”

Section: Backward Trajectory Calculationmentioning

confidence: 82%

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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“…This beam edge estimation only considers the beam after the ground grid which have exited the accelerator. The overall picture of the beam edge should also include portions of the beam that were directly intercepted on the accelerator grids, measured as part of the grid heat loads [9]. Investigation of the beam periphery is currently in ongoing to determine the susceptible parts of the accelerator and aim to suppress the beam edge which will contribute to extend the operational limit for long beam pulses.…”

Section: Beam Acceleration Under Perveance Matched Condition With Itermentioning

confidence: 99%

High Power Density Beam Measurement of a Single Beamlet Multi-Grid Prototype H^- Negative Ion Accelerator

Saquilayan

Kisaki

Kojima

et al. 2022

J. Phys.: Conf. Ser.

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Beam optics of the ITER prototype accelerator with 88 mm acceleration gap length has been examined through H- beam acceleration tests at the ITER target beam perveance. The beam optics has been examined for beam energies up to 790 keV under the ITER target perveance. The total grid heat load was successfully reduced to 10 %, which was lower than the allowable value of 15 %. The beam emittance of the ITER perveance has been measured for the first time by using newly developed emittance measurement system consisting of carbon-fiber-composite (CFC) plate with pin-holes. The emittance of 790 keV H- beam shows the divergence angle of the beam core is satisfied with the ITER requirement of <7 mrad. Measurement at the beam periphery was made possible by modifying the pin-hole size of pepper-pot apertures, and the observed divergent components were 20 mrad. The ratio of the diverged beam became lower with the increase of the beam energy. This result contributes the design of the ITER accelerator and the beam line components.

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Reverse trajectory analysis of the hydrogen negative ion beam in a prototype accelerator for ITER

Cited by 4 publications

References 8 publications

Influence of positive ions on the beamlet optics for negative-ion neutral beam injectors

Influence of positive ions on the beamlet optics for negative-ion neutral beam injectors

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

High Power Density Beam Measurement of a Single Beamlet Multi-Grid Prototype H^- Negative Ion Accelerator

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Reverse trajectory analysis of the hydrogen negative ion beam in a prototype accelerator for ITER

Cited by 4 publications

References 8 publications

Influence of positive ions on the beamlet optics for negative-ion neutral beam injectors

Influence of positive ions on the beamlet optics for negative-ion neutral beam injectors

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

High Power Density Beam Measurement of a Single Beamlet Multi-Grid Prototype H- Negative Ion Accelerator

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Product

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High Power Density Beam Measurement of a Single Beamlet Multi-Grid Prototype H^- Negative Ion Accelerator