Study of beamlets extracted from a multi-aperture and five-stage acceleration system

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

doi:10.1063/5.0080804

Cited by 6 publications

(3 citation statements)

References 33 publications

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“…90% of H − were assumed to start uniformly on the most of emitting surface. Another 10% of H − were launched from the edge of the PG aperture (∼1 mm) with a larger divergence [35]. The space charge effect of the H − beam was considered via a bidirectional particle-field coupling.…”

Section: Problem Analysismentioning

confidence: 99%

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

Yang,

Wei,

et al. 2024

Plasma Phys. Control. Fusion

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The negative ion based neutral beam injection (NNBI) is a desirable plasma heating and current drive method for the large-scale magnetic fusion devices. Due to the strict requirements and difficult development of the negative ion source for fusion, a long-pulse negative ion source has been developed under the framework of the Comprehensive Research Facility for Fusion Technology (CRAFT) in China. This negative ion source consists of a single RF driver plasma source and a three-electrode accelerator. The typical extraction and acceleration voltage are 4~8 kV and 40~50 kV, respectively.During one shot of the long-pulse (~100 s) beam extraction, the gas pressure in the vacuum vessel increased sharply and the temperature of the cryopump rise from 8 K to 20 K. Moreover, the vessel wall appeared a high temperature after several long-pulse shots. A self-consistent simulation of beam-gas interaction revealed that the heat loads on the vessel wall should be caused by the stray electrons ejecting from the accelerator. Those stray electrons are mainly generated via the stripping or ionization collisions and strongly deflected by the downstream side of the deflection magnetic field for the co-extracted electron. The location of hot spots measured by infrared thermography is consistent with the simulation results. To solve this problem, a series of electron dumps are designed to avoid the direct impinging of the ejecting electrons on the cryopump and the vessel wall. And the results suggest that the hot spots are almost eliminated.

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Section: Problem Analysismentioning

confidence: 99%

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

Yang,

Wei,

et al. 2024

Plasma Phys. Control. Fusion

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“…Divergences between 10 and 15 mrad have been observed these in RF-source based experiments, albeit at beam energies below 45 keV [8][9][10]. Divergences below 7 mrad have been measured at arc-source based experiments, mostly at higher beam energies [11][12][13].…”

Section: Introductionmentioning

confidence: 97%

Beam optics of RF ion sources in view of ITER’s NBI systems

den Harder,

Barnes,

Heinemann

et al. 2024

Nucl. Fusion

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A low beamlet divergence is crucial for the efficiency of the ITER-NBI systems, since it affects the transmission of the beam through the duct. There is a requirement of 7 mrad e-folding divergence for the ITER Heating Neutral Beam. Significantly higher divergences (10-15 mrad) have been observed in RF-source based experiments albeit at low beam energy. This could be the consequence of a broad perpendicular velocity distribution of the H-/D- particles before extraction. This paper explores this hypothesis and its implications for ITER. To estimate H-/D- perpendicular temperatures in the RF-driven BATMAN Upgrade test facility, spatially resolved measurements of the beam power density are compared with IBSimu calculations. The estimated perpendicular temperatures show a strong dependence on the source filling pressure, decreasing from approximately 4 eV at 0.3 Pa to 2 eV at 0.4 Pa. Ion-optics calculations of the ITER-HNB grid system are performed to evaluate whether the temperatures estimated in the BATMAN Upgrade test facility are tolerable in view of beam-grid interaction and beamline transmission. The beamline transmission is fairly insensitive to the perpendicular temperature, but the heat loads at the downstream grids increase with the perpendicular temperature.

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“…Filament-arc negative ion sources have been widely investigated and used for Negative ion Neutral Beam Injection (NNBI) systems [1], as opposed to Radio-Frequency (RF) sources, on which the R&D activities have more recently started. Filament sources are capable of delivering high current negative ion beams at 1 MeV energy with 3 mrad divergence, as demonstrated in the Megavolt Test Facility at QST [2]. A minimum divergence of 12 mrad was achieved in the ITER ion source prototype with 42 keV beam energy [3].…”

Section: Introductionmentioning

confidence: 99%

Modelling of plasma discharge in a filament negative ion source

Candeloro,

Sartori,

Kisaki

et al. 2024

J. Phys.: Conf. Ser.

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Most of the currently operating Negative ion Neutral Beam Injectors (N-NBIs) exploit filament powered sources for the generation of beam ions. Being widely used in fusion experiments, the filament arc technology has been thoroughly investigated and optimized over the years, allowing to achieve excellent performances in terms of extracted beam optics. The source geometry, the magnetic field topology and the arc power strongly influence both the plasma discharge and the background gas properties and, consequently, the beam features. In this framework, this contribution describes a numerical investigation of the plasma properties in a filament-powered negative ion source, performed by means of a 2D3V Particle In Cell-Monte Carlo Collisions (PIC-MCC) code. Specifically, we discuss plasma formation by the thermionic electrons emitted by the filaments, investigating their interaction with the background gas. We also study the plasma diffusion through the magnetic filter field and how the latter modifies plasma density, electron temperature and plasma potential along the axial direction when approaching the plasma facing electrode.

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Study of beamlets extracted from a multi-aperture and five-stage acceleration system

Cited by 6 publications

References 33 publications

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

Beam optics of RF ion sources in view of ITER’s NBI systems

Modelling of plasma discharge in a filament negative ion source

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