Comment on ‘Issues in the understanding of negative ion extraction for fusion’

Mochalskyy, S.; Minea, Tiberiu; Revel, A.; Montellano, I. M.; Wünderlich, D.; Fantz, U.

doi:10.1088/1361-6595/aa68d0

Cited by 3 publications

(5 citation statements)

References 20 publications

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“…This was shown in our first paper [2] in the context of negative ion extraction and was more systematically illustrated in our following papers [3,4]. This point is well known by the plasma simulation community and it is surprising that the authors of the comment and of the criticized papers (see [1] and references therein) used mesh sizes much larger than the Debye length, their argument being that the number of mesh points must be limited in order to carry out 3D simulations. Moreover the method of injection of the plasma particles in the simulation domain was not correct in these papers, as shown in [2,3], and led to non-physical results.…”

mentioning

confidence: 70%

“…-We showed that inappropriate choice of mesh size in the PIC simulations can lead to erroneous conclusions. In the simulation results of the authors of the comment (see [1] and references therein), it appears that negative ions are not extracted from a quasineutral plasma behind a meniscus, but rather from the tips of the chamfered grid apertures where the electric field was sufficiently large to directly (i.e. without space charge neutralization) extract a large negative ion current density from the cesiated surface.…”

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confidence: 99%

“…The authors of the comment [1] list specific and detailed points related to our criticism of their published work on the simulation of negative ion extraction. They claim that their simulations results are in agreement with experiments whereas we showed in our initial paper that their results and their conclusions are wrong because of misuse of the particlein-cell Monte Carlo collision (PIC MCC) simulations.…”

mentioning

confidence: 99%

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Reply to Comment on ‘Issues in the understanding of negative ion extraction for fusion’

Boeuf

Fubiani

Garrigues

2017

Plasma Sources Sci. Technol.

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confidence: 70%

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confidence: 99%

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confidence: 99%

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Reply to Comment on ‘Issues in the understanding of negative ion extraction for fusion’

Boeuf

Fubiani

Garrigues

2017

Plasma Sources Sci. Technol.

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“…No numerical convergence analysis had been performed in these studies. As a consequence, this triggered a debate in the negative ion extraction modeling community regarding whether or not one must strictly respect the numerical constraints of explicit PIC schemes 140,141 .…”

Section: Extraction Of Negative Ionsmentioning

confidence: 99%

Tutorial: Modeling of the extraction and acceleration of negative ions from plasma sources using particle-based methods

Garrigues

Fubiani

2023

Journal of Applied Physics

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In this Tutorial, we consider plasma sources with applications to fusion devices and high energy accelerators. These ion sources typically produce negative ions from hydrogen-isotope gases, which are extracted through one or multiple apertures and accelerated to high kinetic energies. Next, they are either double stripped of two electrons to form positive ions used as precursors in accelerator devices or neutralized to produce a neutral beam injected in tokamak reactors. Contrary to the working conditions of most ion sources where volume production prevails, the mechanism of negative ion production by dissociative electron attachment on vibrationally excited molecules inside the plasma volume of fusion-type hydrogen-fueled high power discharges is mostly balanced by their destruction by detachment before being extracted rendering this means of producing negative ions rather inefficient. Surface production through the transfer of electrons from low work function metallic materials to the impacting atoms is the alternative solution to fulfill the requirements for the applications concerned. Negative ions are produced close to the aperture from which they are extracted. As a result, the analysis and understanding of the extraction mechanisms through experimental diagnostics is rather difficult due to the lack of accessibility and can only give a partial view. In addition, most of the experimental work is focused on the validation of requirements for the applications and not to the investigation of the fundamental processes that take place inside these types of sources. This Tutorial is focused on the description and understanding of the physical mechanisms behind the extraction and acceleration of negative ions from hydrogen plasma sources through modeling methods. We describe the numerical techniques of particle-based methods with a specific emphasis on particle-in-cell Monte Carlo collision algorithms. An analysis of the physical processes involved in driving the negative ions from the plasma source, across the apertures and inside the accelerator as reported in the literature, is presented in detail. This Tutorial concludes with additional and future works to be addressed in the coming years.

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“…The topological structure of the magnetic field, especially the magnetic deflection field in EG, plays an important role in the numerical results. Small changes in magnetic field intensity or topological structure can greatly change the extracted electron current, and the correlation of simulation results can only be proposed based on a correctly established magnetic field structure [14].…”

Section: Open Access Edited Bymentioning

confidence: 99%

Three-dimensional simulation of electron extraction process and optimization of magnetic field based on multi-aperture structure of negative hydrogen ion source

Xie

Liu²,

Liu³

2023

Front. Phys.

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In most of the simulations of the extraction region of negative hydrogen ion sources, the single-aperture simulation is often adopted by researchers to study the plasma phenomenon due to its small simulation domain and short calculation time. However, due to the complex three-dimensional magnetic field structure in the extraction region of the negative hydrogen ion source, the single aperture often does not meet the periodicity. In this paper, the complex three-dimensional magnetic field topology is established. The magnetic field includes the magnetic filter field and the magnetic deflection field. The influence of the plasma sheath is taken into account. The electron extraction process in the multi-aperture structure of the extraction region of a negative hydrogen ion source is numerically calculated using the PIC method. Besides, the magnetic field structure is optimized. Ultimately, the electron beam uniformity near the plasma grid is improved effectively, which has certain guiding significance for engineering application.

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Comment on ‘Issues in the understanding of negative ion extraction for fusion’

Cited by 3 publications

References 20 publications

Reply to Comment on ‘Issues in the understanding of negative ion extraction for fusion’

Reply to Comment on ‘Issues in the understanding of negative ion extraction for fusion’

Tutorial: Modeling of the extraction and acceleration of negative ions from plasma sources using particle-based methods

Three-dimensional simulation of electron extraction process and optimization of magnetic field based on multi-aperture structure of negative hydrogen ion source

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