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

Boeuf, Jean-Pierre; Fubiani, G.; Garrigues, Laurent

doi:10.1088/1361-6595/aa68c9

Cited by 2 publications

(2 citation statements)

References 4 publications

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“…In fully kinetic models, the associated space charge is coupled to the electric field to produce self-consistent field effects via a numerical solution to Poisson's equation. The Debye length at the anticipated plasma densities must be resolved to avoid numerical heating of the electrons, see [8] and section 3 in [9], augmented by [10]. At high plasma density the Debye length can be smaller than a micron, much smaller than any gradients that may be observed at the same spatial location.…”

Section: Introductionmentioning

confidence: 99%

Practical considerations for modeling streamer discharges in air with radiation transport

Stephens

Abide

Fierro

et al. 2018

Plasma Sources Sci. Technol.

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Two basic challenges limiting the simulation capabilities of the streamer discharge community are the efficient resolution of Poisson's equation and the proper treatment of photoionization. This paper addresses both of these challenges, beginning with a graphics processing unit executed multigrid (MG) algorithm to efficiently solve Poisson's equation on a massively parallel platform. When utilized in a 3D particle-in-cell (PIC) model with radiation transport, the MG solver is demonstrated to reduce the required simulation time by approximately a factor of three over a conventional Jacobi scheme. Next, a fully theoretical photoionization model, based on the basic properties of N 2 and O 2 molecules is developed as an alternative to widely utilized semi-empirical models. Following a review of N 2 emission properties, a total of eight transitions from only three excited states are reported as a base set of transitions for a practical physicsbased photoionization model. A 3D PIC simulation of streamer formation is demonstrated with two dominant transitions included in the radiation transport model.

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Section: Introductionmentioning

confidence: 99%

Practical considerations for modeling streamer discharges in air with radiation transport

Stephens

Abide

Fierro

et al. 2018

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

Cited by 2 publications

References 4 publications

Practical considerations for modeling streamer discharges in air with radiation transport

Practical considerations for modeling streamer discharges in air with radiation transport

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

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