Massive parallel 3D PIC simulation of negative ion extraction

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

doi:10.1063/1.5001397

Cited by 19 publications

(22 citation statements)

References 30 publications

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“…For the simplest case of an electropositive hydrogen plasma with one positive ion specie (protons), potential sheath drops and sheath sizes of the presented analytical model were successfully benchmarked in 51 against two particle-in-cell codes ONIX 52,53 and BACON 21 and one analytical model 28 . Both ONIX and BACON enforce the Bohm criterion and the presheath voltage drop within 20 % when compared to fluid sheath results.…”

Section: Comparison Of Analytical and Particle-in-cell Resultsmentioning

confidence: 99%

Kinetic sheath in presence of multiple positive ions, negative ions, and particle wall emission

Schiesko

Wünderlich

Montellano

2020

Journal of Applied Physics

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The region between a Maxwellian plasma source and a floating or current-carrying surface is described by a static, one-dimensional collisionless kinetic sheath model. In the plasma source, electrons, negative ions and several positive ion species with different temperatures can be included. The surface (wall) can emit electrons and/or negative ions. When the flux of surface-emitted negative ions and/or electrons reaches a critical value, the sheath becomes spacecharge saturated which leads to the formation of a virtual cathode in front of the emitting wall and set the maximum current density that can be transported from the surface to the plasma. The analytical results are benchmarked against a particle-in-cell code.

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Section: Comparison Of Analytical and Particle-in-cell Resultsmentioning

confidence: 99%

Kinetic sheath in presence of multiple positive ions, negative ions, and particle wall emission

Schiesko

Wünderlich

Montellano

2020

Journal of Applied Physics

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“…These calculations are again based on a strongly reduced value of the plasma density. The ONIX code [62,63] has been initially developed at LPGP, Université Paris, France and is now being advanced in close cooperation by LPGP and IPP Garching in order to investigate the formation of the meniscus and mechanisms responsible for the co-extraction of electrons from the RF driven prototype source and the ELISE source and the isotope effect hydrogen-deuterium.…”

Section: Particle In Cell Modelling Of Negative Ion Sources For Fusionmentioning

confidence: 99%

“…Most widely used is the re-injection scheme where a positive ion being lost at a wall results in the re-injection of an electron and a positive ion. If a different re-injection scheme is to be used, a critical validation is mandatory in order to avoid non-physical results [54,63]. Using an injection volume and re-injecting lost particles reduces the needed computational time and additionally has the advantage of being relatively easy and intuitive to implement.…”

Section: Numerical Aspectsmentioning

confidence: 99%

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Review of particle-in-cell modeling for the extraction region of large negative hydrogen ion sources for fusion

Wünderlich

Mochalskyy

Montellano

et al. 2018

Review of Scientific Instruments

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Particle-in-cell (PIC) codes are used since the early 1960s for calculating self-consistently the motion of charged particles in plasmas, taking into account external electric and magnetic fields as well as the fields created by the particles itself. Due to the used very small time steps (in the order of the inverse plasma frequency) and mesh size, the computational requirements can be very high and they drastically increase with increasing plasma density and size of the calculation domain. Thus, usually small computational domains and/or reduced dimensionality are used. In the last years, the available central processing unit (CPU) power strongly increased. Together with a massive parallelization of the codes, it is now possible to describe in 3D the extraction of charged particles from a plasma, using calculation domains with an edge length of several centimeters, consisting of one extraction aperture, the plasma in direct vicinity of the aperture, and a part of the extraction system. Large negative hydrogen or deuterium ion sources are essential parts of the neutral beam injection (NBI) system in future fusion devices like the international fusion experiment ITER and the demonstration reactor (DEMO). For ITER NBI RF driven sources with a source area of 0.9 × 1.9 m and 1280 extraction apertures will be used. The extraction of negative ions is accompanied by the co-extraction of electrons which are deflected onto an electron dump. Typically, the maximum negative extracted ion current is limited by the amount and the temporal instability of the co-extracted electrons, especially for operation in deuterium. Different PIC codes are available for the extraction region of large driven negative ion sources for fusion. Additionally, some effort is ongoing in developing codes that describe in a simplified manner (coarser mesh or reduced dimensionality) the plasma of the whole ion source. The presentation first gives a brief overview of the current status of the ion source development for ITER NBI and of the PIC method. Different PIC codes for the extraction region are introduced as well as the coupling to codes describing the whole source (PIC codes or fluid codes). Presented and discussed are different physical and numerical aspects of applying PIC codes to negative hydrogen ion sources for fusion as well as selected code results. The main focus of future calculations will be the meniscus formation and identifying measures for reducing the co-extracted electrons, in particular for deuterium operation. The recent results of the 3D PIC code ONIX (calculation domain: one extraction aperture and its vicinity) for the ITER prototype source (1/8 size of the ITER NBI source) are presented.

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“…In volume production, ions enter the extraction region from the volume of the expansion chamber (laminar flow) and they are influenced by the electron deflection field (around 7 mT at the plasma-facing side of the PG and up to 30 mT at the beam-facing side of the PG) so that their entrance angle into the aperture is horizontally deflected and alternated row by row. In a caesiated source, part of the negative ions is directly extracted from the chamfered surfaces of the plasma side of the PG, as described by the PIC Montecarlo ONIX code for a domain around a single aperture [25]: the influence of the electron deflection field is expected to be smaller for these particles. Some insights could be gained by coupling the ONIX simulations together with the particle tracking beam code BBC-NI [23] for the BES spectra simulation; investigations and modeling are ongoing work but a straightforward and clear explanation is still missing.…”

Section: Beam Features During Cs Conditioningmentioning

confidence: 99%

Uniformity of the large beam of ELISE during Cs conditioning

Bonomo

Mario

Nocentini

et al. 2018

AIP Conference Proceedings

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The ELISE test facility is based on a modular concept design which has been replicated in the ITER Negative Beam Ion (NBI) source with twice the size in the vertical direction. The target of ELISE is to achieve simultaneously the ITER NBI parameters in terms of negative ion extracted current (in H and D), pulse duration and ratio of co-extracted electron to ion below 1 at a source filling pressure of 0.3 Pa. While the source plasma can be operated for 1 h, only 9.5 s of beam extraction every  150 s can be applied, with a maximum total voltage of 60 kV due to limitations of the HV power supply; only divergences larger than 1 deg have been measured so far. The beam in ELISE is investigated by various diagnostics: the currents in the grid system are electrically measured and provide the total extracted negative ion current as well as information on the beam losses separately measured in the top and bottom grid segments of the extraction and grounded grids; the Beam Emission Spectroscopy (BES) gives information on the beam intensity and divergence (vertical and horizontal profiles); Infra-red (IR) analysis of the diagnostic calorimeter provides a 2D map of the beam power density and, consequently, the accelerated current density distribution as well as the total accelerated current. The spatial resolution of the beam diagnostics at ELISE (BES; diagnostic calorimeter) allows to resolve and describe in intensity and divergence the two beam segments associated to the two top and bottom grid segments. Following the evolution of the beam segments during the Cs conditioning process (i.e. Cs evaporation in the source to move from volume production of negative ions to surface production) allows to optimize the Cs conditioning by using the beam as an indirect measurement of the negative ion production. At high source performance and stable conditioning, the vertical beam uniformity in terms of accelerated current can be easily achieved: the difference between top and bottom beam segments is almost always well within the 10%.

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Massive parallel 3D PIC simulation of negative ion extraction

Cited by 19 publications

References 30 publications

Kinetic sheath in presence of multiple positive ions, negative ions, and particle wall emission

Kinetic sheath in presence of multiple positive ions, negative ions, and particle wall emission

Review of particle-in-cell modeling for the extraction region of large negative hydrogen ion sources for fusion

Uniformity of the large beam of ELISE during Cs conditioning

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