Effect of basic physical parameters to control plasma meniscus and beam halo formation in negative ion sources

Miyamoto, K.; Okuda, S.; Nishioka, S.; Hatayama, A.

doi:10.1063/1.4820571

Cited by 22 publications

(23 citation statements)

References 23 publications

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“…In the past, different numerical models [13] [17] for simulating the plasma behavior and negative ion extraction from different RF sources were developed and exploited. However, a direct cross-checked analysis with experimental results using the same input plasma parameters, source conditions and 3D source geometry was not performed yet.…”

Section: Introductionmentioning

confidence: 99%

Comparison of ONIX simulation results with experimental data from the BATMAN testbed for the study of negative ion extraction

et al. 2016

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The development of negative ion (NI) sources for the ITER neutral beam injector is strongly accompanied by modelling activities. The ONIX (Orsay Negative Ion eXtraction) code simulates the formation and extraction of negative hydrogen ions and co-extracted electrons produced in caesiated sources. The 3D geometry of the BATMAN extraction system and the source characteristics such as the extraction and bias potential, 3D magnetic field were integrated in the model. Calculations were performed using plasma parameters experimentally obtained on BATMAN. Comparison of the ONIX calculated extracted NI density with experimental results suggests that predictive calculations of the extraction of negative ions are possible. The results show that for an ideal status of the Cs conditioning the extracted hydrogen NI current density could reach about ~30 mAcm -2 at 10 kV and about ~20 mAcm -2 at 5 kV extraction potential with an electron/NI current density ratio of about 1, as measured in the experiments under the same plasma and source conditions. The dependency of the extracted NI current on the negative ion density in the bulk plasma region from both the modeling and the experiment was investigated. The separate distributions composing the negative ion beam originating from the plasma bulk region and the PG surface are presented for different NI plasma volume densities and NI emission rates from the plasma grid wall respectively. The extracted current from NI produced at the Cs covered plasma grid (PG) surface, initially moving towards the bulk plasma and then being bent towards the extraction surfaces is lower compared to the extracted NI current from directly extracted surface produced ions.

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Section: Introductionmentioning

confidence: 99%

Comparison of ONIX simulation results with experimental data from the BATMAN testbed for the study of negative ion extraction

et al. 2016

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“…It was demonstrated, that electrons are not only pushed back, but also very effectively lost parallel to the field lines towards the side walls of the ion source. Among various physical parameters, the electron loss time parallel to the magnetic field line (τ ∥ ) is one of the key parameters for this process [101,102]. For a sufficiently low value of τ ∥ , the electron density in the plasma is strongly reduced (by more than order of magnitude) and an ion-ion plasma forms [47,48,103,104].…”

Section: Transport Of Charged Particles Through the Magnetic Filtermentioning

confidence: 99%

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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“…[3,4,8]. The trajectories of the charged particles (electrons, H + ions, and H − ions) are solved by the equation of motion where, m, v, q, E and B are mass, velocity, electric charge, local electric field and magnetic field, respectively.…”

Section: Numerical Modelmentioning

confidence: 99%

“…Especially, beam halo can contribute to the heat loads even at the optimum perveance for the beam core [1,2]. Studies using the 2D3V-PIC (two dimension in real space and three dimension in velocity space)·(Particle In Cell), and 3D3V-PIC (three dimension in real space and three dimension in velocity space) model have been done, aiming to understand the extraction mechanisms of H − ions from the negative ion source, [3,4,5]. However, the extraction mechanisms have not been completely clarified yet.…”

Section: Introductionmentioning

confidence: 99%

Study of the negative ion extraction mechanism from a double-ion plasma in negative ion sources

Goto

Miyamoto

Nishioka

et al. 2015

AIP Conference Proceedings

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Study of ion-ion plasma formation in negative ion sources by a three-dimensional in real space and three-dimensional in velocity space particle in cell model Journal of Applied Physics 119, 023302 (2016) Abstract. We have developed a 2D3V-PIC model of the extraction region, aiming to clarify the basic extraction mechanism of H − ions from the double-ion plasma in H − negative ion sources. The result shows the same tendency of the H − ion density n H − as that observed in the experiments, i.e., n H − in the upstream region away from the plasma meniscus (H − emitting surface) has been reduced by applying the extraction voltage. At the same time, relatively slow temporal oscillation of the electric potential compared with the electron plasma frequency has been observed in the extraction region. Results of the systematic study using a 1D3V-PIC model with the uniform magnetic field confirm the result that the electrostatic oscillation is identified to be lower hybrid wave. The effect of this oscillation on the H − transport will be studied in the future.

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Effect of basic physical parameters to control plasma meniscus and beam halo formation in negative ion sources

Cited by 22 publications

References 23 publications

Comparison of ONIX simulation results with experimental data from the BATMAN testbed for the study of negative ion extraction

Comparison of ONIX simulation results with experimental data from the BATMAN testbed for the study of negative ion extraction

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

Study of the negative ion extraction mechanism from a double-ion plasma in negative ion sources

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