Analysis of the H− ion emissive surface in the extraction region of negative ion sources

Kameyama, Naofumi; Fukuyama, Takashi; Wada, S.; Kuppel, Sylvain; Tsumori, K.; Nakano, H.; Hatayama, A.; Miyamoto, K.; Fukano, Azusa; Bacal, M.

doi:10.1063/1.3673495

Cited by 11 publications

(17 citation statements)

References 3 publications

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“…Next, the basically same model has been applied to the NIFS R&D H À ion source experiments with the H À surface production. 14 Again, our model well reproduces the most of the essential features observed in the experimental observations, e.g., the H þ and H À "double ion" plasma formation almost without electrons in front of the PG. 15 On the basis of these careful checks, the model has been applied to the analysis in the present study.…”

Section: Simulation Modelsupporting

confidence: 73%

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

Miyamoto

Okuda

Nishioka

et al. 2013

Journal of Applied Physics

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Our previous study shows that the curvature of the plasma meniscus causes the beam halo in the negative ion sources: the negative ions extracted from the periphery of the meniscus are over-focused in the extractor due to the electrostatic lens effect, and consequently become the beam halo. In this article, the detail physics of the plasma meniscus and beam halo formation is investigated with two-dimensional particle-in-cell simulation. It is shown that the basic physical parameters such as the H− extraction voltage and the effective electron confinement time significantly affect the formation of the plasma meniscus and the resultant beam halo since the penetration of electric field for negative ion extraction depends on these physical parameters. Especially, the electron confinement time depends on the characteristic time of electron escape along the magnetic field as well as the characteristic time of electron diffusion across the magnetic field. The plasma meniscus penetrates deeply into the source plasma region when the effective electron confinement time is short. In this case, the curvature of the plasma meniscus becomes large, and consequently the fraction of the beam halo increases.

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Section: Simulation Modelsupporting

confidence: 73%

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

Miyamoto

Okuda

Nishioka

et al. 2013

Journal of Applied Physics

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“…A series of 2D3V ES-PIC (two-dimensional in real space and three-dimensional velocity space, ES-PIC) modeling has been done in [36][37][38][39][40][41][42]. A reduced-size-scaling has been adopted to save the computational cost by keeping important normalized parameters the same as those in the real system [36,[38][39][40][41][42], e.g., normalized Larmor radius r L, j Lj * r = / collisionality parameter L, jk jk * l l = / where L is the characteristic scale length of the real system, while r Lj and jk l are the Larmor radius and collision mean free path, respectively. The symbols j and k denote particle species.…”

Section: Introductionmentioning

confidence: 99%

“…The simple ES-PIC model in [36][37][38][39][40][41][42] mentioned above has been improved step-by-step through the model validation by comparisons with various experiments and other theoretical/numerical results [44][45][46]. The models give useful insights into the H − extraction process, and also help identify basic and intrinsic mechanisms of various interesting phenomena in the qualitative manner.…”

Section: Introductionmentioning

confidence: 99%

“…Modeling studies in [36][37][38][39][40][41][42] give useful insights in helping to solve these questions, but problems (4) and (5) above have not yet been completely understood. Understanding of the ion-ion plasma and also plasma meniscus (H − emitting surface) shape in such ion-ion plasma are very important in helping to obtain good beam optics and to reduce the beam halo component.…”

Section: Introductionmentioning

confidence: 99%

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Present status of numerical modeling of hydrogen negative ion source plasmas and its comparison with experiments: Japanese activities and their collaboration with experimental groups

et al. 2018

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The present status of kinetic modeling of particle dynamics in hydrogen negative ion (H − ) source plasmas and their comparisons with experiments are reviewed and discussed with some new results. The main focus is placed on the following topics, which are important for the research and development of H − sources for intense and high-quality H − ion beams: (i) effects of non-equilibrium features of electron energy distribution function on volume and surface H − production, (ii) the origin of the spatial non-uniformity in giant multi-cusp arc-discharge H − sources, (iii) capacitive to inductive (E to H) mode transition in radio frequency-inductively coupled plasma H − sources and (iv) extraction physics of H − ions and beam optics, especially the present understanding of the meniscus formation in strongly electronegative plasmas (so-called ion-ion plasmas) and its effect on beam optics. For these topics, mainly Japanese modeling activities, and their domestic and international collaborations with experimental studies, are introduced with some examples showing how models have been improved and to what extent the modeling studies can presently contribute to improving the source performance. Close collaboration between experimental and modeling activities is indispensable for the validation/improvement of the modeling and its contribution to the source design/development. chamber wall (anode) and filaments (cathode). In the latter sources, the RF-electromagnetic field is used to generate and heat plasmas.In this review, we mainly focus on the modeling studies, especially the modeling study of H − source plasmas using kinetic approaches, such as the test particle Monte-Carlo model [14] and particle in cell (PIC) model [14,15], which has been reviewed in [16]. Here, we extend it with some new results. Close collaboration between the experimental and modeling study is very important as it can improve our basic understanding of source plasmas. Various examples of the model validation will be shown through comparisons with experiments and also how modeling studies contribute to the improvement of source performances.As for the multi-cusp arc-discharge source, we will first show a systematic study to help us understand the role of the EEDF on the H − VP in section 2.2. The study has been carried out for a compact multi-cusp arcdischarge source (SHI H − source: Sumitomo Heavy Industry H − source [17,18]) for medical application such as boron neutron capture therapy and the radioisotope production for molecular imaging technology.The SHI H − source is a typical tandem type H − source [19]. In such a tandem type volume sources, the plasma source volume is divided into two regions by the transverse magnetic field (the so-called magnetic filter filed: MF-field) to control the EEDFs and to promote the two step H − VP reactions explained above. Namely, the source volume consists of two regions: (1) the 'driver region' where the electron energy is high and the EV process is promoted, and (2) the 'extraction region' where the electr...

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“…One of the most important factors that determines the beam focusing is the formation of a plasma meniscus, which is the boundary between the source plasma and the beam [21,22]. The meniscus is physically defined as the equipotential surface, where the quasi-neutrality is broken [23,24]. The meniscus plays a role of an electrostatic lens for the first stage of the beam acceleration.…”

Section: Introductionmentioning

confidence: 99%

Characterisation of negative ion beam focusing based on phase space structure

et al. 2020

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Negative ion beam focusing is a key element for advanced applications of negative ion beams such as accelerators for particle physics, compact accelerators for medical fields, and plasma experiments for nuclear fusion because complicated magnetic fields exist both inside of the source plasma and the grid system. In order to understand the beam focusing, phase space structure measurements for a single beamlet have been performed with a research-and-development negative ion source at the National Institute for Fusion Science. A complicated phase space structure is observed in the direction parallel to the filter magnetic field in the vicinity of the plasma grid, while a single-Gaussian beamlet structure is observed in the direction perpendicular to the filter field. Detailed analyses for the phase space structure of the single beamlet reveal that the complicated structure can be identified as a combination of three beam components with different beam axes. The shifts of each axis are also observed to depend on the ratio of the acceleration voltage for the extraction voltage, which may significantly degrade the beamlet focusing.

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Analysis of the H− ion emissive surface in the extraction region of negative ion sources

Cited by 11 publications

References 3 publications

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

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

Present status of numerical modeling of hydrogen negative ion source plasmas and its comparison with experiments: Japanese activities and their collaboration with experimental groups

Characterisation of negative ion beam focusing based on phase space structure

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