KEIO RESEARCHERS INFORMATION SYSTEM

Profile Summary 【 Display / hide 】

Profile Summary 【 Display / hide 】

• Our group focuses on numerical modeling and simulation of multiple-hierarchical complex plasmas, such as low temperature divertor plasmas in magnetic-confinement fusion devices which include the plasma transport, atomic and molecular processes, plasma-material interactions, etc.

Career 【 Display / hide 】

Career 【 Display / hide 】

• 2024.04

  -

  Present

  Keio University, Faculty of Science and Technology, Professor

• 2020.02

  -

  Present

  National Institutes for Quantum and Radiological Science and Technology, Visiting Researcher

• 2026.04

  -

  2027.03

  Kyushu-Univ. Advanced Fusion Research Center

• 2008.04

  -

  2011.03

  Japan Atomic Energy Agency, Sector of Fusion Research and Development, Postdoctoral Fellow

• 2011.04

  -

  2016.03

  Japan Atomic Energy Agency, Sector of Fusion Research and Development, Researcher

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Academic Background 【 Display / hide 】

Academic Background 【 Display / hide 】

• 1998.04

  -

  2002.03

  Keio University, Faculty of Science and Technology, Department of Applied Physics and Physico-Informatics

  University, Graduated

• 2003.04

  -

  2005.03

  Keio University, Graduate School of Science and Technology, School of Fundamental Science and Technology

  Graduate School, Completed, Master's course

• 2005.04

  -

  2008.03

  Keio University, Graduate School of Science and Technology, School of Fundamental Science and Technology

  Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide 】

Academic Degrees 【 Display / hide 】

• Ph.D (Engineering), Keio University, Coursework, 2008.03

  Study of Flow Structure and Transport Process of Heavy Metal Impurity in Tokamak Edge Plasmas

Research Areas 【 Display / hide 】

Research Areas 【 Display / hide 】

• Energy Engineering / Fundamental plasma

• Energy Engineering / Nuclear fusion

Research Keywords 【 Display / hide 】

Research Keywords 【 Display / hide 】

• Plasma

• Computer Simulation

• Fusion

• Divertor Plasma

• Ion source plasma

Papers 【 Display / hide 】

Papers 【 Display / hide 】

• Neutral-density dependence of EIR- and MAR-dominated detachment regimes in hydrogen plasmas with multi-ion-temperature effects

  Natsume H., Tanaka H., Togo S., Sawada K., Hoshino K., Ohno N.

  Physics of Plasmas 33 ( 7 ) 072506 2026.07

  Research paper (scientific journal), Joint Work, Accepted,  ISSN  1070664X

  　View Summary

  A multi-ion-temperature model for hydrogen plasmas has been newly developed and implemented in the linear divertor plasma simulation code LINDA-NU to investigate detachment mechanisms involving atomic and molecular processes. In this model, H⁺, H<inf>2</inf>⁺, and H<inf>3</inf>⁺ ions are treated as separate fluids with independent temperatures, enabling a detailed assessment of ion-species-dependent thermal and momentum dynamics in detached plasmas. Plasma detachment transitions were studied by scanning atomic and molecular neutral densities. An increase in atomic hydrogen density leads to electron–ion recombination-dominated detachment, where charge exchange with atomic neutrals governs momentum loss. In contrast, increasing molecular hydrogen density results in molecular-activated recombination (MAR)-dominated detachment, in which molecular ions become quantitatively significant and strongly influence particle, momentum, and energy balances. A comparison with a simplified single-ion-temperature model demonstrates that the multi-ion-temperature treatment is essential for accurately describing the MAR-dominated regime, where multi-ion temperatures significantly modify molecular reaction rates, leading to qualitative differences in plasma profiles.

  • Access to Document (DOI)

• Code-to-code comparison of SOLPS-ITER and SONIC edge transport codes in JT-60SA tokamak plasma conditions

  Rubino G., Yamoto S., Coster D., Falchetto G., Wiesen S., Sozzi C., Hoshino K., Homma Y., Nakano T., Hayashi N., Aiba N.

  Fusion Engineering and Design 228   115759 2026.07

  Research paper (scientific journal), Joint Work, Accepted,  ISSN  09203796

  　View Summary

  Plasma boundary codes are widely used to interpret and predict SOL/divertor plasmas. The comparison of results obtained by these codes is one of the options to improve the SOL/divertor plasma modelling by defining possible limitations and enhancing the fidelity of future simulations. The aim of this study is to validate the transport models of SOL/divertor transport codes SOLPS-ITER and SONIC by terms-to-terms comparison, from the viewpoint of physical explanation rather than the numerical viewpoint. In this study, the comparison of the results between SOLPS-ITER and SONIC on pure-D plasma conditions with attached and partially detached plasmas in JT-60SA has been performed as a first step of the benchmarking activity. The calculation conditions such as computational grids, boundary conditions, and atomic/molecule database, are set to be as close as possible. In summary, the comparison can be concluded that no substantial difference can be seen although some differences in the plasma parameters have been observed. The main difference can be seen as the higher ratio of pressure drop in SOLPS-ITER than SONIC in front of the divertors in the partially detached case. It was found that the difference can be understood by the following process. The initial difference originated from the electron temperature and ion temperature in the vicinity of divertor plates. The electron temperature in SONIC near outer strike point is slightly higher than that of SOLPS-ITER. The difference in the electron temperature results in broader D+ particle source by ionization of neutrals and higher D+ ion density. Higher D+ ion and neutral densities in SOLPS-ITER leads to a larger momentum loss by charge exchange and thus the plasma loses its pressure. This result suggests that the small difference in the initial plasma parameters can be propagated by the interaction between neutrals, which affects the estimation of degree of detachment.

  • Access to Document (DOI)

• Stability analysis of divertor plasma transport using the CSD model

  Yamada K., Hoshino K., Hatayama A.

  Plasma Physics and Controlled Fusion 68 ( 7 ) 075025 2026.07

  Research paper (scientific journal), Joint Work, Accepted,  ISSN  07413335

  　View Summary

  Thermal instability of divertor plasma transport in steady-state operation is a critical issue in reactor design. Identifying the thermally stable regime is crucial for the successful operation of a fusion reactor. This study aims to explore the regime of stable operation for divertor plasma and to investigate how this stability depends on key engineering parameters. For this purpose, a linear stability analysis is applied to equilibrium solutions of the particle, momentum, and energy balance equations obtained from the core-SOL-divertor model, providing a novel application of point-model-based analysis. In this regard, this study specifically addresses plasma heat control via radiation within the divertor volume. While alternative heat exhaust strategies utilizing strong radiation localized near the X-point—such as the X-point radiator regime—are also highly important, they are outside the scope of this work. Under this framework, this study presents two main findings through model calculations for JT-60U and JA-DEMO. First, the divertor plasma exhibits three thermally stable states: low-recycling, high-recycling, and weakly detached, while the intermediate states between them are unstable. Within the context of the localized divertor-volume radiation, the weakly detached state is identified as the expected operational regime in future fusion reactors. Second, as initial examples demonstrating the capability of the stability analysis framework for future extensive parametric surveys, the stability of the weakly detached state is found to be primarily sensitive to the exhaust power; increasing power raises the lower temperature limit and significantly narrows the stable range. Variations in the major radius have little influence on stability, whereas a reduction in the minor radius slightly raises the lower stability limit within the parameter range examined. The proposed stability evaluation framework provides qualitative guidance for selecting reactor design parameters that expand the stable operational window of divertor plasmas.

  • Access to Document (DOI)

• SONIC simulation studies of power and particle exhaust, and impurity concentration for JA DEMO tokamak design

  Asakura N., Hoshino K., Yamamoto T., Sakamoto Y.

  Nuclear Fusion 66 ( 8 ) 086020 2026.06

  Research paper (scientific journal), Joint Work, Accepted,  ISSN  00295515

  　View Summary

  SONIC divertor code facilitates simultaneous calculations of seeding impurity (Ar) and fusion product (He) transport. D<inf>2</inf> and Ar gases were injected at the outer midplane and upper location of the outer divertor, respectively. He exhausts in the detached divertor have been investigated for a reference series of JA DEMO with an increasing deuterium gas puff rate (50–200 Pa m³s⁻¹) where P<inf>sep</inf> ∼ 250 MW and the radiation fraction is 0.8. The outer divertor heat load (q<inf>tot</inf>^div) peaked in the attached region on the partially detached target, and the peak-q<inf>tot</inf>^div was reduced to lower than 10 MW m⁻² by increasing the D<inf>2</inf> puff rate while maintaining a relatively low n<inf>e</inf>^sep (2 × 10¹⁹ – 2.5 × 10¹⁹m⁻³). Neutral and gas pressures in the divertor (P<inf>D0</inf>^div, P<inf>D2</inf>^div) were evaluated at exhaust slots of the dome and in the sub-divertor. The total pressure (P<inf>Dtot</inf>^div) in the D-puff scan was increased from 1.4 to 3 Pa at the outer exhaust slots, and the outer peak-q<inf>tot</inf>^div was proportional to (P<inf>Dtot</inf>^div)^−0.7. Plasma flow reversals with M<inf>//</inf> = 0.2 – 0.3 were generated near the detach–attach boundary above the outer divertor target. The influence of the flow reversal on the plasma and impurity transport was determined. Convective heat flux was reversed, which significantly affected the ion heat flux profile in the upstream SOL. The flow reversal reduced the impurity shielding and radiation loss in the outer divertor. Inner-enhanced in–out asymmetry of Ar concentration (c<inf>Ar</inf>) was large near the separatrix in SOL, suggesting that Ar ions were transported from the inner SOL to the confined plasma. In the confined plasma (edge), both c<inf>Ar</inf>^edge and c<inf>He</inf>^edge were reduced and poloidally uniform, where c<inf>Ar</inf>^edge was reduced to the marginal level and c<inf>He</inf>^edge was below the design reference by system code assumption (c<inf>Ar</inf>^main: 0.6%, c<inf>He</inf>^main: 7%). Consequently, these SONIC results are generally consistent with the JA DEMO higher-κ design, and larger D-puff (and smaller Г<inf>Ar,puff</inf>) operation is preferable for the large power exhaust in the divertor and the impurity control in the edge plasma.

  • Access to Document (DOI)

• First SOLPS-ITER Simulation Study of Japanese DEMO on Leakage of Seeded Ar Impurity

  Si H., Kawamura G., Asakura N., Hoshino K., Seto H., Sakamoto Y., Yagi M.

  Contributions to Plasma Physics  2026.06

  Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  08631042

  　View Summary

  For JA DEMO, one of the grand challenges is efficiently handling the extreme power loads onto plasma-facing components, particularly the divertor targets. Impurity seeding is an essential strategy for increasing the radiation losses and thereby reducing the heat load on the targets. A critical remaining issue is the trade-off between the retention of radiative impurities in the divertor region to maximize the radiation loss, and their leakage to the upstream region, which degrades the core plasma confinement. To address this issue, based on the current baseline divertor geometry of JA DEMO, the SOLPS-ITER code is applied for the first time to evaluate the divertor power exhaust and Ar impurity distribution across various Ar seeding levels in detail. The simulation results show that increasing the Ar seeding level is highly beneficial for reducing the heat load on the targets. Moreover, in the near SOL there is a strong flow reversal of the main D ions and Ar impurity ions from the lower outer divertor target toward the upstream. This flow reversal promotes the transport of Ar ions out of the lower outer divertor region, leading to significant core contamination. As a result, such leakage severely constrains the viability of using high seeding levels for heat-load control in the current JA DEMO divertor geometry and plasma operating scenario.

  • Access to Document (DOI)

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Papers, etc., Registered in KOARA 【 Display / hide 】

Papers, etc., Registered in KOARA 【 Display / hide 】

• Invesigation of dynamic characteristics of the detached divertor plasma by kinetic modeling

  Hoshino, Kazuo

  科学研究費補助金研究成果報告書 2023

• Development of integrated simulation model for ion source plasmas

  Hoshino, Kazuo

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2023

• Study of impurity transport in boundary plasma of fusion device

  Hoshino, Kazuo

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2018

• Kinetic modeling of fusion edge plasma and dynamic characteristics of detachment plasmas

  Hoshino, Kazuo

  科学研究費補助金研究成果報告書 2017

Reviews, Commentaries, etc. 【 Display / hide 】

Reviews, Commentaries, etc. 【 Display / hide 】

• イオン源の数値シミュレーション技術の進展と応用

  Kenji Miyamoto

  プラズマ・核融合学会誌 97   568 - 596 2021

  Article, review, commentary, editorial, etc. (scientific journal), Joint Work

  • CiNii Research

• 小特集統合コードによる磁場閉じ込め核融合プラズマシミュレーションの現状と今後の展望：　２．統合コードを構成する物理モジュール群

  村上定義，本多充，相羽信行，松山顕之，林伸彦，星野一生，藤田隆明，福山淳，横山雅之

  プラズマ・核融合学会誌 95 ( 09 ) 427 - 436 2019.09

  Article, review, commentary, editorial, etc. (scientific journal), Joint Work

• 小特集　原型炉に向けてのダイバータの研究開発課題ー現状と展望ー：　２．日本における原型炉ダイバータ概念の現状と開発課題

  朝倉伸幸、星野一生

  プラズマ・核融合学会誌 92 ( 12 ) 870 - 876 2016.12

  Article, review, commentary, editorial, etc. (scientific journal), Joint Work

• 小特集　原型炉に向けてのダイバータの研究開発課題ー現状と展望ー：3 非接触プラズマと熱・粒子処理に関するダイバータ実験研究およびモデリングの現状と研究開発課題　3.2 ダイバータモデリング研究

  星野一生

  プラズマ・核融合学会誌 92 ( 12 ) 882 - 885 2016.12

  Article, review, commentary, editorial, etc. (scientific journal), Single Work

• 小特集 DEMOに向けた直線型装置を用いた境界プラズマ、プラズマ・壁相互作用研究： １．直線型プラズマ生成装置の現状と原型炉ダイバータ設計における課題

  坂本瑞樹、大野哲靖、朝倉伸幸、星野一生

  プラズマ・核融合学会誌 90 ( 08 ) 473 - 479 2014.08

  Article, review, commentary, editorial, etc. (scientific journal), Joint Work

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Presentations 【 Display / hide 】

Presentations 【 Display / hide 】

• Comparison of Elastic and Charge-Exchange Collision Models for Fusion Divertor Simulations

  K. Mano, K. Hoshino

  [International presentation]  10th Asia-Pacific Conference on Plasma Physics (AAPPS-DPP2026) (Busan, Korea) , 

  2026.10

  , 

  Poster presentation

• Development of a PIC Model for Divertor Plasmas of Fusion DEMO Reactors

  K. Ishikawa, K. Hoshino

  [International presentation]  10th Asia-Pacific Conference on Plasma Physics (AAPPS-DPP2026) (Busan, Korea) , 

  2026.10

  , 

  Poster presentation

• PIC Simulation of Sheath Formation and Particle Loss Processes in Cusp Magnetic Fields for Negative Ion Sources

  T. Otsubo, K. Hoshino

  [International presentation]  10th International Symposium on Negative Ions, Beams and Sources (NIBS2026) (Nelson, Canada) , 

  2026.09

  , 

  Poster presentation

• Direct comparison of extraction electrode current between experiments and PIC simulation in J-PARC RF-driven negative hydrogen ion source

  T. Shibata, H. Nakano, H. Soejima, H. Oguri, K. Shinto, K. Hayashi, K. Hoshino, K. Miyamoto, K. Tobita, K. Nanmo, K. Ohkoshi M. Wada, N. Kawamura, R. Kitamura, T. Segawa

  [International presentation]  10th International Symposium on Negative Ions, Beams and Sources (NIBS2026) (Nelson, Canada) , 

  2026.09

  , 

  Poster presentation

• Analysis of isotope effects on negative ion source extraction using 3D-PIC Calculation

  K. Hayashi, K. Miyamoto, H. Nakano, K. Hoshino, A. Hatayama, H. Soejima, N. Kawamura, T. Shibata

  [International presentation]  10th International Symposium on Negative Ions, Beams and Sources (NIBS2026) (Nelson, Canada) , 

  2026.09

  , 

  Poster presentation

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

Research Projects of Competitive Funds, etc. 【 Display / hide 】

• 高周波負イオン源における引出領域の電磁場応答の数値シミュレーション

  2026.04

  -

  2030.03

  Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Coinvestigator(s)

  　View Summary

  本研究は、核融合・高エネルギー加速器に不可欠な高周波(RF)負イオン源の根本的性能限界である悪いビーム収束性の原因を解明し、その革新的改善策を提示することを目的とする。RF負イオン源でビーム収束性が悪い理由として、RF電磁場による引出界面の振動や高い負イオン温度が指摘されている。そこで本研究では、RF負イオン源のプラズマ生成部から負イオン引出・加速領域を総括的にモデル化し、シースや引出界面の形成過程と負イオンビーム引出領域における負イオン輸送過程を解析する。RF負イオン源でビームの収束性を制限する物理的要因を突き止め、高性能RF負イオン源の設計指針を提示する。

• Understanding energy and momentum losses associated with the generation and transport of excited particles and control of detached recombining plasma

  2024.04

  -

  2028.03

  Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Coinvestigator(s)

  　View Summary

  磁場閉じ込めプラズマ核融合炉の実現のためには，炉心プラズマから周辺領域に流出する膨大な粒子流および熱流を制御し，直接プラズマと接触するプラズマ対向材(ダイバータ板)の損傷を低減することが最重要課題の一つとなっている。熱負荷低減法として，非接触再結合プラズマ（Detached Recombining Plasmas）形成による熱流制御法の確立の重要性が指摘されている。本研究では，直線型高密道プラズマ発生装置を用いた実験と流体コード，中性粒子輸送コードをカップリングした統合コードによる解析により，非接触再結合プラズマの生成機構と制御手法を確立し，核融合発電の早期実現に資する。

• ダイバータ配位プラズマの境界層におけるプラズマ流と不純物輸送へのドリフトの効果

  2022.04

  -

  2026.03

  Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Coinvestigator(s)

  　View Summary

  内部コイルを用いてダイバータ配位の環状プラズマを生成し、その境界層におけるプラズマ流や不純物イオンの流速などを詳細に計測する。三角形度などプラズマ断面形状を様々に変えた実験を実施し、ダイバータプラズマシミュレーションコードの結果と比較する。これにより、プラズマ流に対するイオンドリフトの効果を明らかにするとともに実験的な裏付けのある不純物輸送モデルを提案する。

• Elucidation and control of the physical and chemical mechanisms governing the spatio-temporal structure of detached recombining plasmas

  2020.04

  -

  2024.03

  Nagoya University, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), Research grant, Coinvestigator(s)

  　View Summary

  プラズマプロセッシングや核融合研究において重要な課題となっている気相中で消えるプラズマの物性を明らかにする。電子・イオン再結合（三体再結合，放射再結合）が主要な過程となる再結合プラズマ中の非熱平衡性，電位構造に関連した熱・粒子輸送過程を，直線型高密度プラズマ発生装置を用いた基礎実験とシミュレーションとの相補的な研究により明らかにする。また，振動励起水素分子により駆動される再結合（分子駆動再結合）プラズマ生成に関して，固体壁で生成される振動・回転励起水素分子の影響と同位体効果を明らかにする。さらに，再結合プラズマのパルス応答を高時間分解で調べ，時空間変化を決定する物理・化学過程を明らかにする。

• Theoretical study of the physical mechanism of isotope effects in deuterium negative ion sources

  2019.04

  -

  2022.03

  Naruto University of Education, Grants-in-Aid for Scientific Research, Kenji Miyamoto, Grant-in-Aid for Scientific Research (C), Coinvestigator(s)

  　View Summary

  In this study, the cause of the increase in electron current, which is one of the isotope effects in a deuterium negative ion source, was investigated using both an analysis with a zero-dimensional model that takes into account the atomic and molecular collision processes between hydrogen and deuterium, and a numerical simulation for electron transport analysis (KEIO-MARC code).
  First, for the zero-dimensional model, the results shows that the plasma density is approximately 1.7 times higher for deuterium due to differences in the effective reaction rate coefficients for ionization of hydrogen and deuterium and the transport loss time constant of positive ions. Similar results are also obtained with the KEIO-MARC code. From the above, it is made clear that the increase in electron current due to deuteration is caused by differences in the effective reaction rate coefficients for ionization and the effective confinement time of positive ions.

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Awards 【 Display / hide 】

Awards 【 Display / hide 】

• 核融合大型計算機利用研究優秀賞

  2024.09, 国立研究開発法人　量子科学技術研究開発機構

  Type of Award： Other

Courses Taught 【 Display / hide 】

Courses Taught 【 Display / hide 】

• BACHELOR'S THESIS

  2026

• COMPUTATIONAL PHYSICS

  2026

• APPLIED PHYSICS AND PHYSICO-INFORMATICS LABORATORY C

  2026

• DOCTORAL RESEARCH ON MATHEMATICAL AND PHYSICAL SCIENCES

  2026

• INDEPENDENT STUDY ON FUNDAMENTAL SCIENCE AND TECHNOLOGY

  2026

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Memberships in Academic Societies 【 Display / hide 】

Memberships in Academic Societies 【 Display / hide 】

• The Japan Society of Plasma Science and Nuclear Fusion Research, 

  2001.08

  -

  Present

• Japan Society for Simulation Technology, 

  2022.07

  -

  Present

• The Physical Society of Japan, 

  2026.06

  -

  Present

Committee Experiences 【 Display / hide 】

Committee Experiences 【 Display / hide 】

• 2026.05

  -

  2027.12

  Local Organizing Committee of PET21 (21st International Workshop of Plasma Edge Theory in Fusion Devices)

• 2024.04

  -

  2026.03

  代議員, 一般社団法人 プラズマ・核融合学会

• 2021.09

  -

  Present

  Member of the International Scientific Committee of Plasma Edge Theory in Fusion Devices

• 2019.12

  -

  2025.03

  核融合エネルギーフォーラム専門委員

• 2019.07

  -

  Present

  炉心プラズマ共同企画委員会　理論シミュレーション専門部会　専門委員, 量子科学技術研究開発機構

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