研究者詳細 - 星野　一生

論文 - 星野　一生

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Analysis of plasma meniscus in a hydrogen electronegative plasma

Miyamoto K., Hayashi K., Hoshino K., Hatayama A.

Plasma Sources Science and Technology 31 （ 10 ） 105012 2022年11月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 09630252

The emitting surface of an ion beam (plasma meniscus) in the vicinity of the extraction aperture is theoretically investigated. In the present study, the electrons, H+ ions and volume produced H− ions are contained in the electronegative plasma. By solving the one-dimensional Poisson equation, an analytical formula is obtained from the balance between the current reaching a wall and the space charge limited current of negatively charged particles. The analytical formula indicates that the distance, d eff, between the plasma meniscus and the extraction grid includes the ratio of masses of the negative ions and electrons, which is different from that for a plasma containing electrons and single positive ions, and depends on the ratio of the negative ion density to the electron density, α. With increase in the value of α, the distance d eff becomes shorter, and thus the penetration of the electric field for negative ion extraction into the source plasma becomes smaller. This tendency is confirmed by using a three-dimensional particle-in-cell simulation from the results of the contour map of the electrostatic potential near the plasma grid and the location of the plasma meniscus. The reasons why the distance d eff becomes shorter with increase in the value of α are considered to be the larger space charge effect of the negative ions compared with that of the electrons and the decrease in the plasma potential.

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Plasma physics and control studies planned in JT-60SA for ITER and DEMO operations and risk mitigation

Yoshida M., Giruzzi G., Aiba N., Artaud J.F., Ayllon-Guerola J., Balbinot L., Beeke O., Belonohy E., Bettini P., Bin W., Bierwage A., Bolzonella T., Bonotto M., Boulbe C., Buermans J., Chernyshova M., Coda S., Coelho R., Davis S., Day C., De Tommasi G., Dibon M., Ejiri A., Falchetto G., Fassina A., Faugeras B., Figini L., Fukumoto M., Futatani S., Galazka K., Garcia J., Garcia-Muñoz M., Garzotti L., Giacomelli L., Giudicotti L., Hall S., Hayashi N., Hoa C., Honda M., Hoshino K., Iafrati M., Iantchenko A., Ide S., Iio S., Imazawa R., Inoue S., Isayama A., Joffrin E., Kamiya K., Ko Y., Kobayashi M., Kobayashi T., Kocsis G., Kovacsik A., Kurki-Suonio T., Lacroix B., Lang P., Lauber P., Louzguiti A., De La Luna E., Marchiori G., Mattei M., Matsuyama A., Mazzi S., Mele A., Michel F., Miyata Y., Morales J., Moreau P., Moro A., Nakano T., Nakata M., Narita E., Neu R., Nicollet S., Nocente M., Nowak S., Orsitto F.P., Ostuni V., Ohtani Y., Oyama N., Pasqualotto R., Pégourié B., Perelli E., Pigatto L., Piccinni C., Pironti A., Platania P., Ploeckl B., Ricci D., Roussel P., Rubino G., Sano R., Särkimäki K., Shinohara K., Soare S., Sozzi C., Sumida S., Suzuki T., Suzuki Y.

Plasma Physics and Controlled Fusion 64 （ 5 ） 054004 2022年05月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 07413335

A large superconducting machine, JT-60SA has been constructed to provide major contributions to the ITER program and DEMO design. For the success of the ITER project and fusion reactor, understanding and development of plasma controllability in ITER and DEMO relevant higher beta regimes are essential. JT-60SA has focused the program on the plasma controllability for scenario development and risk mitigation in ITER as well as on investigating DEMO relevant regimes. This paper summarizes the high research priorities and strategy for the JT-60SA project. Recent works on simulation studies to prepare the plasma physics and control experiments are presented, such as plasma breakdown and equilibrium controls, hybrid and steady-state scenario development, and risk mitigation techniques. Contributions of JT-60SA to ITER and DEMO have been clarified through those studies.

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Development and Application of SONIC Divertor Simulation Code to Power Exhaust Design of Japanese DEMO Divertor

Asakura N., Hoshino K., Homma Y., Sakamoto Y.

Processes （Processes） 10 （ 5 ） 872 2022年04月

研究論文（学術雑誌）, 共著, 査読有り

An integrated divertor simulation code, SONIC, An integrated divertor simulation code, SONIC, has been developed in order to predict a self-consistent transport solution of the plasma, neutral and impurities in the scrape-off layer (SOL) and divertor. SONIC code has contributed to determining the divertor design and power handling scenarios for the Japanese (JA) fusion demonstration (DEMO) reactor. Radiative cooling scenario of Ar impurity seeding and the divertor performance have been demonstrated to evaluate the power exhaust scenarios with . The simulation identified the decay length of the total parallel heat flux profile as being broader than the electron one, because of the ion convective transport from the outer divertor to the upstream SOL, produced by the plasma flow reversal. The flow reversal also reduced the impurity retention in the outer divertor, which may produce the partial detachment. Divertor operation margin of key power exhaust parameters to satisfy the peak was determined in the low of under severe conditions such as reducing radiation loss fraction, i.e., and diffusion coefficients and . The divertor geometry and reference parameters rad) were consistent with the low operation of the JA DEMO concepts. For either severe assumption of or and to their half values, higher operation was required. In addition, recent investigations of physics models (temperature-gradient force on impurity, photon transport, neutral-neutral collision) under the DEMO relevant SOL and divertor condition are presented.

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Study of negative ion beam emittance characteristic using 3D PIC-MCC simulation

Miyamoto K., Nagaoka K., Hatayama A., Hoshino K., Nakano H., Shibata T., Tsumori K.

Journal of Physics: Conference Series 2244 （ 1 ） 012040 - 012040 2022年04月

研究論文（国際会議プロシーディングス）, 共著, 査読有り, ISSN 17426588

It is reported from the measurement of a negative ion beamlet emittance that the characteristic three-Gaussian components are observed in the emittance diagram. The negative ion trajectories are calculated using 3D PIC-MCC simulation in order to clarify the origin of this complicated phase space structure and underlying physical mechanism. The characteristic three-Gaussian components can be reproduced in the emittance diagram from the simulation result. It is verified that the Gaussian components are caused by the negative ions extracted from the different plasma meniscus region, that is, the central region or the region near the edges of the meniscus.

Numerical study of different electron density observed in Hydrogen and Deuterium ion source plasmas

Shibata T., Kato R., Nakano H., Hayashi K., Sato J., Miyamoto K., Hoshino K., Hatayama A.

Journal of Physics: Conference Series 2244 （ 1 ） 012002 - 012002 2022年04月

研究論文（国際会議プロシーディングス）, 共著, 査読有り, ISSN 17426588

Sequences of hydrogen (H) and deuterium (D) experiments have been done by NIFS research and development negative ion source (RNIS) for the deuterium NBI development. In the experiments, the co-extracted electron current with the negative ions and the electron density in the plasma generation region in the D experiment have been around three times higher than that in the H experiment. To explain the difference of the electron density in the RNIS driver region, a zero-dimensional numerical model is developed in the present study. The model only focuses on the isotope effect for vibrationally excited level of electronically grounded state molecules and its relevant cross-sections. The calculation results show that difference of the ionization channel numbers via molecular vibrationally excited states could be a reason to enhance ionization rate in D plasma.

Numerical analysis of isotope effect in NIFS negative ion source

Kato R., Hoshino K., Nakano H., Shibata T., Miyamoto K., Iwanaka K., Hayashi K., Hatayama A.

Journal of Physics: Conference Series 2244 （ 1 ） 012035 - 012035 2022年04月

研究論文（国際会議プロシーディングス）, 共著, 査読有り, ISSN 17426588

Result of hydrogen (H) and deuterium (D) experiments done by NIFS research and development negative ion source (RNIS) demonstrated that the co-extracted electron current with the negative ions and the electron density in the driver region in the D experiment have been around three times higher than that in the H experiment. To investigate mechanism of this difference, electron transport simulation using 3D kinetic particle tracking model KEIO-MARC code has been modified and applied to analysis of the isotope effect in the NIFS negative ion source. Simulation result suggests that impacts of isotope effects of sheath potential drop, coulomb collisions, and some reactions of ground state molecules and ions on the electron density is not large to explain the experimental result of the increase in the electron density in the plasma.

Completion of JT-60SA construction and contribution to ITER

Kamada Y., Di Pietro E., Hanada M., Barabaschi P., Ide S., Davis S., Yoshida M., Giruzzi G., Sozzi C., Abdel Maksoud W., Abe H., Aiba N., Akiyama T., Ayllon-Guerola J., Arai T., Artaud J.F., Asakura N., Ashikawa N., Balbinot L., Bando T., Baulaigue O., Belonohy E., Bin W., Bombarda F., Bolzonella T., Bonne F., Bonotto M., Botija J., Cabrera-Pérez S., Cardella A., Carraro L., Cavalier J., Chernyshova M., Chiba S., Clement-Lorenzo S., Cocilovo V., Coda S., Coelho R., Coffey I., Collin B., Corato V., Cucchiaro A., Czarski T., Dairaku M., Davis S., Day C., de la Luna E., De Tommasi G., Decool P., Di Pace L., Di Pietro E., Dibon M., Disset G., Ejiri A., Endo Y., Ezumi N., Falchetto G., Fassina A., Fejoz P., Ferro A., Fietz W., Figini L., Fornal T., Frello G., Fujita T., Fukuda T., Fukui K., Fukumoto M., Furukawa M., Futatani S., Gabellieri L., Gaio E., Galazka K., Garcia J., Garcia-Dominguez J., Garcia-Lopez J., Garcia-Munoz M., Garzotti L., Gasparini F., Gharafi S., Giacomelli L., Ginoulhiac G., Giruzzi G., Giudicotti L., Guillén González R., Hajnal N., Hall S., Hamada K., Hanada K., Hanada M., Hasegawa K., Hatae T., Hatakeyama S., Hauer V., Hayashi N., Hayashi T., Heller R., Higashijima S., Hinata J.

Nuclear Fusion 62 （ 4 ） 042002 2022年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 00295515

Construction of the JT-60SA tokamak was completed on schedule in March 2020. Manufacture and assembly of all the main tokamak components satisfied technical requirements, including dimensional accuracy and functional performances. Development of the plasma heating systems and diagnostics have also progressed, including the demonstration of the favourable electron cyclotron range of frequency (ECRF) transmission at multiple frequencies and the achievement of long sustainment of a high-energy intense negative ion beam. Development of all the tokamak operation control systems has been completed, together with an improved plasma equilibrium control scheme suitable for superconducting tokamaks including ITER. For preparation of the tokamak operation, plasma discharge scenarios have been established using this advanced equilibrium controller. Individual commissioning of the cryogenic system and the power supply system confirmed that these systems satisfy design requirements including operational schemes contributing directly to ITER, such as active control of heat load fluctuation of the cryoplant, which is essential for dynamic operation in superconducting tokamaks. The integrated commissioning (IC) is started by vacuum pumping of the vacuum vessel and cryostat, and then moved to cool-down of the tokamak and coil excitation tests. Transition to the super-conducting state was confirmed for all the TF, EF and CS coils. The TF coil current successfully reached 25.7 kA, which is the nominal operating current of the TF coil. For this nominal toroidal field of 2.25 T, ECRF was applied and an ECRF plasma was created. The IC was, however, suspended by an incident of over current of one of the superconducting equilibrium field coil and He leakage caused by insufficient voltage holding capability at a terminal joint of the coil. The unique importance of JT-60SA for H-mode and high-β steady-state plasma research has been confirmed using advanced integrated modellings. These experiences of assembly, IC and plasma operation of JT-60SA contribute to ITER risk mitigation and efficient implementation of ITER operation.

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Impact of neutral gas puffing on the divertor power exhaust and particle control in GAMMA 10/PDX by the LINDA-KNMC code

Islam M.S., Nakashima Y., Hatayama A., Hoshino K., Sakamoto M.

Contributions to Plasma Physics 62 （ 5-6 ） e202100141 2021年12月

研究論文（国際会議プロシーディングス）, 共著, 査読有り, ISSN 08631042

This paper numerically investigates the impact of neutral gas puffing on the divertor power exhaust and particle control in GAMMA 10/PDX applying the plasma fluid code LINDA and the kinetic neutral code KMNC. The LINDA code is applied to GAMMA 10/PDX plasmas for understanding the physics of detachment and energy loss processes. The LINDA code is coupled with a Monte–Carlo neutral code for describing the hydrogen (H and H2) neutral particles. The plasma ion temperature (Ti) is reduced towards the target plate with the increment of H2 Gas-Puff rate. This paper also numerically investigates the impact of recombination processes on the detached formation. The ionization, charge–exchange, and recombination of H have been included as a particle and an energy sink and source parts of the fluid equations. The reaction rate coefficient of molecular activated recombination (MAR) has been recently introduced in the LINDA code. In this paper, we study numerically the effect of MAR on the detached plasma. The MAR plays a dominant role in making the detached plasma. The simulation clarified that H neutral particles injection can effectively generate the detached plasma by enhancing the plasma-neutral collisions processes.

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Power exhaust concepts and divertor designs for Japanese and European DEMO fusion reactors

Nobuyuki Asakura, Kazuo Hoshino, Satoshi Kakudate, Fabio Subba, Christian Vorpahl, Yuki Homma, Hiroyasu Utoh, Youji Someya, Yoshiteru Sakamoto, Ryoji Hiwatari, Satoshi Suzuki, Jeong-Ha You, Mattia Siccinio, Gianfranco Federici

Nuclear Fusion （{IOP} Publishing） 61 （ 12 ） 126057 2021年10月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 00295515

Concepts of the power exhaust and divertor design have been developed, with a high priority in the pre-conceptual design phase of the Japan-Europe broader approach DEMO design activity (BA DDA). Common critical issues are the large power exhaust and its fraction in the main plasma and divertor by the radiative cooling (P radtot/P heat 0.8). Different exhaust concepts in the main plasma and divertor have been developed for Japanese (JA) and European (EU) DEMOs. JA proposed a conventional closed divertor geometry to challenge large P sep/R p handling of 30-35 MW m-1 in order to maintain the radiation fraction in the main plasma at the ITER-level (f radmain = P radmain/P heat ∼ 0.4) and higher plasma performance. EU challenged both increasing f radmain to ∼0.65 and handling the ITER-level P sep/R p in the open divertor geometry. Power exhaust simulations have been performed by SONIC (JA) and SOLPS5.1 (EU) with corresponding P sep = 250-300 MW and 150-200 MW, respectively. Both results showed that large divertor radiation fraction (P raddiv/P sep 0.8) was required to reduce both peak q target (10 MW m-2) and T e,idiv. In addition, the JA divertor performance with EU-reference P sep of 150 MW showed benefit of the closed geometry to reduce the peak q target and T e,idiv near the separatrix, and to produce the partial detachment. Integrated designs of the water cooled divertor target, cassette and coolant pipe routing have been developed in both EU and JA, based on the tungsten (W) monoblock concept with Cu-alloy pipe. For year-long operation, DEMO-specific risks such as radiation embrittlement of Cu-interlayers and Cu-alloy cooling pipe were recognized, and both foresee higher water temperature (130 °C-200 °C) compared to that for ITER. At the same time, several improved technologies of high heat flux components have been developed in EU, and different heat sink design, i.e. Cu-alloy cooling pipes for targets and RAFM steel ones for the baffle, dome and cassette, was proposed in JA. The two approaches provide important case-studies of the DEMO divertor, and will significantly contribute to both DEMO designs.

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Study of numerical error of a Eulerian-Lagrangian scheme in the presence of particle source

Ryoko Tatsumi, Kazuo Hoshino, Akiyoshi Hatayama

Computer Physics Communications （Elsevier {BV}） 264 107960 2021年07月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 00104655

Eulerian–Lagrangian (EL–LG) scheme is a numerical scheme that tracks pseudo particles in Eulerian cells. It is widely used in the computational fluid dynamics, however, numerical errors associated with a particle source term has not yet been investigated much. Hence this study focuses on numerical errors of EL–LG caused by particle sources. The purposes are: (i) to clarify causes and situations that bring larger numerical errors by source terms and (ii) to suggest an idea to reduce them. For those purposes, we focus on the particle continuity equation and carry out systematic analysis of the numerical error by setting the following three simple cases: Case (A) No source, Case (B) Constant source, and Case (C) source with arbitrary spatial profile. For each case, we have obtained a theoretical expression of the numerical error. It has been clarified that the errors become relatively large when (i) the spatial profile of the particle source has a large gradient and (ii) the source is localized in the region with high flow-velocity. These were caused by the treatment of the particle source: If pseudo particles due to the source are added in a simple way at the start or the end of the time step, this can lead to larger numerical errors. To reduce those errors, a time-averaging scheme has been suggested. Although the analyzed cases are simple, the results obtained in this study would give important knowledge and insight into numerical errors associated with particle sources in EL–LG schemes.

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Numerical Simulation Study of the Magnetic Flux Tube Expansion on the Divertor Plasma Parameters by the LINDA Code

ISLAM Md. Shahinul, NAKASHIMA Yousuke, ISHIGURO Seiji, HOSHINO Kazuo, HATAYAMA Akiyoshi, HASEGAWA Hiroki, SAKAMOTO Mizuki

Plasma and Fusion Research （一般社団法人プラズマ・核融合学会） 16 （ 0 ） 2403049 - 2403049 2021年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 18806821

In this research, we investigate the effect of magnetic flux tube expansion on the divertor plasma parameters by using the fluid code "LINDA". A comparison between the cylindrical flux tube (without the magnetic flux expansion) and the expansion magnetic flux tube has been undertaken. The aim of the study is to understand the impact of magnetic field expansion on the divertor physics by using the LINDA fluid code. The plasma density (ni) is decreased and parallel velocity is increased (ui||) toward the target plate with the expansion of magnetic field lines near the target plate. The heat and particle fluxes are reduced significantly on the target plate in the case of the expansion mesh configuration. For the case of cylindrical mesh, advection becomes stronger with the decreasing distance from the target plate. In the case of expansion mesh, diffusion is stronger with the decreasing distance from the target plate. These outcomes clearly indicate the effect of the magnetic field structure on the divertor plasma parameters.

Simulation studies of divertor detachment and critical power exhaust parameters for Japanese DEMO design

Asakura N., Hoshino K., Homma Y., Sakamoto Y.

Nuclear Materials and Energy 26 100864 2021年03月

研究論文（国際会議プロシーディングス）, 共著, 査読有り

© 2020 The Author(s) Handling of a large thermal power exhausted from the confined plasma is one of the most important issues for ITER and DEMO. A conventional divertor, which has the closed geometry similar to that of ITER and longer leg of 1.6 m, was proposed for the Japanese (JA) DEMO reactor (Rp/ap = 8.5/2.42 m). A radiative cooling scenario of Ar impurity seeding and the divertor performance have been demonstrated by SONIC simulation, in order to evaluate the power exhaust in JA-DEMO 2014 (primary design with Psep ~ 283 MW) and JA-DEMO with higher plasma elongation (a revised design with Psep ~ 235 MW). The divertor operation with the peak qtarget ≤ 10 MWm−2 was determined in the low nesep of 2–3 × 1019 m−3 under the severe conditions of reducing radiation loss fraction, i.e. f*raddiv = (Pradsol + Praddiv)/Psep, and diffusion coefficients (χ and D). The divertor geometry and reference key parameters (f*raddiv ~ 0.8, χ = 1 m2/s and D = 0.3 m2/s) were so far consistent with the power exhaust concepts in the nesep range, and the revised JA-DEMO design has advantages of wider nesep range and enough margin for the divertor operation. For either severe assumption of f*raddiv ~ 0.7 or χ and D to the half value, higher nesep operation was required for the primary design in order to control the peak qtarget ≤ 10 MWm−2, i.e. the operation window was reduced. Applying the two severe assumptions, the divertor operation was difficult in the low nesep range for the both designs.

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Detached helium plasma simulation by a one-dimensional fluid code with detailed collisional-radiative model

Tanaka H., Saeki I., Ohno N., Kajita S., Ido T., Natsume H., Hatayama A., Hoshino K., Sawada K., Goto M.

Physics of Plasmas 27 （ 10 ） 102505 2020年10月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1070664X

© 2020 Author(s). To increase the accuracy of a particle, momentum, and energy source terms in the detached helium plasma simulation, rate coefficients with the collisional-radiative model were introduced into the fluid code LINear Divertor Analysis (LINDA). Obtained effective rate coefficients and related source terms were compared with those from the conventional empirical databases. It is shown that a high-density condition in future fusion devices causes larger deviation between the effective and the empirical source terms. One-dimensional detached plasma simulation indicated that the peak amplitude of the plasma density during the rollover is sensitive to the source term difference related to the recombination. This study additionally revealed that the heating effect in the three-body recombination process strongly affects the detached plasma formation and downstream plasma parameters.

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Study of the Transient Behavior of Detached Plasma during Xe Gas Injection into the D-Module of GAMMA 10/PDX

ISLAM Md. Shahinul, HOSHINO Kazuo, HATAYAMA Akiyoshi, HASEGAWA Hiroki, ISHIGURO Seiji, MATSUURA Hiroto, SAKAMOTO Mizuki, NAKASHIMA Yousuke, IIJIMA Takaaki, NOJIRI Kunpei, EZUMI Naomichi, YOSHIKAWA Masayuki, KARIYA Tsuyoshi, MINAMI Ryutaro, HIRATA Mafumi

Plasma and Fusion Research （一般社団法人プラズマ・核融合学会） 15 （ 0 ） 1402074 - 1402074 2020年10月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1880-6821

The transition phenomenon of detached plasma during additional heating effects has been studied by applying a short pulse (25 ms) of Electron Cyclotron Heating (ECH) at the east plug-cell of the tandem mirror device GAMMA 10/PDX. In this paper, the plasma parameters on the target plate of the D-module are studied for understanding the impact of transient heating pulse on the sustainability of the detached plasma. The heat flux increases on the target plate for the additional heating case in comparison to without heating pulse. The ion flux also increases when the ECH heating is activated. The electron density enhances significantly during the ECH heating pulse application period. Furthermore, the electron density and the ion flux increase according to the increment of Xe plenum pressure in the case of ECH heating condition. The experimental results clarified that ECH heating pulse can drive the detachment state to attached state in spite of strong effect of Xe gas for generating the detached plasma.

Study of multiple impurity seeding effect using SONIC integrated divertor code for JT-60SA plasma prediction

Yamoto S., Hoshino K., Homma Y., Nakano T., Hayashi N.

Contributions to Plasma Physics 60 （ 5-6 ） e201900146 2020年07月

研究論文（国際会議プロシーディングス）, 共著, 査読有り, ISSN 08631042

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim In order to study the potential impurity seeding operation regime of the future fusion devices, the first application of the integrated divertor code SONIC to the Ar + Ne mixed-impurity seeding operation of JT-60SA steady-state high-β plasma has been carried out. In the case, Ne is added to Ar-only seeding, the separatrix electron density has fell into the desired low separatrix electron density of the scenario. This is mainly because the D+ flow velocity towards the inner divertor has been increased by the Ne seeding. The resultant friction force transports Ar impurities towards the inner divertor region, while impurities are stagnated in the top of scrape-off layer (SOL) in the Ar-only seeding case. The higher impurity radiation power in the divertor regions and lower one in the SOL region above the X point have been obtained in mixed-impurity seeding cases, which show similar tendency as the Ar + Ne mixed-impurity seeding experiment in JT-60 U. At the core edge, Zeff has been slightly increased and the radiation power has been decreased as the Ne seeding rate increases. The core plasma/impurity transport has been also evaluated by the TOPICS code using the impurity density at the core edge computed by the SONIC as a boundary parameter. The results show lower Zeff and radiation power, and higher electron temperature in the core in the mixed-impurity seeding cases. Above possible contributors to the better energy confinement indicate that the mixed-impurity seeding operation might be more effective than Ar-only seeding operation.

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First EMC3-EIRENE modelling of JT-60SA edge plasmas with/without resonant magnetic perturbation field

Tanaka H., Kawamura G., Hoshino K., Kobayashi M., Matsunaga G., Suzuki Y., Lunt T., Feng Y., Ohno N.

Contributions to Plasma Physics 60 （ 5-6 ） e201900114 2020年07月

研究論文（国際会議プロシーディングス）, 共著, 査読有り, ISSN 08631042

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The first EMC3-EIRENE modelling for the JT-60SA edge plasmas with/without the resonant magnetic perturbation field (RMP) was conducted. Both core degradation in the vacuum approximation and strike-point splitting were observed due to the application of the RMP, as in previous studies in other devices. Toroidally averaged divertor heat fluxes with and without the RMP were fitted by using a one-dimensional diffusive model function, showing similar profiles. To extract the modulation components of the divertor heat flux profile, the proper orthogonal decomposition (POD) method was applied. By using the POD outputs, a modulation ratio with respect to the toroidally averaged profile was quantitatively calculated.

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Comparison of the Process Systems Code with the SONIC Divertor Code

Morris J., Asakura N., Homma Y., Hoshino K., Kovari M.

IEEE Transactions on Plasma Science 48 （ 6 ） 1799 - 1803 2020年06月

研究論文（国際会議プロシーディングス）, 共著, 査読有り, ISSN 00933813

© 1973-2012 IEEE. In a demonstration (DEMO) reactor, mitigation of the large heat load on the divertor target to the below material and engineering limits is a key requirement for operation. Systems modeling is used to design entire fusion power plants and, therefore, has to be able to appropriately capture the divertor challenge. Therefore, it is important to validate these models against comprehensive SOL-divertor simulation codes and experiments. A 1-D divertor model in PROCESS was investigated, compared to the results of 2-D SONIC simulation under the detachment condition. The comparison shows how the 1-D divertor model handles the power loss mechanisms from the outboard mid-plane to the outer divertor target for a DEMO-like condition. The results show good agreement on the calculated value of the total power crossing the separatrix (<5% difference) and the total impurity radiation power P imp (<10% difference). However, the 1-D profiles show differences in density and temperature at the upstream of the target (<10 m of connection length to target, corresponding to 10 cm in the poloidal length). One reason for this difference is that the 2-D model calculates impurity transport, which produces a variable impurity fraction along the connection length in the divertor, while the 1-D model uses a single averaged value. The SONIC code also considers physical processes not covered in the 1-D model, such as radial transport in the SOL and divertor region. A scan of P sep values in PROCESS for a DEMO-sized machine show that above Psep = 200 MW, there is a stronger impact on cost and machine size for higher Psep.

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Effect of collisionality dependence of thermal force on impurity transport under a lower collisional condition in DEMO scrape-off layer plasma

Homma Y., Hoshino K., Yamoto S., Tokunaga S., Asakura N., Sakamoto Y.

Nuclear Fusion 60 （ 4 ） 046031 2020年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 00295515

© 2020 IAEA, Vienna. A preceding study (Homma et al 2018 Contrib. Plasma Phys. 58 629-37) presented an advanced model for thermal force whose applicable condition is extended from collisional to relatively low collisional plasma. According to this extended model, the thermal force reduces when plasma collisionality decreases. In the present study, the extended thermal force model has been implemented into a SOL-divertor integrated simulation code SONIC, in order to study the impact on impurity transport in DEMO-relevant scrape-off layer (SOL) plasma, due to thermal force reduction. A set of test simulations has been carried out supposing a reference steady-state operation scenario of the Japanese DEMO fusion reactor concept (JA DEMO). The thermal force has reduced by as much as 20%-70%, reflecting relatively lower collisionality in DEMO SOL plasma. The simulation results have demonstrated that the introduction of the collisionality dependence of thermal force leads to as much as 20%-80% of effective decrease in impurity density and its content ratio widely over the SOL upstream area under the DEMO relevant condition. Compared to the case with the conventional thermal force model, relative change rate of impurity content at representative poloidal positions are as follows: low-field side (LFS) X-point-59%, poloidal top area-22%, HFS upstream area up to-80%, and no major impact around LFS upstream.

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IMPGYRO: The full-orbit impurity transport code for SOL/divertor and its successful application to tungsten impurities

Yamoto S., Homma Y., Hoshino K., Toma M., Hatayama A.

Computer Physics Communications 248 106979 2020年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 00104655

© 2019 Elsevier B.V. In future fusion reactors, tungsten (W) is currently regarded as one of the most feasible candidates for the plasma-facing components (PFCs). Once the W impurities sputtered from the PFCs penetrate into the core plasma, the large radiation cooling and fuel dilution, which leads to the deterioration of the core plasma performance, take place. To understand and to control W impurity transport are indispensable for future fusion reactors. In order to understand W transport, we are continuing to develop the kinetic impurity transport code IMPGYRO for SOL/divertor in fusion reactors. The IMPGYRO has obtained following unique features compared to other existing kinetic impurity transport codes through the 15-years development activity; (i) the exact Larmor motion of impurity ions are computed so that the effects of drifts are automatically taken into account, (ii) the Coulomb collision between impurities and background plasma ions are modelled by the Binary Collision Method which kinetically calculates more precise friction and thermal forces, and (iii) the background plasma transport and impurity transport are computed self-consistently by the coupled calculation with SOL/divertor plasma transport code such as SOLPS-ITER. Although the IMPGYRO transport model has significantly improved from the initial development phase, the modelling improvement of the IMPGYRO has never been described in detail. In this paper, (a) the current W generation/transport model, and (b) the coupling strategy between the SOLPS-ITER and the IMPGYRO are summarized. The new results (c) the check of the prompt re-deposition model of the IMPGYRO, and (d) the further extension of the Coulomb collision modelling of the IMPGYRO towards the neoclassical (NC) transport handling capability has been performed. The effects of the NC transport processes on a simple circular tokamak geometry are compared with the anomalous diffusion by means of the extended IMPGYRO to obtain better understanding of cross-field transport process of W. The results show that the NC transport process may become non-negligible compared to the anomalous diffusion at least in this configuration. Based on these recent improvements, the present version of the IMPGYRO is very useful tool for understanding and prediction of W transport in SOL/divertor regions of fusion devices.

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Simulation study of mixed-impurity seeding with extension of integrated divertor code SONIC

Yamoto S., Hoshino K., Homma Y., Nakano T., Hayashi N.

Plasma Physics and Controlled Fusion 62 （ 4 ） 045006 2020年02月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 07413335

© 2020 IOP Publishing Ltd. Aimed at obtaining key physics that determine the controllability of impurity transport in the scrape-off layer (SOL)/divertor regions, the integrated divertor code SONIC has been further extended to handle three or more impurity species kinetically. The extended SONIC code has been applied to the steady-state high-beta scenario-like plasma of JT-60SA as a testbed. We first performed a Ne transport simulation on the fixed Ar-seeded background plasma. Different radiation power distribution along the magnetic field line was obtained between Ar and Ne. The Ar radiation is strong around the top region of the SOL, which is mainly due to the line radiation of highly charged Ar ions trapped by the thermal force. In contrast, the Ne radiation is strong around the high-field side near the X point, mainly due to the line radiation of Ne7+ trapped by the balance between the thermal force and the frictional force with D+ parallel flow. We performed a parametric survey of Ne seeding rate as a second step. The effects of Ne transport on the plasma are self-consistently computed. The Ne impurities are injected into the plasma with a fixed puff rate of Ar. Even a small Ne seeding rate of 0.02 Pa m3 s-1 results in lower Ar radiation power in the SOL and core edge than in the Ar-only case. This is mainly due to the high D+ parallel flow velocity towards the inner divertor in the Ar + Ne seeding case. The resultant frictional force transports the Ar impurities towards the inner divertor region. When the line radiation of Ne7+ is switched off in the simulation, such high D+ parallel flow cannot be seen. These results suggest that the line radiation of Ne7+ has a key role for the high D+ parallel flow. The results show the possibility of impurity transport control in the SOL by mixed-impurity seeding.

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