研究者詳細 - 星野　一生

論文 - 星野　一生

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Deep learning model for predicting the spatial distribution of binding energy from atomic configurations

S. Sato H. Nakamura, C. Takahashi, K. Sawada, K. Hoshino, M. Kobayashi, M. Hasuo

Japanese Journal of Applied Physics 2024年08月

研究論文（学術雑誌）, 共著, 査読有り

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Numerical study of the plasma meniscus shape and beam optics in RF negative ion sources

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

Journal of Instrumentation 19 （ 4 ） C04031 2024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

In order to extract intense ion beams with good beam optics from hydrogen negative ion sources, it is important to control the shape of the plasma meniscus (i.e. beam emission surface). Recently, it is suggested experimentally that the degradation of beam optics in the RF negative ion sources may be due to the fluctuation of the distance d eff between the meniscus and the extraction grid caused by the fluctuation of the plasma density np . The purpose of this study is to make clear the dependence of d eff on np in the presence of a large amount of surface produced H- ions in order to understand such fluctuation of beam optics in RF sources For the purpose, 3D electrostatic PIC simulation was conducted taking the bulk plasma density as a parameter, investigating the extraction region of a H- ion source. A large amount of the surface H- production on the PG has been taken into account under the assumption that the H- production rate is proportional to the bulk plasma density. The result shows that the effective distance d eff is proportional to np-1/2 even for a large amount of surface H- production. This dependence suggests that the bulk plasma density np is the key parameters to control d eff and the resultant beam optics extracted from the negative ion source.

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Hamiltonian simulation using the quantum singular-value transformation: Complexity analysis and application to the linearized Vlasov-Poisson equation

Toyoizumi K., Yamamoto N., Hoshino K.

Physical Review A 109 （ 1 ） 01243 2024年01月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 24699926

Quantum computing can be used to speed up the simulation time (more precisely, the number of queries of the algorithm) for physical systems; one such promising approach is the Hamiltonian simulation (HS) algorithm. Recently, it was proven that the quantum singular-value transformation (QSVT) achieves the minimum simulation time for HS. An important subroutine of the QSVT-based HS algorithm is the amplitude amplification operation, which can be realized via the oblivious amplitude amplification or the fixed-point amplitude amplification in the QSVT framework. In this work we execute a detailed analysis of the error and number of queries of the QSVT-based HS and show that the oblivious method is better than the fixed-point one in the sense of simulation time. Based on this finding, we apply the QSVT-based HS to the one-dimensional linearized Vlasov-Poisson equation and demonstrate that the linear Landau damping can be successfully simulated.

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Spatial Distribution Analyses of Axially Long Plasmas under a Multi-Cusp Magnetic Field Using a Kinetic Particle Simulation Code KEIO-MARC

Nishimura R., Seino T., Yoshimura K., Takahashi H., Matsuyama A., Hoshino K., Oishi T., Tobita K.

Plasma （Plasma) 7 （ 1 ） 64 - 75 2024年01月

研究論文（学術雑誌）, 共著, 査読有り

To realize the development of a long plasma source with a uniform electron density distribution in the axial direction, the spatial distribution of plasma under a multi-cusp magnetic field was analyzed using a KEIO-MARC code. Considering a cylindrical plasma source with an axial length of 3000 mm and a cross-sectional diameter of 100 mm, in which the filament electrode was the electron source, the electron density distribution was calculated using the residual magnetic flux density, Bres, and the number of permanent magnets installed at different locations surrounding the device, Nmag, as design parameters. The results show that both Bres and Nmag improved the uniformity of the electron density distribution in the axial direction. The maximum axial electron density decreased with increasing Nmag and increased with increasing Bres. These trends can be explained by considering the nature of the multi-cusp field, where particles are mainly confined to the field-free region (FFR) near the center of the plasma column, and the loss of particles due to radial particle transport. The use of multiple filaments at intervals shorter than the plasma decay length dramatically improved axial uniformity. To further improve axial uniformity, the filament length and FFR must be properly set so that electrons are emitted inside the FFR.

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Effect of Large-Angle Scattering on Particle Transport and Heat Flux in Advanced Divertor Magnetic Field Configurations

Umezaki D., Matsuura H., Hoshino K.

Plasma and Fusion Research （一般社団法人プラズマ・核融合学会) 19 （ 0 ） 1403003 - 1403003 2024年01月

研究論文（学術雑誌）, 共著, 査読有り

Divertor heat loads are one of the most significant issues affecting fusion reactors. Atomic processes play a crucial role in reduction of the divertor heat load. Notably, elastic scattering between ions and neutral particles can be characterized as large-angle scattering. A large fraction of ion energy is transferred to neutral particles, and the ion direction can be significantly changed by a single large-angle scattering event. In abundant neutral particle regions such as divertor plasmas, the large-angle elastic scattering results in additional ion transport perpendicular to magnetic field lines. Effect of the additional ion transport is expected to be significant at low magnetic field strength and long Larmor radii, such as in a case of advanced divertors (e.g., Super-X and Snowflake divertors). In this study, we investigated the effect of the large-angle elastic scattering at low magnetic field strength and long divertor legs with reference to advanced divertor configurations using an orbital calculation. The large-angle elastic scattering transport is seen to cause a spread in density profiles and a reduction of heat flux. The results of this study show that for the short (long) leg divertor configuration like JT-60U (advanced divertor), the peak heat flux is reduced by around 15% (21%) when the magnetic field strength is 0.5 T in comparison to the model that assumes no guiding center movement due to the elastic scattering. It is also shown that the assumption of isotropic elastic scattering with neutral particles leads to excessive suppression of ion flows.

SOL impurity transport analysis with SONIC code with a kinetic effect on a thermal force transport model in JT-60U

Kobayashi M., Yamoto S., Hoshino K., Asakura N., Homma Y., Aiba N., Nakano T., Sano R., Kawamura G., Hayashi Y.

Contributions to Plasma Physics （Contributions to Plasma Physics) 2024年

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

The latest version of the SONIC code with the extended thermal force model that is capable to treat collisionality dependence of the force has been applied to the interpretative simulation of L-mode discharge of JT-60 U to investigate the impact of kinetic correction of the thermal force on the scrape-off layer (SOL) plasma properties. As a first attempt, we have selected an L-mode attached discharge #39090 (Ip = 1.6 MA, Bt = 3.1 T, and PNBI = 4.5 MW), where (Formula presented.) = 2.08 × 1019 m−3, (Formula presented.) = 0.392 with deuterium plasmas. It has been found that the peak values of SOL impurity density are reduced by a factor of 2, with the kinetic correction, because the thermal force is reduced by the low collisionality of SOL plasma between the X-point and the (inner and outer) midplane. On the other hand, the profiles near the divertor plates are unaffected by the kinetic correction due to the highly collisional condition. The kinetic correction is found more pronounced for the higher charge states impurity due to the charge dependence of the parallel impurity force balance. Overall effects due to the kinetic correction on the total impurity radiation and the divertor heat load are confirmed to be a few % in the present discharge condition of JT-60U.

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Estimation of impact of non-local ion heat flux model on transport simulation for DEMO-relevant scrape-off layer plasma

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

Contributions to Plasma Physics 2024年

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

In a fusion DEMOnstration reactor (DEMO)-relevant scrape-off layer plasma (SOL), whose collisionality is lower than in the SOLs of present-day tokamaks, kinetic effects are predicted to reduce the plasma heat conductivity along the magnetic field below the value obtained with the classical Spitzer–Harm model. As a part of ongoing efforts to improve the predictive capability of SOL heat transport calculations, we have implemented the non-local heat flux model proposed by [Luciani, Mora and Virmont, Phys. Rev. Lett. 51 (1983) 1664–1667] (here referred to as the LMV model) in the integrated SOL–divertor simulation code SONIC in order to account for the kinetic effect on the heat conduction due to the parallel streaming of rapidly moving particles. Our transport simulations for the Japanese demonstration tokamak reactor concept, JA DEMO, show that the LMV model yields a significantly reduced ion parallel conductive heat flux density both on the low- and high-field side of the upstream SOL. The heat flux obtained with the LMV model seems to be consistent with earlier kinetic simulations of tokamak ion transport. As a consequence of the reduced heat flux, a significant increase in the ion temperature and a decrease in the density have also been found over a broad area of the upstream SOL.

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First results of multi-fluid modeling of detached hydrogen plasmas in a linear plasma device using fluid code LINDA-NU

Sugiura K., Ido T., Tanaka H., Natsume H., Masuda S., Hoshino K., Sawada K., Ohno N.

Contributions to Plasma Physics （Contributions to Plasma Physics) 2024年

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

In order to simulate hydrogen (H) plasma in the linear plasma device NAGDIS-II, we have modified the fluid code LINDA-NU to allow the simultaneous calculation of multiple ion species consisting of hydrogen atomic ions ((Formula presented.)) and molecular ions ((Formula presented.)). In this simulation, H and (Formula presented.) neutrals are assumed to be uniformly distributed in space in order to obtain initial qualitative results. The fraction of (Formula presented.) ions increases as the (Formula presented.) molecular density increases, and the recombination process between (Formula presented.) and electrons is observed to reduce the particle flux to the target plate. With an increase in H density, the electron density increases due to the decrease in ion flow velocity due to the change exchange process, and the electron temperature decreases to less than 1 eV, leading to the detached plasma formation attributed to the electron-ion recombination process.

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Simple 3D PIC Analysis for Beam Phase Space Oscillation in RF Driven Negative Hydrogen Ion Source

Shibata T., Shinto K., Nakano H., Hoshino K., Miyamoto K., Ohkoshi K., Nanmo K., Ikegami K., Kawai I., Oguri H., Wada M.

Journal of Physics: Conference Series （Journal of Physics: Conference Series) 2743 （ 1 ） 012007 2024年

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

Temporal oscillation of the negative hydrogen ion (H-) beam in the Radio Frequency (RF) ion source is investigated by a simple 3D3V Particle-In-Cell (PIC) model. The model solves electron, proton, and H- transport processes in the extraction region. The calculation domain is from the vicinity of the beam aperture to the ground electrode. To understand the relation between the plasma density oscillation and the extracted H- beam characteristics, the input electron and proton fluxes from the driver region are varied parametrically with the fundamental J-PARC RF frequency (2 MHz). The numerical results give an idea of the main physical processes between the oscillations of the plasma parameters and the extracted H- ion trajectories depending on the plasma meniscus shape in the different RF phases.

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Effect of elastic scattering between ions and neutral particles on ion transport perpendicular to magnetic fields in divertor plasmas

Umezaki D., Matsuura H., Hoshino K.

Contributions to Plasma Physics 64 （ 1 ） e202300064 2023年09月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 08631042

In divertor plasmas, atomic processes play a significant role in reducing the divertor heat load. In particular, the elastic scattering between ions and neutral particles can be characterized as a large-angle scattering; this is in contrast with Coulomb scattering, which is dominated by small-angle scattering. In a large-angle scattering, a large fraction of the ion energy is transferred to the neutral particle, and the particle flight direction can be changed significantly. This process can generate additional particle transport perpendicular to magnetic field lines and affect plasma density profile in neutral-rich divertor regions. However, in most edge plasma simulation codes, the elastic scattering with neutral particles is not taken into account in the direction perpendicular to the magnetic field lines. In this study, we performed a 2D orbital calculation without other drifts such as diamagnetic and E × B drifts to assess the effect of the elastic scattering on the density profile. The peak density is found to be decreased by 11.1 (6.3)% compared with the model that ignores the transport due to the elastic scattering, even at 3.0 (5.0) T magnetic field similar to that of the JT-60SA (JA DEMO reactor) class. In addition, the ion transport can be expressed as a diffusion model by integrating the differential cross section over the large-angle scattering range (Formula presented.). The proposed method may be easily introduced into any integrated codes to consider the elastic scattering.

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The development of a zero-dimensional collisional-radiative model for interpreting plasma emission in low temperature divertor plasmas in tokamaks

Fox-Widdows E., Bowden M.D., Hoshino K., Hatayama A., Osawa R., Tsubotani Y.

Frontiers in Physics 11 1154185 2023年07月

研究論文（学術雑誌）, 共著, 査読有り

Collisional-radiative models are commonly used to analyse atomic and molecular processes in low temperature plasmas by determining the distribution functions of excited states as functions of various plasma parameters. This paper outlines the improvements to a zero-dimensional collisional-radiative model, developed at Keio University, for purposes relevant to the analysis of emission measurements in low temperature hydrogen plasmas. The extension of this 0D model centres on the inclusion of additional molecular species and reactions, a calculation of emission intensity in order to directly compare with experimental work, and the addition of a simple wall model to allow for a deeper understanding of recycling of atoms and molecules in low temperature plasmas close to plasma facing components in fusion machines. Results from the improved model are then compared with both an existing CR model for benchmarking and experimental emission spectroscopy data from an inductively-coupled plasma device at the University of Liverpool. These results show how the developments to the model have increased the relevance to experimental plasmas, such as those in the power exhaust regions of fusion machines, with the ratio of the Hβ/Hα line intensities outputted from the improved CR model mirroring more closely the emission measured experimentally in the ICP device.

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Transient analysis of high-Z impurity screening by additional injection of low-Z impurity using integrated divertor code SONIC

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

Nuclear Fusion （Nuclear Fusion) 63 （ 7 ） 076019 2023年06月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 00295515

The dynamics of the screening effect of Ar impurity by the injection of additional Ne has been studied through time-dependent analysis with the integrated divertor code SONIC. In the preceding study (Yamoto et al 2020 Plasma Phys. Control. Fusion 62 045006), the predictive simulation of JT-60SA plasma by SONIC has shown that the injection of additional Ne into Ar-seeded plasma results in lower Ar density and radiation power in the SOL and core edge than in the Ar-only seeded case. The results have demonstrated that the mixed impurity seeding of Ar and Ne may be advantageous for maintaining a high core plasma performance with a low divertor heat load. It was found that the friction force induced by the high D+ flow in the SOL towards the inner divertor (ID) region in the Ar + Ne seeded case pushes Ar impurities to the ID. However, the dynamics of D+ flow acceleration cannot be interpreted in the previous study because SONIC was a steady state code. In this study, we have developed the time-dependent version of SONIC and applied it to the transient analysis of the injection of additional Ne into Ar-seeded plasma in JT-60SA. When additional Ne is injected, Ne ions stay in the ID plasma near the X-point. As a result, the Ne radiation power increases near the X-point. The electron pressure then decreases due to the radiation cooling and the D+ flow is accelerated by the electron pressure gradient. The ion pressure also decreases due to the convection by the accelerated D+ flow by electron pressure gradient. The resulting ion pressure gradient further accelerates the D+ flow velocity towards the ID. The results suggest that both the high-performance core plasma and the low divertor heat load can be achieved by the Ar + Ne mixed impurity seeding.

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Study of plasma meniscus including surface produce negative ions by using PIC-MCC simulation

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

Journal of Instrumentation 18 （ 6 ） C06014 2023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

In general, a quality of negative ion beam optics is determined by the shape of the plasma meniscus, which is an ion emitting surface. In this study, the key parameters to control the plasma meniscus and relevant physical structure in the electronegative plasma including the surface produced H- ions is investigated by using PIC-MCC simulation. The region from the source plasma up to the accelerator is modeled for a single aperture, and thus, the plasma meniscus can be obtained self-consistently. Parameter survey for the net flux of surface produced H- ion is conducted by varing the numbers of the surface produced H- ion super-particles per timestep in order to investigate the effcet of the electronegativity, that is, the ratio of the negative ion density to the electron density. It is shown that the effective distance d eff, between the plasma meniscus and the extraction grid depends on the electronegativity as well as the plasma density. Especially, the effective distance d eff, decreases with the increase of the electronegativity under the constant plasma density, which means that the shape of the plasma meniscus becomes flat or convex rather than concave. Moreover, it is also verified that the electronegativity affects the H- ion trajectories extracted from near the edge of plasma meniscus through the shape of plasma meniscus.

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Recent progress of plasma exhaust concepts and divertor designs for tokamak DEMO reactors

Asakura N., Hoshino K., Kakudate S., Subba F., You J.H., Wiesen S., Rognlien T.D., Ding R., Kwon S.

Nuclear Materials and Energy 35 101446 2023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

The power exhaust concept and an appropriate divertor design are common critical issues for tokamak DEMO design activities which have been carried out in Europe, Japan, China, Korea and the USA. Conventional divertor concepts and power exhaust studies for recent DEMO designs (Pfusion = 1 – 2 GW, Rp = 7 – 9 m) are reviewed from the viewpoints of the plasma physics issues and the divertor engineering design. Radiative cooling is a common approach for the power fusion scenario. Requirements on the main plasma radiation fraction (fradmain = Pradmain/Pheat) and the plasma performance constrain the divertor design concept. Different challenges contribute to optimizing the future DEMO designs: for example, (i) increasing the main plasma radiation fraction for ITER-level Psep/Rp designs and simplifying the divertor geometry, and (ii) extending ITER divertor geometry with increasing divertor radiation (Praddiv) for larger Psep/Rp ≥ 25MWm−1 designs. Power exhaust simulations with large Psep = 150 – 300 MW have been performed using integrated divertor codes considering an ITER-based divertor geometry with longer leg length (1.6 – 1.7 m), as in a common baseline design. Geometry effects (ITER like geometry or more open one without baffle) on the plasma detachment profile and the required divertor radiation fraction (fraddiv = Praddiv/Psep) were key aspects of these studies. All simulations showed that the divertor plasma detachment were extended widely across the target plate with a reduction in the peak heat load of qtarget ≤ 10 MWm−2 for the large fraddiv = 0.7 – 0.8, while the peak qtarget location and value were noticeably different in the partially detached divertor. Simulation results also demonstrated that radial diffusion coefficients of the heat and particle fluxes were critical parameters for DEMO divertor design, and that effects of plasma drifts on outboard-enhanced asymmetry of the heat flux, suggested the need for longer divertor leg to ensure the existence of a detached divertor operation with qtarget ≤ 10 MWm−2. Integrated design of the water cooled divertor target, cassette body (CB) and cooling pipe routing has been developed for each DEMO concept, based on the ITER-like tungsten monoblock (W-MB) with Cu-alloy cooling pipes. Engineering design adequate under higher neutron irradiation condition was required. Therefore, inlet coolant temperature (Tcool) was increased. In current designs, it still shows a large potential variation between 70 °C and 200 °C. The influence of thermal softening on the Cu-alloy (CuCrZr) pipe was fostered near the strike-point when the high qtarget of ∼10 MWm−2 was studied. Improved technologies for high heat flux components based on the ITER W-MB unit have been developed for EU-DEMO. Different coolant conditions (low- and high-Tcool) were provided for Cu-alloy and reduced activation ferritic martensitic (RAFM) steel heat sink units, respectively. The high-Tcool coolant was also considered for the CB and supporting structures. Appropriate conditions for the high-Tcool coolant, i.e. 180 °C/ 5 MPa (EU-DEMO) and 290 °C/ 15 MPa (JA-DEMO, CFETR and K-DEMO), will be determined in the future optimizations of the divertor and DEMO design.

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Effect of Surface Produced H̄ Ion on the Plasma Meniscus in Negative Hydrogen Ion Sources

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

Plasma and Fusion Research （一般社団法人プラズマ・核融合学会) 18 （ 0 ） 1401008 - 1401008 2023年03月

研究論文（学術雑誌）, 共著, 査読有り

To extract intense ion beams with good beam optics from ion sources, controlling the distance deff between the plasma meniscus (i.e., beam emission surface) and the beam extraction grid is important. This study conducts a novel investigation into the dependence of the effective distance deff on the amount of surface H̄ production SH-. For this purpose, a 3D PIC (three dimensional Particle-in-Cell) simulation is conducted to obtain a model geometry of the extraction region for a H̄ ion source with SH- as a parameter. Based on results, deff significantly depends on SH- and the H̄-electron density ratio (α = nH̄=ne) in front of the extraction aperture for the same plasma density; as SH- increases, deff decreases. The results suggest that SH- is critical for controlling deff and the resultant beam optics extracted from the negative ion source

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.

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