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Journal Articles

Transport and confinement physics Chapter 2 of the special issue: on the path to tokamak burning plasma operation

Yoshida, M.*; McDermott, R. M.*; Angioni, C.*; Camenen, Y.*; Citrin, J.*; Jakubowski, M.*; Hughes, J. W.*; Idomura, Yasuhiro; Mantica, P.*; Mariani, A.*; et al.

Nuclear Fusion, 65(3), p.033001_1 - 033001_132, 2025/02

 Times Cited Count:2 Percentile:0.00(Physics, Fluids & Plasmas)

Progress in physics understanding and theoretical model development of plasma transport and confinement in the ITPA Transport and Confinement Topical Group since the publication of the ITER Physics Basis was summarized focusing on the contributions to ITER and burning plasma prediction and control. This paper provides a general and streamlined overview on the advances that were mainly led by the ITPA TC joint experiments and joint activities for the last 15 years. This paper starts with the scientific strategy and scope of the ITPA TC Topical group and overall picture of the major progress, followed by the progress of each research field: particle transport, impurity transport, ion and electron thermal turbulent transport, momentum transport, impact of 3D magnetic fields on transport, confinement mode transitions, global confinement, and reduced transport modeling.

Journal Articles

Effective porosity in groundwater flow analysis for fractured sedimentary rocks; Case studies of the Koetoi and Wakkanai formations in Horonobe, Hokkaido, Japan

Miyakawa, Kazuya; Ishii, Eiichi; Imai, Hisashi*; Hirai, Satoru*; Ono, Hirokazu; Nakata, Kotaro*; Hasegawa, Takuma*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.82 - 95, 2024/12

no abstracts in English

Journal Articles

Full-f gyrokinetic simulations of hydrogen isotope mixing in tokamak plasmas

Idomura, Yasuhiro

Physics of Plasmas, 31(10), p.102504_1 - 102504_10, 2024/10

 Times Cited Count:0 Percentile:0.00(Physics, Fluids & Plasmas)

Hydrogen isotope mixing phenomena in tokamak plasmas are analyzed using global full-f gyrokinetic simulations. Model plasma parameters are chosen based on the hydrogen isotope pellet experiments on JET, in which hydrogen isotope mixing in the time scale of the energy confinement time occurred after injecting deuterium (D) pellets into hydrogen (H) plasmas. Two numerical experiments are conducted using plasma profiles before and after the D pellet injection. In both cases, turbulent fluctuations in the plasma core are characterized by ion temperature gradient driven turbulence, while in the latter case, trapped electron mode turbulence also exists in the outer region. In the former case, the density profile of bulk H ions is kept in a quasi-steady state, and the particle confinement time of bulk H ions is an order of magnitude longer than the energy confinement time. In the latter case, the density profiles of bulk H ions and pellet D ions show transient relaxation in the time scale of the energy confinement time, indicating the fast hydrogen isotope mixing. In the toroidal angular momentum balance, it is found that the hydrogen isotope mixing is driven by the toroidal field stress.

Journal Articles

Free-surface flow simulations with floating objects using lattice Boltzmann method

Watanabe, Seiya*; Kawahara, Jun*; Aoki, Takayuki*; Sugihara, Kenta; Takase, Shinsuke*; Moriguchi, Shuji*; Hashimoto, Hirotada*

Engineering Applications of Computational Fluid Mechanics, 17(1), p.2211143_1 - 2211143_23, 2023/00

 Times Cited Count:7 Percentile:72.05(Engineering, Multidisciplinary)

In tsunami inundations or slope disasters of heavy rain, a lot of floating debris or driftwood logs are included in the flows. The damage to structures from solid body impacts is more severe than the damage from the water pressure. In order to study free-surface flows that include floating debris, developing a high-accurate simulation code of free-surface flows with high performance for large-scale computations is desired. We propose the single-phase free-surface flow model based on the cumulant lattice Boltzmann method coupled with a particle-based rigid body simulation. The discrete element method calculates the contact interaction between solids. An octree-based AMR (Adaptive Mesh Refinement) method is introduced to improve computational accuracy and time-to-solution. High-resolution grids are assigned near the free surfaces and solid boundaries. We conducted two kinds of tsunami flow experiments in the 15 and 70 m water tanks at Hachinohe Institute of Technology and Kobe University to validate the accuracy of the proposed model. The simulation results have shown good agreement with the experiments for the drifting speed, the number of trapped wood pieces, and the stacked angles.

Journal Articles

$$^{178}$$Hg and asymmetric fission of neutron-deficient pre-actinides

Jhingan, A.*; Andreyev, A. N.; 28 of others*

Physical Review C, 106(4), p.044607_1 - 044607_9, 2022/10

 Times Cited Count:6 Percentile:64.05(Physics, Nuclear)

Journal Articles

Study on gas entrainment evaluation method at free liquid surface; Application study of adaptive mesh refinement method on unsteady wake vortex analysis

Alzahrani, H.*; Matsushita, Kentaro; Sakai, Takaaki*; Ezure, Toshiki; Tanaka, Masaaki

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 6 Pages, 2022/10

Development of evaluation method for cover gas entrainment (GE) by vortices generated at free surface in upper plenum of sodium-cooled fast reactor (SFR) is required. An evaluation method by predicting vortices from flow velocity distribution obtained by 3D CFD analysis is developed, and Adaptive Mesh Refinement (AMR) method is examined to improve efficiency of CFD analysis is examined. In this study, mesh refinement with two conditions were examined. The first one is to use negative second invariant of velocity gradient tensor, Q, and the second one is to use pressure gradient condition with Q$$<$$0. As a result of applying AMR method to unsteady vortices system with a flat plate, the mesh near stagnation area around flat plate was refined in the latter condition compared with the former. Transient analyses were performed with refined mesh by AMR method, the result of mesh using the latter condition was closer to the result of all refined mesh with pressure distribution near flat plate.

Journal Articles

Tree cutting approach for domain partitioning on forest-of-octrees-based block-structured static adaptive mesh refinement with lattice Boltzmann method

Hasegawa, Yuta; Aoki, Takayuki*; Kobayashi, Hiromichi*; Idomura, Yasuhiro; Onodera, Naoyuki

Parallel Computing, 108, p.102851_1 - 102851_12, 2021/12

 Times Cited Count:6 Percentile:47.10(Computer Science, Theory & Methods)

The aerodynamics simulation code based on the lattice Boltzmann method (LBM) using forest-of-octrees-based block-structured local mesh refinement (LMR) was implemented, and its performance was evaluated on GPU-based supercomputers. We found that the conventional Space-Filling-Curve-based (SFC) domain partitioning algorithm results in costly halo communication in our aerodynamics simulations. Our new tree cutting approach improved the locality and the topology of the partitioned sub-domains and reduced the communication cost to one-third or one-fourth of the original SFC approach. In the strong scaling test, the code achieved maximum $$times1.82$$ speedup at the performance of 2207 MLUPS (mega- lattice update per second) on 128 GPUs. In the weak scaling test, the code achieved 9620 MLUPS at 128 GPUs with 4.473 billion grid points, while the parallel efficiency was 93.4% from 8 to 128 GPUs.

Journal Articles

AMR-Net: Convolutional neural networks for multi-resolution steady flow prediction

Asahi, Yuichi; Hatayama, Sora*; Shimokawabe, Takashi*; Onodera, Naoyuki; Hasegawa, Yuta; Idomura, Yasuhiro

Proceedings of 2021 IEEE International Conference on Cluster Computing (IEEE Cluster 2021) (Internet), p.686 - 691, 2021/10

 Times Cited Count:3 Percentile:59.95(Computer Science, Hardware & Architecture)

We develop a convolutional neural network model to predict the multi-resolution steady flow. Based on the state-of-the-art image-to-image translation model pix2pixHD, our model can predict the high resolution flow field from the set of patched signed distance functions. By patching the high resolution data, the memory requirements in our model is suppressed compared to pix2pixHD.

Journal Articles

Experimental study on modeling of Pu sorption onto quartz

Hemmi, Ko; Walker, A.*; Yamaguchi, Tetsuji

Radiochimica Acta, 109(7), p.539 - 546, 2021/07

 Times Cited Count:1 Percentile:0.00(Chemistry, Inorganic & Nuclear)

Plutonium(IV) sorption onto quartz in carbonate solutions was systematically investigated under anaerobic conditions to analyze the sorption behaviors of Pu(IV) with a non-electrostatic model (NEM). Pu(IV) sorption data was obtained from batch sorption experiments as a function of pH and carbonate concentration. The Pu(IV) sorption onto quartz showed similar tendencies to Th(IV), which is considered to be chemically analogous as a tetravalent actinoid. The distribution coefficient, ${it K}$d, of Pu(IV) onto quartz showed inverse proportionality to the square of the total carbonate concentration under the investigated pH conditions of 8 to 11. The modeling study, however, revealed a Th(IV) sorption model, which is $$equiv$$SOTh(OH)$$_{4}$$$$^{-}$$ and $$equiv$$SOThOH(CO$$_{3}$$)$$_{2}$$$$^{2-}$$, could not be applied to simulate the Pu(IV) sorption onto quartz. It was inferred that the electrostatic repulsion between negatively charged ligands limited the formation of $$equiv$$SOM(OH)$$_{4}$$$$^{-}$$ and $$equiv$$SOMOH(CO$$_{3}$$)$$_{2}$$$$^{2-}$$ for Pu(IV) with smaller ionic radii than Th(IV). The Pu(IV) sorption model was developed as $$equiv$$SOPu(OH)$$_{3}$$ and $$equiv$$SOPu(OH)$$_{4}$$$$^{-}$$. In addition, data of Pu(IV) sorption onto muscovite was obtained in order to be compared with data for quartz.

Journal Articles

Analysis of feedback control of magnetic islands via rotational field based on Rutherford model

Uenaga, Issei; Furukawa, Masaru*

Physics of Plasmas, 27(9), p.092501_1 - 092501_11, 2020/09

 Times Cited Count:0 Percentile:0.00(Physics, Fluids & Plasmas)

This work uses the Rutherford model for a cylindrical plasma to study the dynamics of magnetic islands under external magnetic perturbations, including both applied rotational magnetic fields and static error magnetic fields. The results show that, in an unstable tearing situation, magnetic islands are completely suppressed by modulating the frequency of the externally applied rotational magnetic field to maintain the phase of the combined external magnetic field to be opposite (or nearly opposite) that of the magnetic islands. The frequency is modulated by using a proportional controller in the simulation, where the frequency of the rotational field is determined by using the island rotation frequency "measured" in the simulation.

JAEA Reports

Study on release behavior of radioiodine from fuel solution under criticality accident condition

Tashiro, Shinsuke; Abe, Hitoshi

JAEA-Technology 2015-044, 20 Pages, 2016/03

JAEA-Technology-2015-044.pdf:1.26MB

In order to estimate public dose under a criticality accident in fuel solution of a fuel reprocessing plant, release behavior of radioiodine from the fuel solution to atmosphere is very important. In this report, time evolution of $$^{133}$$I concentration in gas phase of TRACY core tank was measured until the concentration in the solution decreased. Furthermore, cumulative release ratio (CRR) and release rate (RR) from the solution to the atmosphere of radioiodine were evaluated by applying previously-reported evaluation model. As a result, for the case of short transient criticality, RR of $$^{133}$$I became maximum at 1 hour later from the ending and almost constant after 8 hour later. Furthermore, relationship of each elapsed time between total fission number and release rate of $$^{133}$$I could be derived. On the other hand, for the case of long criticality excursion, such as JCO criticality accident, the CRR and RR of radioiodine increased monotonously with time.

Journal Articles

Evaluation of tritium confinement performance of alumina and zirconium for tritium production in a high-temperature gas-cooled reactor for fusion reactors

Katayama, Kazunari*; Ushida, Hiroki*; Matsuura, Hideaki*; Fukada, Satoshi*; Goto, Minoru; Nakagawa, Shigeaki

Fusion Science and Technology, 68(3), p.662 - 668, 2015/10

 Times Cited Count:18 Percentile:78.44(Nuclear Science & Technology)

Tritium production utilizing nuclear reactions by neutron and lithium in a high-temperature gas-cooled reactor is attractive for development of a fusion reactor. From viewpoints of tritium safety and production efficiency, tritium confinement technique is an important issue. It is known that alumina has high resistance for gas permeation. In this study, hydrogen permeation experiments in commercial alumina tubes were conducted and hydrogen permeability, diffusivity and solubility was evaluated. By using obtained data, tritium permeation behavior from an Al$$_{2}$$O$$_{3}$$-coated Li-compound particle was simulated. Additionally, by using literature data for hydrogen behavior in zirconium, an effect of Zr incorporation into an Al$$_{2}$$O$$_{3}$$ coating on tritium permeation was discussed. It was indicated that the majority of produced tritium was released through the Al$$_{2}$$O$$_{3}$$ coating above 500$$^{circ}$$C. However, it is expected that total tritium leak is suppressed to below 0.67% of total tritium produced at 500$$^{circ}$$C by incorporating Zr fine particles into the inside of Al$$_{2}$$O$$_{3}$$ coating.

Journal Articles

Confinement degradation with beta for ELMy $$H$$-mode plasmas in JT-60U tokamak

Urano, Hajime; Takizuka, Tomonori; Takenaga, Hidenobu; Oyama, Naoyuki; Miura, Yukitoshi; Kamada, Yutaka

Nuclear Fusion, 46(8), p.781 - 787, 2006/08

 Times Cited Count:23 Percentile:58.86(Physics, Fluids & Plasmas)

The degradation of energy confinement with increased toroidal beta $$beta_mathrm{T}$$ was shown by the non-dimensional analysis in JT-60U. The dependence of the energy confinement on $$beta_mathrm{T}$$ was examined by both the JT-60U ELMy $textit{H}$-mode confinement database and the dedicated experiment on a single $$beta_mathrm{T}$$ scan while $$rho_mathrm{T}^ast$$ and $$nu^ast$$ were kept fixed as well as the other magnetic geometrical parameters. In both cases, the degradation of energy confinement with increasing $$beta_mathrm{T}$$ was observed, satisfying the relation of $$B_mathrm{T} tau_mathrm{E} propto beta_mathrm{T}^{-(0.6-0.7)}$$. This dependence is a little weaker than that predicted by the IPB98(y,2) scaling. The fusion power production rate was estimated to increase in proportion to $$beta_mathrm{T}^{0.3-0.4} B_mathrm{T}$$.

Journal Articles

Origin of the various beta dependences of ELMy H-mode confinement properties

Takizuka, Tomonori; Urano, Hajime; Takenaga, Hidenobu; Oyama, Naoyuki

Plasma Physics and Controlled Fusion, 48(6), p.799 - 806, 2006/06

 Times Cited Count:15 Percentile:44.90(Physics, Fluids & Plasmas)

Dependence of the ELMy H-mode confinement on the beta has been investigated for a long time, but a common conclusion has not yet been obtained.The IPB98(y,2) scaling shows a strong degradation with beta, while DIII-D and JET experiments exhibited the absence of the beta degradation. Recent JT-60U experiment demonstrated that the strong beta degradation really exists for the ELMy H-mode. In the present paper, we analyze the JT-60U ELMy H-mode confinement database and confirm the strong power degradation of the confinement time, which corresponds to the strong beta degradation consistent with the above result. We analyze also the ITPA H-mode confinement database in detail. How the beta dependence of the confinement time is changed by the externally given parameters, such as the shape parameters, are investigated.

Journal Articles

Design study of national centralized tokamak facility for the demonstration of steady state high-$$beta$$ plasma operation

Tamai, Hiroshi; Akiba, Masato; Azechi, Hiroshi*; Fujita, Takaaki; Hamamatsu, Kiyotaka; Hashizume, Hidetoshi*; Hayashi, Nobuhiko; Horiike, Hiroshi*; Hosogane, Nobuyuki; Ichimura, Makoto*; et al.

Nuclear Fusion, 45(12), p.1676 - 1683, 2005/12

 Times Cited Count:15 Percentile:44.69(Physics, Fluids & Plasmas)

Design studies are shown on the National Centralized Tokamak facility. The machine design is carried out to investigate the capability for the flexibility in aspect ratio and shape controllability for the demonstration of the high-beta steady state operation with nation-wide collaboration, in parallel with ITER towards DEMO. Two designs are proposed and assessed with respect to the physics requirements such as confinement, stability, current drive, divertor, and energetic particle confinement. The operation range in the aspect ratio and the plasma shape is widely enhanced in consistent with the sufficient divertor pumping. Evaluations of the plasma performance towards the determination of machine design are presented.

Journal Articles

Small ELM regimes with good confinement on JET and comparison to those on ASDEX Upgrade, Alcator C-mod and JT-60U

Stober, J.*; Lomas, P. J.*; Saibene, G.*; Andrew, Y.*; Belo, P.*; Conway, G. D.*; Herrmann, A.*; Horton, L. D.*; Kempenaars, M.*; Koslowski, H.-R.*; et al.

Nuclear Fusion, 45(11), p.1213 - 1223, 2005/11

 Times Cited Count:46 Percentile:77.75(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Conference summary; Progress in experiments on confinement, plasma-material interactions and innovative confinement concepts

Ninomiya, Hiromasa

Nuclear Fusion, 45(10), p.S13 - S31, 2005/10

 Times Cited Count:0 Percentile:0.00(Physics, Fluids & Plasmas)

This paper summarizes the results presented at the 20th IAEA Fusion Energy Conference 2004 in the sessions of confinement, plasma-wall interaction and innovative confinement concept. The highlights of the presentations are as follows. Long pulse operation with high beta and high bootstrap fraction much longer than the current diffusion time has been achieved. The discharge scenario optimization and its extrapolation towards ITER have progressed remarkably. Significant progress has been made in understanding of global confinement and transport physics.

Journal Articles

Scaling of the energy confinement time with $$beta$$ and collisionality approaching ITER conditions

Cordey, J. G.*; Thomsen, K.*; Chudnovskiy, A.*; Kardaun, O. J. W. F.*; Takizuka, Tomonori; Snipes, J. A.*; Greenwald, M.*; Sugiyama, L.*; Ryter, F.*; Kus, A.*; et al.

Nuclear Fusion, 45(9), p.1078 - 1084, 2005/09

 Times Cited Count:53 Percentile:82.21(Physics, Fluids & Plasmas)

The condition of the latest version of the ELMy H-mode database has been re-examined. It is shown that there is bias in the ordinary least squares regression for some of the variables. To address these shortcomings three different techniques are employed: (a)principal component regression, (b)an error in variables technique and (c)the selection of a better conditioned dataset with fewer variables. Scalings in terms of the dimensionless physics valiables, as well as the standard set of engineering variables, are derived. The new scalings give a very similar performance for existing scalings for ITER at the standard beta, but a much improvement performance at higher beta.

Journal Articles

Intelligible seminor on fusion reactors, 1; Introduction to fusion reactors

Ueda, Yoshio*; Inoue, Takashi; Kurihara, Kenichi

Nihon Genshiryoku Gakkai-Shi, 46(12), p.845 - 852, 2004/12

no abstracts in English

Journal Articles

Pedestal characteristics in JFT-2M HRS H-mode plasma

Kamiya, Kensaku; Oyama, Naoyuki; Miura, Yukitoshi; Hubbard, A. E.*

Plasma Physics and Controlled Fusion, 46(11), p.1745 - 1755, 2004/11

 Times Cited Count:13 Percentile:39.20(Physics, Fluids & Plasmas)

Recent experiments in the JFT-2M tokamak have concentrated on the studies of the access condition for the H-mode operation without any large ELMs, namely High Recycling Steady (HRS) H-mode regime in terms of the pedestal parameters. The HRS regime is more likely at the higher edge density and lower edge temperature, while the ELMy H-mode having large ELMs appears at the lower edge density and higher edge temperature. It is found that the ELMy/HRS operational boundary occurs at the normalized electron collisionality of $$nu$$*$$_{e}$$$$sim$$1 in the plasma edge region, depending slightly on q$$_{95}$$. A key feature of the HRS H-mode is the presence of the coherent magnetic fluctuations in the frequency range of the order of 10-100 kHz. It is suggested that the edge MHD activities may keep an edge pressure below a certain level needed to induce a large ELM.

112 (Records 1-20 displayed on this page)