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Journal Articles

Development of a multiphase particle method for melt-jet breakup behavior of molten core in severe accident

Wang, Z.; Iwasawa, Yuzuru; Sugiyama, Tomoyuki

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 12 Pages, 2020/08

Journal Articles

Kinetic modelling of divertor fluxes during ELMs in ITER

Hosokawa, Masanari*; Loarte, A.*; Huijsmans, G.*; Takizuka, Tomonori*; Hayashi, Nobuhiko

Europhysics Conference Abstracts (Internet), 38F, p.P5.003_1 - P5.003_4, 2014/06

Journal Articles

Particle simulation of the transient behavior of one-dimensional SOL-divertor plasmas after an ELM crash

Takizuka, Tomonori; Hosokawa, Masanari*

Contributions to Plasma Physics, 46(7-9), p.698 - 703, 2006/09

 Times Cited Count:13 Percentile:42.6(Physics, Fluids & Plasmas)

Enhanced heat and particle fluxes to the divertor plates after an ELM crash in H-mode plasmas are the crucial issues for the tokamak reactor operation. Kinetic effect in the transient behaviour of SOL-divertor plasmas for this case is not yet well known. We investigate above problems with an advanced particle simulation code, PARASOL. Dependence of the particle and heat propagations on the collisionality is studied systematically. Effect of the particle recycling is also studied.

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:21 Percentile:58.44(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

Thermal properties of redeposition layers in the JT-60U divertor region

Ishimoto, Yuki; Goto, Yoshitaka*; Arai, Takashi; Masaki, Kei; Miya, Naoyuki; Oyama, Naoyuki; Asakura, Nobuyuki

Journal of Nuclear Materials, 350(3), p.301 - 309, 2006/05

 Times Cited Count:21 Percentile:80.79(Materials Science, Multidisciplinary)

Thermal properties of the redeposition layer on the inner plate of the W-shaped divertor of JT-60U have been measured with laser flash method for the first time so as to estimate transient heat loads onto the divertor. Measurement of a redeposition layer sample of more than 200 m thick showed following results: (1) the bulk density of the redeposition layer is about half of that of carbon fiber composite material; (2) the specific heat of the layer is roughly equal to that of the isotropic graphite; (3) the thermal conductivity of the redeposition layer is two orders of magnitude smaller than that of the carbon fiber composite. The difference between the divertor heat loads and the loss of the plasma stored energy becomes smaller taking account of thermal properties of the redeposition layer on the inner divertor, whereas estimated heat loads due to the ELMs is still larger than the loss. This is probably caused by the poloidal distribution of the thermal properties and heat flux asymmetry inherent in the device.

Journal Articles

Observations of the collapse and recovery of the temperature pedestal using diagnostics with the fast temporal resolution in JT-60U

Yoshida, Maiko; Kobayashi, Shinji*; Urano, Hajime; Oyama, Naoyuki; Koide, Yoshihiko; Sakamoto, Yoshiteru; Takenaga, Hidenobu; Kamada, Yutaka; JT-60 Team

Plasma Physics and Controlled Fusion, 48(5A), p.A209 - A215, 2006/05

 Times Cited Count:11 Percentile:37.64(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Impact of the edge pedestal characteristics on the integrated performance in advanced tokamak operation modes in JT-60U

Kamada, Yutaka; Oyama, Naoyuki; Ide, Shunsuke; Sakamoto, Yoshiteru; Isayama, Akihiko; Fujita, Takaaki; Urano, Hajime; Suzuki, Takahiro; Yoshida, Maiko

Plasma Physics and Controlled Fusion, 48(5A), p.A419 - A427, 2006/05

 Times Cited Count:16 Percentile:49.31(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Pedestal conditions for small ELM regimes in tokamaks

Oyama, Naoyuki; Gohil, P.*; Horton, L. D.*; Hubbard, A. E.*; Hughes, J. W.*; Kamada, Yutaka; Kamiya, Kensaku; Leonard, A. W.*; Loarte, A.*; Maingi, R.*; et al.

Plasma Physics and Controlled Fusion, 48(5A), p.A171 - A181, 2006/05

 Times Cited Count:77 Percentile:91.99(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Characterization of Type-I ELMs in tangential co-, balanced- and counter-plus perpendicular NBI heated plasmas on JT-60U

Kamiya, Kensaku; Urano, Hajime; Koide, Yoshihiko; Takizuka, Tomonori; Oyama, Naoyuki; Kamada, Yutaka; JT-60 Team

Plasma Physics and Controlled Fusion, 48(5A), p.A131 - A139, 2006/05

 Times Cited Count:22 Percentile:59.84(Physics, Fluids & Plasmas)

Effects of plasma rotation and ripple loss on the Type-I ELMs have systematically studied in the JT-60U tokamak, scanning combinations of NBI at the three kinds of plasma volumes. New findings on the Type-I ELMs confirm to be smaller ELM energy loss per pedestal stored energy, DWELM/Wped, and faster ELM frequency, fELM, in the counter-NBI than co-NBI, keeping the power of ELM, PELM, per heating power crossing the separatrix, PSEP, constant. Balanced-NBI case is also intermediate between co- and counter-NBI. In addition, the product of PELM/PSEP decreases according to increase in the plasma volume, suggesting an increase in the inter-ELM transport due mainly to an enhancement in the ripple loss of fast ion.

Journal Articles

Characterization of coherent magnetic fluctuations in JFT-2M high recycling steady high-confinement mode plasmas

Kamiya, Kensaku; Oyama, Naoyuki; Ido, Takeshi*; Bakhtiari, M.*; JFT-2M Group

Physics of Plasmas, 13(3), p.032507_1 - 032507_9, 2006/03

 Times Cited Count:13 Percentile:42.6(Physics, Fluids & Plasmas)

Accompanying the HRS H-mode transition, the coherent magnetic fluctuations in the frequency range of the order of 10-100 kHz with significant variation are seen on the magnetic probes at the vessel wall. Above all, two types of edge MHD activities, which have associated toroidal mode number of n=1 and n$$sim$$7, respectively, seem to be more important for the HRS H-mode plasmas. To investigate their interaction, bi-spectral analysis is applied for the magnetic probe data. It is found to be a powerful tool, exhibiting the phase-coupled oscillations between two types of edge MHD activities having n=1 and n$$sim$$7.

Journal Articles

Reduced divertor heat loads, plasma shape effects, and radial electric field structures in JFT-2M HRS H-mode plasmas

Kamiya, Kensaku; Kawashima, Hisato; Ido, Takeshi*; Oyama, Naoyuki; Bakhtiari, M.*; Kasai, Satoshi; Kusama, Yoshinori; Miura, Yukitoshi; Ogawa, Hiroaki; Tsuzuki, Kazuhiro; et al.

Nuclear Fusion, 46(2), p.272 - 276, 2006/02

 Times Cited Count:3 Percentile:11.12(Physics, Fluids & Plasmas)

An attractive operational regime without any large ELMs, namely High Recycling Steady (HRS) H-mode, was found on JFT-2M during Y2000 campaign after boronization. Recent experiments have concentrated on the studies of the access conditions for the HRS regime, in terms of the pedestal parameters. The HRS regime was more likely at higher edge density and lower edge temperature, which corresponds to the normalized electron collisionality of 1 in the plasma edge region.

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:39 Percentile:76.46(Physics, Fluids & Plasmas)

no abstracts in English

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:51 Percentile:83.25(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

Energy loss for grassy ELMs and effects of plasma rotation on the ELM characteristics in JT-60U

Oyama, Naoyuki; Sakamoto, Yoshiteru; Isayama, Akihiko; Takechi, Manabu; Gohil, P.*; Lao, L. L.*; Snyder, P. B.*; Fujita, Takaaki; Ide, Shunsuke; Kamada, Yutaka; et al.

Nuclear Fusion, 45(8), p.871 - 881, 2005/08

 Times Cited Count:116 Percentile:95.69(Physics, Fluids & Plasmas)

The grassy ELM is characterized by the high frequency periodic collapse up to $$sim$$kHz, which is $$sim$$15 times faster than that for type I ELM. A divertor peak heat flux due to grassy ELMs is less than 10% of that for type I ELMs. This smaller heat flux is caused by narrower radial extent of the collapse of temperature pedestal. The different radial extent between type I ELMs and grassy ELMs qualitatively agrees with the different radial distribution of the eigen function of the ideal MHD stability analysis. The ratio of ELM energy loss for grassy ELMs to the pedestal stored energy was 0.4-1%. In high triangularity regime, ELM amplitude, frequency and type can be changed from type I ELM to high frequency grassy ELM as counter plasma rotation was increased. In low triangularity regime, on the other hand, the complete ELM suppression (QH-mode) has been achieved, when the plasma position is optimized with CTR-NBIs. The existence of the edge fluctuations localized in pedestal region may reduce the pedestal pressure, and therefore the QH-mode can be sustained for long time up to 3.4s.

Journal Articles

Reduced heat transport between edge-localized-mode bursts at low collisionality and small poloidal larmor radius

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

Physical Review Letters, 95(3), p.035003_1 - 035003_4, 2005/07

 Times Cited Count:15 Percentile:63.21(Physics, Multidisciplinary)

Non-dimensional parameter dependence of heat transport between ELMs is examined for H mode plasmas. At lower edge collisionality, the heat flux assigned to the heat transport between ELMs is reduced and the ELM loss power is enhanced. During the inter-ELM phase, the energy confinement time becomes larger with decreasing the edge collisionality and poloidal Larmar radius. The electron heat diffusivity between ELMs is reduced to the level of ion neoclassical transport in the plasma edge region which is affected by ELM burst.

Journal Articles

Pedestal characteristics of H-mode plasmas in JT-60U and ASDEX Upgrade

Urano, Hajime; Kamada, Yutaka; Takizuka, Tomonori; Suttrop, W.*; Horton, L.*; Lang, P.*; Kubo, Hirotaka; Oyama, Naoyuki; Takenaga, Hidenobu; Asakura, Nobuyuki

Purazuma, Kaku Yugo Gakkai-Shi, 81(4), p.280 - 287, 2005/04

Role of the pedestal structure in ELMy H-mode plasmas for the core energy confinement and for the ELM energy losses have been investigated in JT-60U and ASDEX Upgrade. The confinement degradation seen at higher densities is attributed to the reduction of the pedestal temperature limited by the ELM activities and the stiffness of the temperature profiles. In high triangularity or impurity seeded H-modes, in which higher energy confinement is generally achieved, higher pedestal temperature is obtained by the improvement of the edge MHD stability or the density profile peaking, respectively. The upper bound of the ELM energy loss is characterised by the pedestal energy. The energy transport in between ELMs enhanced with increasing the pedestal collisionality reduces the ELM loss power fraction. It is also shown in ASDEX Upgrade that the continuous pellet injection is valid for the integrated performance of smaller ELM losses and favourable core confinement.

Journal Articles

Overview of goals and performance of ITER and strategy for plasma-wall interaction investigation

Shimada, Michiya; Costley, A. E.*; Federici, G.*; Ioki, Kimihiro*; Kukushkin, A. S.*; Mukhovatov, V.*; Polevoi, A. R.*; Sugihara, Masayoshi

Journal of Nuclear Materials, 337-339, p.808 - 815, 2005/03

 Times Cited Count:63 Percentile:96.36(Materials Science, Multidisciplinary)

ITER is an experimental fusion reactor for investigation and demonstration of burning plasmas, characterised of its heating dominated by alpha-particle heating. ITER is a major step from present devices and an indispensable step for fusion reactor development. ITER's success largely depends on the control of plasma-wall interactions(PWI), with power and particle fluxes and time scales one or two orders of magnitude larger than in present devices. The strategy for control of PWI includes the semi-closed divertor, strong fuelling and pumping, disruption and ELM control, replaceable plasma-facing materials and stepwise operation.

Journal Articles

Parallel and radial transport of ELM plasma in the SOL and divertor of JT-60U

Asakura, Nobuyuki; Takechi, Manabu; Oyama, Naoyuki; Nakano, Tomohide

Journal of Nuclear Materials, 337-339, p.712 - 716, 2005/03

 Times Cited Count:14 Percentile:68.69(Materials Science, Multidisciplinary)

Fast sampling diagnostics such as Langmuir probes and magnetic pick-up coils were developed in JT-60U. ELM radial expansion was important to understand the heat and particle load on the first wall. Enhancement and radial expansion of the SOL plasma just after ELM were investigated at Low-Field-Side and High-Field-Side. Ion saturation current ($$j$$$$_{s}$$) profile was described by two-exponential fit (i.e. 1st and 2nd lgi). Enhancement of the particle flux was different in poloidal location: particle flux profile became very flat, in particular, at HFS. Radial expansion speed at LFS was evaluated in the range of 1-3 km/s. ELM plasma flux in LFS and HFS divertors was investigated. Fast changes of js and floating potential (Vf) were measured. Large negative Vf was observed and durations of the negative js and Vf were $$sim$$100 ms, which was shorter than heat deposition ($$sim$$250 ms). The large negative js and Vf near both strike-points suggested fast electron deposition rather than thermal electric current. Influence of the divertor sheath on the heat deposition time is discussed.

Journal Articles

Multi-machine comparisons of H-mode separatrix densities and edge profile behaviour in the ITPA SOL and Divertor Physics Topical Group

Kallenbach, A.*; Asakura, Nobuyuki; Kirk, A.*; Korotkov, A.*; Mahdavi, M. A.*; Mossessian, D.*; Porter, G. D.*

Journal of Nuclear Materials, 337-339, p.381 - 385, 2005/03

 Times Cited Count:65 Percentile:96.65(Materials Science, Multidisciplinary)

Edge profile data for H-mode discharges in 6 tokamaks have been analysed with the main focus on the edge density profile as well as electron temperature and density gradient lengths and steep gradient zone widths. A uniform procedure of data treatment and assignment of the separatrix position via power balance allowed to put the multi-machine data on an even base. The machine size appears to be the leading parameter for the width of the steep edge transport barrier gradient zone, as well as for the temperature decay length at the separatrix. Effects associated with neutral penetration physics are visible in the edge density profile.

Journal Articles

Study of plasma wall interactions in the long-pulse NB-heated discharges of JT-60U towards steady-state operation

Takenaga, Hidenobu; Asakura, Nobuyuki; Higashijima, Satoru; Nakano, Tomohide; Kubo, Hirotaka; Konoshima, Shigeru; Oyama, Naoyuki; Isayama, Akihiko; Ide, Shunsuke; Fujita, Takaaki; et al.

Journal of Nuclear Materials, 337-339, p.802 - 807, 2005/03

 Times Cited Count:14 Percentile:68.69(Materials Science, Multidisciplinary)

no abstracts in English

143 (Records 1-20 displayed on this page)