Refine your search:     
Report No.
 - 
Search Results: Records 1-16 displayed on this page of 16
  • 1

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

Gyrofluid simulation on the nonlinear excitation and radial structure of geodesic acoustic modes in ITG turbulence

Li, J. Q.*; Kishimoto, Yasuaki; Miyato, Naoaki; Miki, Kazuhiro*; Anderson, J.*; Shi, B. R.*

Journal of Physics; Conference Series, 123, p.012027_1 - 012027_11, 2008/08

 Times Cited Count:1 Percentile:46.61

The nonlinear excitation and saturation mechanism of geodesic acoustic mode (GAM), as well as its radial structure, in tokamak plasmas are investigated by applying a newly well-benchmarked gyrofluid model. At first, an empirical closure relation for the conventional three-field gyrofluid modeling is presented for ion temperature gradient (ITG) fluctuations and the GAMs. The zonal flow (ZF) damping is precisely examined by comparing with theoretical predictions and other kinetic calculations. Then, a local code and the global version are advanced to simulate the nonlinear excitation of the GAMs by ITG fluctuations. It is found that the GAM instability can be nonlinearly excited under the competition between the nonlinear driving and the collisionless damping. The pump amplitude threshold of the GAM instability is higher than that of the ZF instability. Meanwhile, the unstable GAMs are mainly saturated by the intrinsic Landau damping. Furthermore, the radial structure of the GAMs is shown as $$k_rrho_ileq 1.0$$.

Journal Articles

Progress and issues in understanding the physics of ELM dynamics, ELM mitigation, and ELM control

Oyama, Naoyuki

Journal of Physics; Conference Series, 123, p.012002_1 - 012002_17, 2008/00

 Times Cited Count:37 Percentile:99.35

This paper reports progress and issues in physics understanding of dynamics, mitigation and control of ELMs, which have been recognized as one of the important issues in ITER. As for the ELM dynamics, studies of ELM precursor, filamentary structures during the collapse phase, dependence of ELM energy loss on the toroidal rotation and edge stability are progressed. In the small/no ELM regimes, expansion of the operational space toward low collisionality region has been achieved in type V ELM. In grassy ELM regime and QH-mode regime, ELM frequency dependence and EHO characteristics in term of edge rotation have been observed, respectively. As for the ELM control, the applicability of pellet pacing and external ELM control coils to ITER is discussed. Since the effect of toroidal rotation is now recognized as a fundamental parameter, the reliable prediction of edge rotation in ITER becomes more important.

Journal Articles

Effect of toroidal field ripple and toroidal rotation on H-mode performance and ELM characteristics in JET/JT-60U similarity experiments

Oyama, Naoyuki; Saibene, G.*; Kamada, Yutaka; Kamiya, Kensaku; Loarte, A.*; L$"o$nnroth, J.*; Parail, V.*; Sakamoto, Yoshiteru; Salmi, A.*; Sartori, R.*; et al.

Journal of Physics; Conference Series, 123, p.012015_1 - 012015_13, 2008/00

 Times Cited Count:8 Percentile:91.13

The effect of the toroidal field ripple and the edge toroidal rotation on H-mode and pedestal performance as well as ELM characteristics are investigated both in JET and JT-60U. In JT-60U, the amplitude of TF ripple was reduced from 1.2 % to 0.5 % after the installation of ferritic steel tiles. In JET, the ripple amplitude can actively be varied. In both devices, edge rotation in the same direction to the plasma current was reduced with increasing the ripple amplitude. Even at the same amplitude of 0.5 %, the achievable edge rotation in JT-60U was still lower than that in JET. A series of power and density scans performed at several ripple amplitude indicated that plasmas with smaller ripple amplitude and/or larger co-rotation are favorable to achieve higher pedestal pressure and plasma confinement in both devices. As for ELM characteristics, larger co-rotation seems to increase the ELM energy loss together with the reduction of the ELM frequency.

Journal Articles

Effect of equilibrium properties on the structure of the edge MHD modes in tokamaks

Aiba, Nobuyuki; Hayashi, Nobuhiko; Takizuka, Tomonori; Tokuda, Shinji; Ozeki, Takahisa

Journal of Physics; Conference Series, 123, p.012008_1 - 012008_11, 2008/00

 Times Cited Count:3 Percentile:74.64

We investigate numerically the effects of the equilibrium properties on the structure of the edge MHD modes in tokamaks. In particular, we focus on the effects of the plasma shape and the pressure profile inside the top of the pedestal. As the results of numerical analyses, we find that the structure of the unstable MHD mode expands to the plasma core region even when the width of the edge pedestal region, and the mode structure can expand deeply in strongly-shaped plasmas. This deeply expansion in strongly-shaped plasma is because the difference of the stabilizing effect of the ideal ballooning mode between the plasma edge region (including the edge pedestal region) and the region inside the pedestal in strongly shaped plasma is larger than that in weakly shaped plasma. This difference allows to destabilize the MHD mode whose structure extend from the edge pedestal region to the region inside the pedestal in strongly shaped plasma.

Journal Articles

Simulation study of density dynamics effect on the ELM behavior with TOPICS-IB

Hayashi, Nobuhiko; Takizuka, Tomonori; Aiba, Nobuyuki; Ozeki, Takahisa; Oyama, Naoyuki

Journal of Physics; Conference Series, 123, p.012025_1 - 012025_10, 2008/00

 Times Cited Count:5 Percentile:84.58

Density dynamics effect on ELM has been studied by TOPICS-IB. The ELM particle loss is found to almost independent on the collisionality, as shown in experiments, due to the density profile before ELM and the increase of the SOL density during ELM. It is confirmed by varying the density and the temperature instead of artificially enhancing the collisionality that the collisionality dependence of the ELM energy loss is caused by the bootstrap current and the SOL transport. Additionally, ion convective and charge-exchange losses are found to enhance the collisionality dependence due to the equipartition effect.

Journal Articles

ELM propagation in the low- and high-field-side Scrape-off Layer of the JT-60U tokamak

Asakura, Nobuyuki; Kawashima, Hisato; Ono, Noriyasu*; Matsunaga, Go; Nakano, Tomohide; Oyama, Naoyuki

Journal of Physics; Conference Series, 123, p.012009_1 - 012009_11, 2008/00

 Times Cited Count:3 Percentile:74.64

In JT-60U, the filament structure was measured at three poloidal locations, and its time evolution were investigated at the inner (high-field-side) SOL as well as outer (low-field-side) SOL. At the inner SOL, filament structure with 7-8 multi-peaks was, for the first time, determined only close to sepatratrix. Delay of the first peak after start of MHD activity was faster than characteristic time of the parallel convection from the outer midplane, and Mach numbers reached ion sonic level. These results show that ELM filaments extend from outer to inner plasma edge, and a part of the filaments are exhausted to the inner SOL. Toroidal mode number (n) and size of the filament (dz) were evaluated from the interval of the multi-peaks and duration of each peak: n 15-25 and dz 2-4 cm at the HFS SOL, and n was smaller than and dz was comparable to those at the LFS SOL. After the multi-peak appearance, flow reversal of SOL plasma was generated over wide region of the inner SOL.

Journal Articles

Comparison of the spatial and temporal structure of type-I ELMs

Kirk, A.*; Asakura, Nobuyuki; Boedo, J. A.*; Beurskens, M.*; Counsell, G. F.*; Eich, T.*; Fundamenski, W.*; Herrmann, A.*; Kamada, Yutaka; Leonard, A. W.*; et al.

Journal of Physics; Conference Series, 123, p.012011_1 - 012011_10, 2008/00

 Times Cited Count:22 Percentile:97.86

A comparison of the spatial and temporal evolution of the filamentary structures observed during type I ELMs is presented from a variety of diagnostics and machines. There is evidence that these filaments can be detected inside the LCFS prior to ELMs. The filaments do not have a circular cross section instead they are elongated in the perpendicular (poloidal) direction and this size appears to increase linearly with the minor radius of the machine. The filaments start rotating toroidally/poloidally with velocities close to that of the pedestal. This velocity then decreases as the filaments propagate radially. It is most likely that the filaments have at least their initial radial velocity when they are far out into the SOL. The dominant loss mechanism is through parallel transport and the transport to the wall is through the radial propagation of these filaments. Measurements of the filament energy content show that each filament contains up to 2.5 % of the energy released by the ELM.

Journal Articles

Effects of low central fuelling on density and ion temperature profiles in reversed shear plasmas on JT-60U

Takenaga, Hidenobu; Ide, Shunsuke; Sakamoto, Yoshiteru; Fujita, Takaaki; JT-60 Team

Journal of Physics; Conference Series, 123, p.012037_1 - 012037_8, 2008/00

 Times Cited Count:2 Percentile:64.11

Effects of low central fuelling on density and ion temperature profiles have been investigated using negative ion based neutral beam injection and electron cyclotron heating (ECH) in reversed shear plasmas on JT-60U. Strong internal transport barrier (ITB) was maintained in density and ion temperature profiles, when central fuelling was decreased by switching positive ion based neutral beam injection to ECH after the strong ITB formation. Similar density and ion temperature ITBs were formed both with low and high central fuelling during the plasma current ramp-up phase. Strong correlation between the density gradient and the ion temperature gradient was observed, indicating that particle transport and ion thermal transport are strongly coupled or the density gradient assists the ion temperature ITB formation through suppression of ion temperature gradient mode. These results support that the density and ion temperature ITBs can be formed under reactor relevant conditions.

Journal Articles

Three-dimensional neutral transport simulation in the JT-60U H-mode plasmas

Nakashima, Yosuke*; Higashizono, Yuta*; Kawano, Hirokazu*; Takenaga, Hidenobu; Asakura, Nobuyuki; Oyama, Naoyuki; Kamada, Yutaka; Yatsu, Kiyoshi*

Journal of Physics; Conference Series, 123, p.012029_1 - 012029_7, 2008/00

 Times Cited Count:4 Percentile:80.6

The first results of a fully three-dimensional (3-D) Monte-Carlo simulation using DEGAS ver.63 code applied to the JT-60U tokamak and analysis of neutral behavior in H-mode plasmas are described. A precise mesh structure including isolated dome, baffle and divertor plates is built-up and the simulation space is extended from SOL/divertor to core plasma region. Benchmarking with 2-dimensional simulation with the DEGAS2 code successfully showed the validity of the present simulation. Result of 3-D simulation in the JT-60U plasma with gas puffing indicates the significant localization of neutrals around the gas puffer and the detail of neutral diffusion in toroidal and poloidal directions are clarified. The dependence of plasma density on the neutral penetration and ionization area are also discussed in different H-mode discharges.

Journal Articles

A Model of GAM intermittency near critical gradient in toroidal plasmas

Miki, Kazuhiro*; Kishimoto, Yasuaki; Miyato, Naoaki; Li, J. Q.*

Journal of Physics; Conference Series, 123, p.012028_1 - 012028_14, 2008/00

 Times Cited Count:4 Percentile:80.6

We have constructed a four-field minimum model that describes the growing intermittency of turbulence associated with the geodesic acoustic mode (GAM) observed in our toroidal Landau-fluid simulations. The intermittent dynamics are well reproduced by the model for the reference parameters used in the simulation. The model can also reproduce more nature of turbulent transport associated with the GAM, such as a single burst leading to a full quench of turbulence and also a steady state turbulence mixed with steady state zonal flows and GAMs. Investigating the behaviour of the solution trajectories around the fixed points in four-dimensional phase space, we examine the comprehensive properties of the model and identify the bifurcation property between Dimits shift and steady state turbulence regimes, which correspond to different eigen-states.

Journal Articles

Power requirement for accessing the H-mode in ITER

Martin, Y. R.*; Takizuka, Tomonori; ITPA CDBM H-mode Threshold Database Working Group*

Journal of Physics; Conference Series, 123, p.012033_1 - 012033_11, 2008/00

 Times Cited Count:317 Percentile:100

no abstracts in English

Journal Articles

Preface; 11th IAEA Technical Meeting on H-mode Physics and Transport Barriers

Takizuka, Tomonori

Journal of Physics; Conference Series, 123, P. 011001_1, 2008/00

no abstracts in English

Oral presentation

Two-dimensional full particle simulation of the formation of electrostatic field in a tokamak plasma

Takizuka, Tomonori; Hosokawa, Masanari*

no journal, , 

no abstracts in English

Oral presentation

Electromagnetic effects on zonal mode generation and turbulent transport in tokamak plasmas

Miyato, Naoaki; Kishimoto, Yasuaki; Li, J.*; Tokuda, Shinji

no journal, , 

Electromagnetic or finite beta effects on generation of zonal modes, which include zonal magnetic fields as well as the zonal flows, and turbulent transport are investigated by global fluid simulations of electromagnetic ion temperature gradient (ITG) driven turbulence. The zonal magnetic fields are generated at low order rational surface. Coarse choice of toroidal modes affects zonal magnetic field generation. Three drives for the zonal flows, Reynolds stress, Maxwell stress and geodesic transfer, are analysed. The Reynolds stress contribution balances with the geodesic transfer and drives the zonal flows in almost whole region. It is found that the Reynolds stress and the geodesic transfer contributions change sign at low order rational surfaces. This is not observed in the electrostatic case.

Oral presentation

Enhanced H-mode energy confinement with co-toroidal rotation in JT-60U

Urano, Hajime; Takenaga, Hidenobu; Fujita, Takaaki; Kamada, Yutaka; Koide, Yoshihiko; Oyama, Naoyuki; Yoshida, Maiko

no journal, , 

To understand the improved energy confinement with co-toroidal rotation, relation between heat transport in the plasma core and toroidal rotation was examined. Heat transport in the plasma core varies while sustaining self-similar temperature profile in the variations of toroidal rotation profiles. Pedestal pressure became larger with toroidal rotation in co-direction. H-mode confinement enhanced with co-toroidal rotation is determined by increased pedestal and reduced transport brought on by profile resilience. Local effect of toroidal rotation profile in the plasma core on heat transport is very weak.

Oral presentation

MHD stability due to internal transport barrier and its effect on the transport

Ozeki, Takahisa; Aiba, Nobuyuki; Hayashi, Nobuhiko; Takizuka, Tomonori; Tokuda, Shinji

no journal, , 

The advanced tokamak plasma has strongly coupling of physical-factors with widely different time, which make the complexity and autonomy. Therefore, it is a crucial issue to clarify these complex plasmas and to control the autonomous plasma. Modeling of each physical factor and an integration of models are useful to understand the complex plasma and to control the autonomous plasma. JAEA has developted the intergated simulation code TOPICS-IB with the stability code MARG2D. Here, we investigate an effect of the local steep pressure gradient at the internal transport barrier on the MHD stability. Also, the dynamic behaviours after the collapse by the MHD instability are simulated, and the sustainment of the advanced tokamak plasma is discussed.

16 (Records 1-16 displayed on this page)
  • 1