Refine your search:     
Report No.
 - 
Search Results: Records 1-13 displayed on this page of 13
  • 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

Fusion; The Energy of the Universe

McCracken, G.*; Stott, P.*; Iiyoshi, Atsuo*; Muraoka, Katsunori*; Nakai, Sadao*; Shimada, Michiya

Kaku Yugo; Uchu No Enerugi O Watashitachi No Te Ni, 326 Pages, 2015/00

Fusion; The Energy of the Universe, 2e is an essential reference providing basic principles of fusion energy from its history to the issues and realities progressing from the present day energy crisis. The book provides detailed developments and applications for researchers entering the field of fusion energy research. This second edition includes the latest results from the National Ignition Facility at the Lawrence Radiation Laboratory at Livermore, CA, and the progress on the International Thermonuclear Experimental Reactor (ITER) tokamak programme at Caderache, France.

Journal Articles

Particle transport of LHD

Tanaka, Kenji*; Kawahata, Kazuo*; Tokuzawa, Tokihiko*; Akiyama, Tsuyoshi*; Yokoyama, Masayuki*; Shoji, Mamoru*; Michael, C. A.*; Vyacheslavov, L. N.*; Murakami, Sadayoshi*; Wakasa, Arimitsu*; et al.

Fusion Science and Technology, 58(1), p.70 - 90, 2010/07

 Times Cited Count:20 Percentile:81.23(Nuclear Science & Technology)

Particle confinement processes were studied in detail on LHD. Diffusion coefficients (D) and convection velocities (V) were estimated from density modulation experiments. The magnetic configuration and collisionality were widely scanned in order to investigate parameter dependences of D and V. In order to study the effect of the magnetic configuration, magnetic axis positions (R$$_{ax}$$) were scanned from 3.5 m to 3.9 m. This scan changed the magnetic ripples quite significantly, enabling the effects of neoclassical properties on measured values to be widely elucidated. Dependences of electron temperature (T$$_{e}$$) and helically trapped normalized collsionality ($$nu$$$$_{h}^{*}$$), where $$nu$$$$_{h}^{*}$$=1 indicates a rough boundary between the 1/$$nu$$ and plateau regimes, were examined using the heating power scan of neutral beam injection (NBI). It was found out that generally larger (or smaller) contributions of neoclassical transport resulted in more hollow (or peaked) density profiles. The larger neoclassical contribution was found to be situated at a more outwardly shifted R$$_{ax}$$ for the same T$$_{e}$$, and higher T$$_{e}$$ or lower $$nu$$$$_{h}^{*}$$ at each R$$_{ax}$$. However, it is to be noted that R$$_{ax}$$=3.5 m showed different characteristics from these trends in that this case showed a more peaked density profile at higher T$$_{e}$$.

Journal Articles

Experimental investigation of particle pinch associated with turbulence in LHD heliotron and JT-60U tokamak plasmas

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Michael, C.*; Vyacheslavov, L. N.*; Yokoyama, Masayuki*; Yamada, Hiroshi*; Oyama, Naoyuki; Urano, Hajime; Kamada, Yutaka; et al.

Proceedings of 22nd IAEA Fusion Energy Conference (FEC 2008) (CD-ROM), 8 Pages, 2008/10

Comparative studies were carried out in LHD heliotron and JT-60U tokamak plasmas to elucidate the most essential parameter(s) for control of density profiles in toroidal systems. A difference in the collisionality dependence was found between the two devices. In LHD, the density peaking factor decreased with decrease of the collisionality at the magnetic axis position (R$$_{rm au}$$) 3.6 m, while the density peaking factor gradually increased with a decreased of collisionality at R$$_{rm au}$$ = 3.5 m. On the other hand, in JT-60U, the density peaking factor clearly increased with a decrease of the collisionality. The difference in the collisionality dependence between R$$_{rm au}$$ = 3.5 and R$$_{rm au}$$ = 3.6 m is likely due to the contribution of the anomalous transport. At R$$_{rm au}$$ = 3.5 m, larger anomalous transport caused a similar collisionality dependence. Change of the fluctuation property was observed with different density profiles in the plasma core region on both devices. In JT-60U, the increase of the radial coherence was observed with higher density peaking profile suggesting enhanced diffusion and inward directed pinch. For a magnetic axis positions (R$$_{rm au}$$) at 3.6 m in LHD, the increase of the fluctuation power with an increase in P$$_{rm NB}$$ was observed for a hollow density profile suggesting an increase on diffusion due to anomalous processes. Change of density profiles from peaked to hollow indicates change in the convection direction. This is due to increase in neoclassical processes. The reduction of the density peaking factor with increase of P$$_{rm NB}$$ in LHD is partly due to the neoclassical effect and partly due to the anomalous effect.

Journal Articles

Particle transport and fluctuation characteristics around the neoclassically optimized configurations in LHD

Tanaka, Kenji*; Michael, C.*; Vyacheslavov, L. N.*; Yokoyama, Masayuki*; Murakami, Sadayoshi*; Wakasa, Arimitsu*; Takenaga, Hidenobu; Muraoka, Katsunori*; Kawahata, Kazuo*; Tokuzawa, Tokihiko*; et al.

Plasma and Fusion Research (Internet), 3, p.S1069_1 - S1069_7, 2008/08

Density profiles in LHD were measured and particle transport coefficients were estimated from density modulation experiments in LHD. The dataset of different magnetic axis, toroidal magnetic filed and heating power provided data set of widely scanned neoclassical transport. At minimized neoclassical transport configuration ($$R$$$$_{rm ax}$$ = 3.5 m, $$B$$$$_{rm t}$$ = 2.8 T) showed peaked density profile. Its peaking factor increased gradually with decrease of collisional frequency. This is a similar result observed in JT-60U. At other configuration, peaking factor reduced with decrease of collsional frequency. Data set showed that larger contribution of neoclassical transport produced hollowed density profile. Comparison between neoclassical and estimated particle diffusivity showed different minimum condition. Clear difference of spatial profile of turbulence was observed between hollowed and peaked density profiles. Major part of fluctuation existed in the unstable region of ion temperature gradient mode.

Journal Articles

Comparisons of density profiles in JT-60U tokamak and LHD helical plasmas with low collisionality

Takenaga, Hidenobu; Tanaka, Kenji*; Muraoka, Katsunori*; Urano, Hajime; Oyama, Naoyuki; Kamada, Yutaka; Yokoyama, Masayuki*; Yamada, Hiroshi*; Tokuzawa, Tokihiko*; Yamada, Ichihiro*

Nuclear Fusion, 48(7), p.075004_1 - 075004_11, 2008/07

 Times Cited Count:29 Percentile:74.68(Physics, Fluids & Plasmas)

In order to understand particle transport systematically in toroidal plasmas, electron density profiles were compared in JT-60U tokamak and LHD helical plasmas with low collisionality. Peakedness of density profiles increased with decreasing collisionality in ELMy H-mode plasmas of JT-60U, when the collisionality at half the minor radius was in the collisionless regime. Collisionality dependence of density profiles in LHD plasmas was similar to that in JT-60U plasmas in the same collisionality regime, when neoclassical transport was suppressed by geometrical optimization. On the other hand, in the LHD plasmas having relatively larger neoclassical transport than that in the above case, peakedness of density profiles decreased with decreasing collisionality. Neoclassical transport enhanced by the non-axisymmetric effect significantly affected density profiles with low collisionality in LHD plasmas. Density profiles in LHD plasmas tended to approach those in JT-60U, which are dominated by anomalous transport, as the contribution of neoclassical transport was reduced.

Journal Articles

A Model for striation formation in ac PDP discharges

Muraoka, Katsunori*; Azumi, Masafumi; Suzuki, Keizo*; Yamagata, Yukihiko*; Yagi, Masatoshi*

Journal of Physics D; Applied Physics, 39(10), p.2135 - 2139, 2006/05

 Times Cited Count:6 Percentile:25.4(Physics, Applied)

A model is presented to explain the mechanism of striation formation in ac plasma display panel discharges. A simple Monte Carlo simulation code follows the electron motions in such discharges and features of striations obtained by the simulation are consistent with experimental results. The model suggests the indirect measurement of electric field in a micro-discharges from the space pich of striations.

Journal Articles

Results of ITER physics R&D, 7; Plasma Diagnostics

Zushi, Hideki*; Sugie, Tatsuo; Kusama, Yoshinori; Sasao, Mamiko*; Mitarai, Osamu*; Nishitani, Takeo; Nagashima, Akira; Muraoka, Katsunori*

Purazuma, Kaku Yugo Gakkai-Shi, 76(2), p.145 - 162, 2000/02

no abstracts in English

Oral presentation

Particle transport in LHD and comparisons with tokamaks

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Urano, Hajime; Michael, C.*; Vyacheslavov, L. N.*; Yokoyama, Masayuki*; Yamagishi, Osamu*; Murakami, Sadayoshi*; Wakasa, Arimitsu*; et al.

no journal, , 

In order to understand particle transport systematically in toroidal plasmas, a density profile was compared in LHD helical and JT-60U tokamak plasmas. In large tokamak devices such as JT-60U, the density profile is always peaked and the peaked density profile can be explained based on outward diffusion flux and inward convection flux driven by microinstability. A peaking factor of the density profile was increased with decreasing collisionality. On the other hand, the density profile was changed from peaked one to hollow one depending on discharge conditions in LHD. The hollow density profile can be explained based on outward convection flux driven by neoclassical transport and inward diffusion flux driven by microinstability. In the configuration with a small helical ripple, where the neoclassical transport is reduced, the density profile tended to be peaked and dependence of the peaking factor on the collisionality was similar to that in tokamak plasmas. These results indicated that magnetic field ripple and microinstability are some of the main mechanisms determining the density profile.

Oral presentation

Electron density profile and turbulence in toroidal plasmas

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Michael, C.*; Vyacheslavov, L. N.*; Yokoyama, Masayuki*; Yamada, Hiroshi*; Murakami, Sadayoshi*; Wakasa, Arimitsu*; Kawahata, Kazuo*; et al.

no journal, , 

In order to understand mechanisms for determining density profiles in toroidal plasmas, density profiles were compared in JT-60U tokamak and LHD helical plasmas. Transport theory indicates that neoclassical transport is enhanced in helical plasmas with low collisionality due to helical ripple. In JT-60U plasmas, density peaking increased with decreasing the collisionality. In LHD plasmas for magnetic axis (Rax) of 3.5m with small effective helical ripple, density peaking slightly increased with decreasing the collisionality as similar to that in tokamak plasmas. On the other hand, in LHD plasmas for Rax$$>$$3.6m with relatively large effective helical ripple, density profile became hollow as the collisionality decreased. Different turbulence structures are observed for Rax=3.5m and Rax=3.6m in LHD plasmas. Turbulence propagated towards electron diamagnetic direction for Rax=3.5m and towards ion diamagnetic direction for Rax=3.6m. This difference could be related to the difference of density profiles, as well as difference of neoclassical transport. Furthermore, when density decreased in the core region due to increase of electron temperature, it was found that turbulence was first modified in the edge region and then in the core region.

Oral presentation

Response of turbulence under change of density profiles in toroidal devices

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Michael, C.*; Vyacheslavov, L. N.*; Mishchenko, A.*; Yokoyama, Masayuki*; Yamada, Hiroshi*; Oyama, Naoyuki; Urano, Hajime; et al.

no journal, , 

Comparative studies were carried out in LHD heliotron and JT-60U tokamak plasmas to elucidate effects of turbulence transport on density profiles in toroidal systems. A difference in the collisionality dependence was found between the two devices. In LHD, the density peaking factor decreased with decrease of the collisionality at the magnetic axis position (R$$_{ax}$$) of 3.6 m. On the other hand, in JT-60U, the density peaking factor clearly increased with a decrease of the collisionality. For R$$_{ax}$$=3.6 m in LHD, the increase of the fluctuation power with an increase in P$$_{NB}$$ was observed for a hollow density profile suggesting an increase on diffusion due to anomalous processes. In JT-60U, the increase of the radial coherence was observed with higher density peaking profile suggesting enhanced diffusion and inward directed pinch. The effects of curvature pinch on density profiles were also investigated in both devices. The curvature pinch produces a peaked density profile in JT-60U and a hollow density profile in LHD depending on their magnetic shear. However, these effects were too small to explain the density profiles observed in both devices.

Oral presentation

Density profiles and turbulence in tokamak and helical plasmas

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Michael, C.*; Vyacheslavov, L. N.*

no journal, , 

In order to understand transport properties in toroidal plasmas, density profiles were compared in tokamak and helical plasmas. The density profiles tended to be peaked as the contribution of anomalous transport increases in JT-60U and LHD plasmas. In JT-60U ELMy H-mode plasmas and LHD plasmas at magnetic axis Rax=3.5 m, where the contribution of anomalous transport is large, a peaking factor of the density profile increased with decreasing normalized collisionality $$nu_{b}$$*. In LHD plasmas at Rax=3.6 m, where the contribution of anomalous transport is small, this factor decreased with decreasing $$nu_{b}$$* and the density profile became hollow one. In JT-60U ELMy H-mode plasmas, coherence increased as the density profile becomes peaked one. On the other hand, when the peaking factor of the density profile decreased with increasing heating power in LHD plasmas at Rax=3.6 m, anomalous diffusion increased due to increase in turbulence level and the direction of the convection velocity changed from inward to outward due to neoclassical transport.

Oral presentation

Response of turbulence associated with the change of density profiles in LHD heliotron and JT-60U tokamak

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Yoshida, Maiko; Michael, C.*; Vyacheslavov, L. N.*; Mikkelsen, D. R.*; Yokoyama, Masayuki*; Oyama, Naoyuki; Urano, Hajime; et al.

no journal, , 

Density profile and turbulence was compared in JT-60U tokamak and LHD heliotron. Density peaking increases with decrease of collisionality in JT-60U. Density gradient predicted from zero flux condition agrees within factor 2 for Te/Ti=1, but large discrepancies are found for Te/Ti $$<$$ =0.5. In LHD, peaked profile and increase of density peaking with decrease of collisionality are found in strong magnetic hill configuration (Rax = 3.5 m). Hollowed-peaked density profile and increase of density peaking with increase of collisionality are found in weak magnetic hill configuration (Rax = 3.6 m). Fluctuation is localized in core gradient region and edge gradient region. Density gradient predicted from zero flux condition are compared. Then both cases agrees the sign and absolute values within factor 2.

Oral presentation

Comparison study of turbulence driven particle transport study by gyrokinetic linear/quasi linear simulation in JT-60U and LHD

Tanaka, Kenji*; Takenaga, Hidenobu; Muraoka, Katsunori*; Oyama, Naoyuki; Yoshida, Maiko; Mikkelsen, D. R.*; Michael, C. A.*; Vyacheslavov, L. N.*

no journal, , 

Density profile and turbulence was compared in JT-60U tokamak and LHD heliotron. Density peaking increases with decrease of collisionality in JT-60U. Density gradient predicted from zero flux condition agrees within factor 2 for Te/Ti=1, but large discrepancies are found for Te/Ti $$<$$ = 0.5. In LHD, peaked profile and increase of density peaking with decrease of collisionality are found in strong magnetic hill configuration (Rax = 3.5 m). Hollowed-peaked density profile and increase of density peaking with increase of collisionality are found in weak magnetic hill configuration (Rax = 3.6 m). Fluctuation is localized in core gradient region and edge gradient region. Density gradient predicted from zero flux condition are compared. Then both cases agrees the sign and absolute values within factor 2.

13 (Records 1-13 displayed on this page)
  • 1