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ABSTRACT: In order to measure the poloidal rotation velocity, a Doppler reflectometer has been developed in Large Helical Device (LHD). A remotely controlled antenna tilting system has been installed in an LHD vacuum vessel. A synthesizer is used as the source, and the operation microwave frequency ranges are ka-band and V-band. In LHD last experimental campaign we obtained the Doppler shifted signal, which was consistent with CXRS measurements.
The Review of scientific instruments 10/2012; 83(10):10E322. · 1.52 Impact Factor
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C Suzuki,
C S Harte,
D Kilbane,
T Kato,
H A Sakaue,
I Murakami,
D Kato,
K Sato,
N Tamura,
S Sudo,
M Goto,
R D'Arcy,
E Sokell,
G O'Sullivan
[show abstract]
[hide abstract]
ABSTRACT: We have measured extreme ultraviolet spectra from tungsten ions in the 20 nm region in plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The spectra following injection of a tungsten pellet into a hydrogen plasma were monitored by a grazing incidence spectrometer. A quasicontinuum spectral feature arising from an unresolved transition array (UTA) was observed around 20 nm in plasmas with temperatures below 1.0 keV. This structure is reasonably considered to be the same as observed in another tokamak device or laser-produced plasmas under low-temperature conditions. Atomic structure calculations have been performed for tungsten ions with open 5p, 5s and 4f subshells (W7 +–W27 +) to interpret the observed feature around 20 nm. Wavelengths and strengths for these transitions were calculated, and mean wavelengths and extent of the UTAs were compared with the observations, which suggests that the emission largely arises from n = 5–5 transitions in stages lower than W27 +.
Journal of Physics B Atomic Molecular and Optical Physics 08/2011; 44(17):175004. · 1.88 Impact Factor
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K. Nagaoka,
K. Ida,
M. Yoshinuma,
Y. Takeiri,
M. Yokoyama,
S. Morita,
K. Tanaka,
T. Ido,
A. Shimizu,
N. Tamura, [......],
H. Takahashi, C. Suzuki,
Y. Suzuki,
K. Ikeda,
M. Osakabe,
K. Tsumori,
H. Nakano,
O. Kaneko,
H. Yamada,
LHD Experiment Group
[show abstract]
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ABSTRACT: The peaked ion-temperature profile with steep gradient, the so-called ion internal transport barrier (ion ITB), was formed in the neutral beam heated plasmas on the Large Helical Device and the high-ion-temperature regime of helical plasmas has been significantly extended. The ion thermal diffusivity in the ion ITB plasma decreases down to the neoclassical transport level. The heavy ion beam probe observed the smooth potential profile with negative radial electric field (ion root) in the core region where the ion thermal diffusivity decreases significantly. The large toroidal rotation was also observed in the ion ITB core and the transport of toroidal momentum was analysed qualitatively. The decrease in momentum diffusivity with ion temperature increase was observed in the ion ITB core. The toroidal rotation driven by ion-temperature gradient, the so-called intrinsic rotation, is also identified.
Nuclear Fusion 07/2011; 51(8):083022. · 4.09 Impact Factor
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F. Watanabe,
K. Toi,
S. Ohdachi,
S. Sakakibara,
S. Morita,
H. Funaba,
T. Minami,
K. Narihara,
Y. Narushima, C. Suzuki,
K. Tanaka,
T. Tokuzawa,
K.Y. Watanabe,
I. Yamada,
LHD Experiment Group
[show abstract]
[hide abstract]
ABSTRACT: In the Large Helical Device (LHD), nonlinear evolution of strongly destabilized edge MHD modes, which are thought to be resistive interchange modes, induce repetitive bursts of magnetic fluctuations, soft X-ray (SX) fluctuations, and extreme ultra-violet (XUV) fluctuations, and generates a train of sharp spikes in H emission signals. These H spikes exhibit the character of edge localized mode (ELM). The ELM activities are also observed in high beta or high density L-mode plasmas having steep pressure gradient at plasma edge as well as H-mode plasmas with the L-H transition. The responsible instabilities for ELMs in LHD plasmas are thought to be resistive interchange modes, and are clearly different from those in a tokamak where peeling-ballooning modes are the candidates. The repetition frequency of ELMs (fELM) increases with the increase of external heating power, of which the character is similar to that of type I ELMs in tokamaks. The product of fELM and the relative ELM amplitude (δH/H) is roughly in proportion to the input heating power, where the ELM induced loss energy (ΔWp) increases with δH/H (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Beiträge aus der Plasmaphysik 07/2010; 50(6‐7):651 - 655.
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ABSTRACT: Magnetic axis shift (Shafranov shift) in a high density operational regime with an internal diffusion barrier (IDB) formation in Large Helical Device experiments has been studied using a two-dimensional imaging system composed of a soft x-ray CCD camera and beryllium filters. Magnetic axis positions are derived from the fitting of pre-calculated equilibria to measured (line-integrated) soft x-ray profiles assuming that the emissivity profile could be expressed by Fourier–Bessel series expansion. It has been clearly observed that the Shafranov shift in a plasma with IDB is much larger than that without IDB at a similar average beta value measured by a diamagnetic loop because of the strongly peaked pressure profile in this regime. According to systematic analyses of the Shafranov shift for various high density plasmas in this regime, the dependence of the Shafranov shift on the central beta value is summarized and compared with that in discharges without IDB.
Nuclear Fusion 05/2010; 50(6):064013. · 4.09 Impact Factor
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M. Yoshinuma,
K. Ida,
M. Yokoyama,
M. Osakabe,
K. Nagaoka,
S. Morita,
M. Goto,
N. Tamura, C. Suzuki,
S. Yoshimura,
H. Funaba,
Y. Takeiri,
K. Ikeda,
K. Tsumori,
O. Kaneko,
the LHD Experimental Group
[show abstract]
[hide abstract]
ABSTRACT: An extremely hollow profile of carbon impurity (denoted as an 'impurity hole') is observed associated with an increase in the ion temperature gradient after an impurity injection in the Large Helical Device. The central carbon density drops to 0.3% of the plasma density due to a strong outward convection driven by the ion temperature gradient, while an inward convection is predicted by neoclassical theory. Transport analysis gives a low diffusion coefficient of 0.4 m2 s−1 and an outward convection velocity of 3 m s−1 at half of the minor radius.
Nuclear Fusion 05/2009; 49(6):062002. · 4.09 Impact Factor
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ABSTRACT: We examined the effects of transforming growth factor-α (TGF-α) to develop a defined medium for in vitro maturation (IVM) of porcine (Sus scrofa domesticus) oocytes. Cumulus-oocyte complexes (COCs) were matured in porcine oocyte medium containing 3mg/mL polyvinyl alcohol (POM) and TGF-α (0, 1, 10, or 100 ng/mL) in the presence or absence of the gonadotropins equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). In the absence of gonadotropins, adding 10 ng/mL TGF-α increased (P
Theriogenology 01/2009; 72(6):841-850. · 1.96 Impact Factor
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ABSTRACT: Energy resolved soft x-ray imaging system using a charge coupled device camera and a multifilter disk has recently been installed to the Large Helical Device for the measurements in the long pulse discharges. Eight images with different cutoff energies are measured sequentially during a single discharge by rotating a filter disk mounting eight beryllium filters with different thicknesses. A tangential line-integrated profile for a specific photon energy range can be obtained by taking intensity difference between two images measured with a filter pair of adjacent thicknesses. The typical photon energy corresponding to each difference ranges from 1.9 to 4.8 keV with the bandwidth of 2–3 keV . In the initial results, the difference in the line-integrated soft x-ray profile by the energy range has been clearly observed. This diagnostic method can possibly be applied to the observation of the dependence of two dimensional soft x-ray profile on photon energy range especially if local non-Maxwellian component appears in electron energy distribution function.
Review of Scientific Instruments 11/2008; · 1.37 Impact Factor
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ABSTRACT: The formation of an edge transport barrier (ETB) has been observed in the high-density region (ne ~ 1.0 × 1020 m-3) of the Compact Helical System (CHS). The high-density ETB is observed in so-called 'reheat mode' discharge, an improved confinement mode in which the temperature increases due to the change of density profile by controlling gas-puff fueling. In the present study, we investigated the behaviour of the density profile and the density fluctuations in the edge region accompanied by the formation of the high-density ETB using beam emission spectroscopy (BES), and we compared the behaviour with that of the normal ETB transition of CHS. BES has been implemented in CHS to simultaneously measure both local density fluctuations and gradients. It revealed that the density, density gradient, and inverse value of the density scale length increase in the edge region at both the normal ETB transition and the high-density ETB transition. The turbulence of the frequency at less than 20 kHz is suppressed at the formation of the high-density ETB.
Journal of Physics Conference Series 08/2008; 123(1):012007.
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T Minami,
S Okamura,
T Akiyama,
K Ida,
T Oishi,
M Isobe,
H Nakano,
A Fujisawa,
K Nagaoka,
M Yoshinuma, C Suzuki,
Y Yoshimura,
K Toi,
S Ohshima,
M Takeuchi,
H Iguchi,
S Nishimura,
A Shimizu,
K Matsuoka,
C Takahashi
[show abstract]
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ABSTRACT: Edge transport barrier (ETB) formation and a reheat mode have been simultaneously realized on the Compact Helical System (CHS). The new mode is induced by neutral particle reduction in the edge region, which is caused by shutting off fueling after a strong gas-puffing. When both the reheat mode and the ETB are simultaneously realized, the density reduction is suppressed by the ETB in the peripheral region, and the temperature continues to increase by the reheat mode. This mode provides an enhanced confinement in the high density region (e ~ 1.2 × 1020mr-3) compared to the ETB formation without the reheat mode, because of a large suppression of an anomalous transport, which is confirmed with fluctuation measurements in the edge region.
Journal of Physics Conference Series 08/2008; 123(1):012006.
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K. Nagaoka,
M. Isobe,
K. Toi,
K. Goto,
T. Ito,
Y. Todo,
M. Osakabe,
S. Ohshima,
A. Shimizu,
A. Fujisawa,
H. Nakano,
Y. Takeiri,
K. Y. Watanabe,
T. Akiyama,
Y. Yoshimura, C. Suzuki,
S. Nishimura,
K. Matsuoka,
S. Okamura,
the CHS experimental group
[show abstract]
[hide abstract]
ABSTRACT: Bursting energetic particle mode (EPM) and fast ion loss induced by the EPM have been observed and experimentally investigated in the Compact Helical System (CHS). A directional probe method was newly applied to neutral beam heated plasmas for fast ion measurement, and it successfully revealed fast ion behaviour inside the last closed flux surface (LCFS) during bursting EPMs. A convective oscillation was observed only inside the LCFS, and drives little loss of fast ions. An anomalous loss of fast ions produced by the phase difference between the fast ion oscillation and the EPM with m = 3/n = 2 was observed in the outward shifted configurations. Another anomalous loss of fast ions due to EPMs with m = 2/n = 1 was also observed in the inward shifted configuration. The characteristics of the fast-ion-loss flux are different from those observed in the outward shifted configurations, and the loss mechanism seems to be related to a mode mixture between the EPM and a low frequency mode.
Nuclear Fusion 06/2008; 48(8):084005. · 4.09 Impact Factor
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A. Fujisawa,
K. Itoh,
A. Shimizu,
H. Nakano,
S. Ohshima,
H. Iguchi,
K. Matsuoka,
S. Okamura,
T. Minami,
Y. Yoshimura, [......],
C. Takahashi,
M. Kojima,
S. Nishimura,
M. Isobe, C. Suzuki,
T. Akiyama,
T. Ido,
Y. Nagashima,
S.-I. Itoh,
P. H. Diamond
[show abstract]
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ABSTRACT: The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [
K. Matsuoka, S. Kubo, M. Hosokawa et al., in Plasma Physics and Controlled Nuclear Fusion Research, Proc. 12th Int. Conf., Nice, 1988 (International Atomic Energy Agency, Vienna, 1989, Vol. 2, p. 411
] using twin heavy ion beam probes. The paper presents the experimental observations of stationary zonal flow, nonlinear couplings between zonal flow and turbulence, and the role of zonal flow in the improved confinement, together with the recent discovery of zonal magnetic field. The presented experimental results strongly support the new paradigm that the plasma transport should be considered as a system of drift wave and zonal flows, and provides the first direct evidence for turbulence dynamo that the structured magnetic field can be really generated by turbulence.
Physics of Plasmas 03/2008; 15(5):055906-055906-7. · 2.15 Impact Factor
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H Yamada,
R Sakamoto,
J Miyazawa,
M Kobayashi,
T Morisaki,
S Masuzaki,
S Ohdachi,
M Goto,
K Ida,
S Sakakibara, [......],
M Yokoyama,
S Yoshimura,
M Yoshinuma,
S Imagawa,
O Kaneko,
K Kawahata,
T Mutoh,
N Ohyabu,
A Komori,
O Motojima
[show abstract]
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ABSTRACT: A high density regime with an internal diffusion barrier (IDB) has been extended to the helical divertor (HD) configuration in the Large Helical Device (LHD). Avoidance of the local enhancement of neutral pressure is necessary to enable IDB formation, which is consistent with earlier works by using the Local Island Divertor (LID) with efficient active pumping. The central pressure reached 1.3 times atmospheric pressure, where ne(0) = 6 × 1020 m−3 and Te(0) = 660 eV. The plasmas with an IDB are located in the plateau collisionality regime. The significant impurity effect has not been observed throughout the discharges in spite of the existence of a negative radial electric field. A central pressure limiting event is observed in the plasmas with an IDB using the HD. During this event which is referred to as the core density collapse (CDC), particles are flushed out from the core on the time scale of a few hundreds of microseconds. The suppression of the Shafranov shift by vertical elongation (κ) is effective to mitigate CDC. At κ = 1.2, the central β value is increased up to 6.6% at 1 T.
Plasma Physics and Controlled Fusion 11/2007; 49(12B):B487. · 2.42 Impact Factor
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S Ohshima,
A Fujisawa,
A Shimizu,
H Nakano,
H Iguchi,
Y Yoshimura,
K Nagaoka,
T Minami,
M Isobe,
S Nishimura, [......],
T Akiyama,
C Takahashi,
M Takeuchi,
T Ito,
T Watari,
R Kumazawa,
S-I Itoh,
K Itoh,
K Matsuoka,
S Okamura
[show abstract]
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ABSTRACT: The internal structural measurements of electric field and density using twin heavy ion beam probes have been performed to elucidate the nonlinear evolution of the magneto-hydro-dynamic (MHD) bursty phenomenon driven by the interaction with high-energy particles in a toroidal plasma. The results have given the finest observation of the internal structure of plasma quantities, such as electric field, density and magnetic field distortion, which nonlinearly develop during the MHD phenomenon. In particular, the finding of a new kind of oscillating zonal flow driven by interaction between energetic particles and MHD modes should be emphasized for burning state plasmas.
Plasma Physics and Controlled Fusion 10/2007; 49(11):1945. · 2.42 Impact Factor
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A Fujisawa,
K Itoh,
A Shimizu,
H Nakano,
S Ohshima,
H Iguchi,
K Matsuoka,
S Okamura,
T Minami,
Y Yoshimura, [......],
K Toi,
C Takahashi,
M Kojima,
S Nishimura,
M Isobe, C Suzuki,
T Akiyama,
Y Nagashima,
S-I Itoh,
P H Diamond
[show abstract]
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ABSTRACT: A zonal magnetic field is found in a toroidal plasma. The magnetic field has a symmetric bandlike structure, which is uniform in the toroidal and poloidal directions and varies radially with a finite wavelength of mesoscale, which is analogous to zonal flows. A time-dependent bicoherence analysis reveals that the magnetic field should be generated by the background plasma turbulence. The discovery is classified as a new kind of phenomenon of structured magnetic field generation, giving insight into phenomena such as dipole field generation in rotational planets.
Physical Review Letters 05/2007; 98(16):165001. · 7.37 Impact Factor
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K. Nakamura,
H. Iguchi,
J. Schweinzer,
A. Shimizu,
M. Isobe,
C. Takahashi,
S. Nishimura, C. Suzuki,
Y. Yoshimura,
K. Nagaoka,
T. Minami,
T. Akiyama,
K. Ida,
K. Matsuoka,
S. Okamura
[show abstract]
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ABSTRACT: Two-dimensional edge plasma structures of the l = 2 helical system CHS have been investigated with the use of a neutral lithium beam probe. Two different types of edge magnetic configuration have been compared, namely, an inboard-wall limiter configuration and an ergodic magnetic divertor configuration which is intrinsic to non-axisymmetric helical devices. The scrape-off plasma in the limiter configuration is essentially one-dimensional and the radial scale length is well described by a simple diffusion model with finite connection length of the magnetic field line. While in the ergodic divertor configuration, edge plasma structure shows up–down asymmetry in the steady state near the outer separatrix region regardless of the symmetric magnetic structure. The asymmetry reverses when the magnetic field direction is reversed. Plasma shift is apparently in the direction of ion B × ∇B drift. The result suggests that plasma equilibrium in the ergodic layer is not determined simply by the magnetic field structure. The effect of plasma flow and drift motions would be important. Such asymmetry in plasma structure may induce non-uniform heat deposition on the divertor plates. Modelling of plasma equilibrium in the ergodic layer is necessary for practical helical divertor design.
Nuclear Fusion 03/2007; 47(4):251. · 4.09 Impact Factor
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A Fujisawa,
A Shimizu,
H Nakano,
S Ohshima,
K Itoh,
Y Nagashima,
S-I Itoh,
H Iguchi,
Y Yoshimura,
T Minami, [......],
C Takahashi,
M Kojima,
S Nishimura,
M Isobe, C Suzuki,
T Akiyama,
T Ido,
K Matsuoka,
S Okamura,
P H Diamond
[show abstract]
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ABSTRACT: An extended application of Gabour's wavelet to bicoherence analysis succeeds in resolving the instantaneous structure of three wave couplings between disparate scale electric field fluctuations in the high temperature core in a toroidal plasma device named the compact helical system. The obtained results quantify an intermittent linkage between turbulence and zonal flows—a highlighted issue in the present plasma research. This is the first demonstration that the intermittent nature of the three wave coupling should underlie the turbulence power modulation due to zonal flows.
Plasma Physics and Controlled Fusion 01/2007; 49(3):211. · 2.42 Impact Factor
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T Akiyama,
S Okamura,
T Minami,
A Fujisawa,
T Oishi,
S Kado,
M Takeuchi,
K Toi,
K Ida,
M Yoshinuma,
K Matsuoka,
M Isobe,
S Nishimura, C Suzuki,
Y Yoshimura,
K Nagaoka,
C Takahashi,
the CHS Experimental Group
[show abstract]
[hide abstract]
ABSTRACT: An improved confinement state by the formation of an edge transport barrier can be obtained in the compact helical system. A power threshold exists, as is the case for the H-mode in tokamaks. The threshold scales as . These dependences are similar to those in tokamaks. The threshold also depends on magnetic configuration parameters such as the position of the magnetic axis. The absolute value of the threshold is 1–3 times larger than the tokamak H-mode power scaling.
Plasma Physics and Controlled Fusion 10/2006; 48(11):1683. · 2.42 Impact Factor
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A. Fujisawa,
A Shimizu,
H Nakano,
S. Ohsima,
K Itoh,
H Iguchi,
Y Yoshimura,
T Minami,
K. Nagaoka,
C Takahashi, [......],
M Isobe, C Suzuki,
T Akiyama,
Y Nagashima,
K. Ida,
K. Toi,
T. Ido,
S.-I. Itoh,
K Matsuoka,
S Okamura
[show abstract]
[hide abstract]
ABSTRACT: Turbulence and zonal flow at a transport barrier are studied with twin heavy ion beam probes in a toroidal helical plasma. A wavelet analysis is used to extract turbulence properties, e. g., spectra of both density and potential fluctuations, coherence and phase between them, and the dispersion relation. Particle transport estimated from the fundamental characteristics is found to clearly rise with their intermittent activities after the barrier is broken down. The time-dependent analysis reveals that intermittency of turbulence is correlated with evolution of stationary zonal flow.
Plasma Physics and Controlled Fusion 03/2006; · 2.42 Impact Factor
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S. Okamura,
T. Minami,
T. Akiyama,
T. Oishi,
A. Fujisawa,
K. Ida,
H. Iguchi,
M. Isobe,
S. Kado,
K. Nagaoka, [......],
H. Nakano,
M. Nishiura,
S. Ohshima,
A. Shimizu, C. Suzuki,
C. Takahashi,
K. Toi,
Y. Yoshimura,
M. Yoshinuma,
CHS group
[show abstract]
[hide abstract]
ABSTRACT: Edge transport barrier (ETB) formation was observed in a compact helical system. A sharp decrease in Hα emission indicates the quick transition of edge particle transport. The increase in the density gradient at the edge was measured by using various profile diagnostics. The transition process has a slowly developing pre-phase, and a quick transition for which the fastest case is less than 0.2 ms. There exists a heating power threshold which is roughly proportional to the density and the magnetic field. The transition and back transition is controlled by the heating power. The magnetic configuration effect on ETB formation was also studied. The local density measurement by beam emission spectroscopy shows intermittent bursts of low frequency fluctuations during the ETB formation phase. When the initial density profile is very hollow, ETB formation together with the electron temperature increase (electron internal transport barrier) in the core region, was observed for the NBI discharges without ECH.
Nuclear Fusion 07/2005; 45(8):863. · 4.09 Impact Factor
