Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
Volume 1
Showing 1-50 articles out of 55 articles from the selected issue
Rapid Communications
  • Masaru FURUKAWA, Vinod KRISHAN, Makoto HIROTA, Zensho YOSHIDA
    Type: Rapid Communications
    2006 Volume 1 Pages 001
    Published: 2006
    Released: June 16, 2006
    JOURNALS FREE ACCESS
    The temporal behavior of axisymmetric magneto-rotational instability in a thin accretion disk is analyzed via the Wentzel-Kramars-Brillouin (WKB) method. The height of the thin disk is used as a small parameter. It is found that the oscillation of the envelope of the mode accelerates with time because of the density distribution in the direction of the disk height.
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  • Yoshiro NARUSHIMA, Satoru SAKAKIBARA, Kiyomasa WATANABE, Katsumi IDA, ...
    Type: Rapid Communications
    2006 Volume 1 Pages 004
    Published: 2006
    Released: June 16, 2006
    JOURNALS FREE ACCESS
    A minor collapse observed in current-carrying plasma has been investigated in Large Helical Device (LHD). The magnetic configuration with high central rotational transform has ι/2π = 1 surface at the core region and is relatively unstable for the m/n = 1/1 mode (here, m and n are the poloidal and toroidal mode number, respectively). When the beam-driven current exceeds a certain value, the m/n = 1/1 mode grows with a growth time of ˜30 ms and causes a sudden drop of the plasma stored energy and the electron temperature, and it also limits the plasma current itself. A local flattening in an electron temperature profile appears just after the minor collapse. The mode does not rotate and stays at the same spatial location. The possibility of pressure- and current-driven magneto-hydro dynamics (MHD) instabilities is discussed.
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  • Kenichi NAGAOKA, Mitsutaka ISOBE, Kouji SHINOHARA, Masaki OSAKABE, Aki ...
    Type: Rapid Communications
    2006 Volume 1 Pages 005
    Published: 2006
    Released: June 16, 2006
    JOURNALS FREE ACCESS
    A directional Langmuir probe (DLP) method has been applied to measurement of energetic particles (ions) in a magnetically confined plasma. Two experimental demonstrations were performed in the compact helical system (CHS). One was a neutral beam modulation experiment and the other was the measurement of energetic ion loss induced by MHD bursts. The results of the DLP were consistent with those of a neutral particle analyzer (NPA) and a lost ion probe (LIP). These experiments show that this method is applicable outside and also inside the last closed flux surface.
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  • Zensho YOSHIDA, Yuichi OGAWA, Junji MORIKAWA, Sho WATANABE, Yoshihisa ...
    Type: Rapid Communications
    2006 Volume 1 Pages 008
    Published: 2006
    Released: June 29, 2006
    JOURNALS FREE ACCESS
    The first plasma experiment using the Ring Trap-1 (RT-1) was performed on January 12, 2006. The RT-1 is a novel plasma device constructed to explore ways to the advanced-fuel fusion. The mechanism of plasma confinement is based on the theory of high-beta equilibrium that is self-organized in a flowing plasma. A superconducting ring, levitated in the vacuum chamber, produces a magnetic field that traps high-temperature plasma, creating a magnetosphere-like configuration. Plasma is produced by electron cyclotron heating using an 8.2 GHz microwave.
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  • Yuji NAKAMURA
    Type: Rapid Communications
    2006 Volume 1 Pages 010
    Published: 2006
    Released: June 29, 2006
    JOURNALS FREE ACCESS
    The effects of toroidal field ripples on bootstrap current in the low collisionality regime in tokamak plasmas are discussed by using an asymptotic expression of the bootstrap current. When the toroidal field ripple is 1-3%, an 8-15% reduction of the bootstrap current is predicted in a tokamak plasma having q = 1.8 and εt = 0.3. If we fix the ripple ratio, dependence on the number of toroidal field coils is negligible when the number is more than 15. These results suggest that the effect of the toroidal field ripple on the bootstrap current is particularly important when the pressure gradient is steep near the plasma edge.
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  • Taiki YAMAGUCHI, Kiyomasa WATANABE, Satoru SAKAKIBARA, Yasuhiro SUZUKI ...
    Type: Rapid Communications
    2006 Volume 1 Pages 011
    Published: 2006
    Released: June 29, 2006
    JOURNALS FREE ACCESS
    A new calibration method for evaluating equilibrium parameters such as the beta value and its radial profile is introduced. The method is based on a real-coordinate equilibrium code (HINT), which does not assume nested flux surfaces, and on a signal-analysis code (JDIA), which evaluates the flux of magnetic measurements from the result of the HINT. Results of the present work are closer to experimental data than results of a conventional method which assumes nested flux surfaces.
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  • Yoshiyuki TAKAHASHI, Tomohiro MORISAKI, Kazuo TOI, LHD Experimental G ...
    Type: Rapid Communications
    2006 Volume 1 Pages 013
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    In the Large Helical Device (LHD), of which the magnetic surfaces are surrounded by an ergodic magnetic field layer, the two-dimensional prole of electron density was for the first time measured by a newly developed sheet-shaped thermal lithium beam probe. The sheet beam was formed by guiding lithium vapor through three orifices placed in front of an aperture of an oven and injecting the vapor nearly vertically into the LHD plasma. The two-dimensional (2D) image of the LiI line was measured by using a CCD camera with an interference filter for LiI (670.8 nm). From the 2D image of LiI, we successfully obtained a two-dimensional profile of electron density in the plasma edge region.
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  • Takashi SUMIKAWA, Kouhei YAMASHITA, Manabu ONODA, Tokihiko TOKUZAWA, E ...
    Type: Rapid Communications
    2006 Volume 1 Pages 014
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    Two-Dimensional Thomson Scattering Measurement (2-D TS) was designed using multiple reflections and the time-of-flight of laser light. This new approach enable us to measure the r(radial)-z(axial) profiles of electron temperature and density. In this approach, (1) multiple reflections of YAG laser light are used to cover the whole r-z plane of the ST (Spherical Tokamak) plasma, and (2) the time delay of the scattered light along the laser beam is arbitrarily arranged by adjusting the multiply reflected laser light path in order to reduce the necessary number of detectors. Rayleigh scattering lights were observed successfully at two measurement points, suggesting that the basic principle of the 2-D Thomson scattering system functions effectively as a new extension of LIDAR (LIght Detection And Ranging) Thomson scattering system.
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  • Tomoya TATSUNO, William DORLAND
    Type: Rapid Communications
    2006 Volume 1 Pages 015
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    An ideal magnetohydrodynamic instability which is driven by sheared flow and which may be relevant to reversed-shear advanced tokamak operation is described. If there is flow shear at the qmin surface, relatively weak velocity shear can drive this instability, with a time scale of the flow. The flows may be signicantly slower than the ambient poloidal Alfvén velocity, and no inflection point is needed. Thus the time scale of the instability may be signicantly longer than that of the poloidal Alfvén transit time, and it might account for disruption of reversed-shear discharges recently observed in JT-60U.
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  • Hirokazu OHWAKI, Masayoshi SUGIHARA, Akiyoshi HATAYAMA
    Type: Rapid Communications
    2006 Volume 1 Pages 016
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    A numerical model is developed to evaluate the decay time of plasma current during the disruption following intense impurity injections. Our model is based on the power balance equation between joule heating and impurity radiation as a way to evaluate the electron temperature and charge state after the thermal quench. The model is applied to the experimental results of massive N2 gas injections in JFT-2M, which simulate the “ingress-of-coolant event” (ICE) as well as disruption mitigations in ITER. It is confirmed that the model can reproduce the experiments reasonably well.
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  • Hitoshi HOJO, Kazuhiro AKIMOTO
    Type: Rapid Communications
    2006 Volume 1 Pages 018
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    The transmission of electromagnetic waves across a thin plasma layer whose width is comparable to the wavelength of an incident wave is studied. The transmittances of transverse electric and transverse magnetic modes for both underdense and overdense plasmas are obtained as a function of the angle of incidence. It is thought that the significant reduction of transmittance in overdense plasma's transverse magnetic modes is caused by the excitation of the electron plasma wave on the plasma resonance layer.
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  • Ryuichi SAKAMOTO, Suguru MASUZAKI, Junichi MIYAZAWA, LHD Experimental ...
    Type: Rapid Communications
    2006 Volume 1 Pages 019
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    A high-luminosity striation, which rotates within a flux surface of the plasma boundary having helical structure, has been observed in the LHD plasmas by means of a fast camera. The striation appears when the plasma is shrinking due to excessive gas fueling despite the existence of neutral beam heating.
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  • Hitoshi HOJO, Naoto UCHIDA, Kunihiko HATTORI, Atsushi MASE
    Type: Rapid Communications
    2006 Volume 1 Pages 021
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    The beaming of millimeter waves from two-dimensional plasma photonic crystal waveguides is studied numerically based on a finite difference time domain simulation. It is shown that the beaming of millimeter waves is due to coupling with surface lattice modulation in plasma photonic crystals having a glass-rod lattice in the background discharged plasma, while millimeter-wave beaming is due to the horn antenna of plasma rods in plasma photonic crystals having a plasma-rod lattice in a vacuum.
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  • Toshiki TAKAHASHI, Naotaka IWASAWA, Takayuki KATO, Yoshiomi KONDOH
    Type: Rapid Communications
    2006 Volume 1 Pages 022
    Published: 2006
    Released: July 28, 2006
    JOURNALS FREE ACCESS
    An axially expanding motion of a field-reversed configuration plasma can be observed numerically. This motion is induced by fast ions reciprocating between field-null x-points; the ions are injected obliquely from the axial end as neutral beam particles. A two-dimensional hybrid simulation is employed by assuming axisymmetry, where the beam ions are treated as particles and the plasma ions and electrons are treated as fluid. The diamagnetic beam current formed around the x-points and in the open-field region reduces the magnetic pressure, and then the plasma is found to expand axially.
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  • Kazumichi NARIHARA, Ryuichi SAKAMOTO, Ichihiro YAMADA, Hisamichi FUNAB ...
    Type: Rapid Communications
    2006 Volume 1 Pages 023
    Published: 2006
    Released: July 28, 2006
    JOURNALS FREE ACCESS
    We present a particle transport phenomenon caused by a hydrogen ice pellet injection (PI) into the Large Helical Device. The electron density (ne) profile evolution after a PI was measured by using a 200-channel Thomson scattering diagnostic. The highly hollow ne-profile caused by a PI faded out as time elapsed with a very slight increase in the ne at the core region, giving a direct evidence for the inward electron flux being almost completely blocked in the core region.
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  • Osamu WATANABE, Tsuguhiro WATANABE, Kazuo OGURA, Tsuyoshi IMAI, Teruji ...
    Type: Rapid Communications
    2006 Volume 1 Pages 025
    Published: 2006
    Released: July 28, 2006
    JOURNALS FREE ACCESS
    The dispersion characteristics of surface wave propagated on a deeply corrugated metal surface are analyzed. Surface wave becomes slow wave, because surface wave is evanescent wave to the direction away from the corrugated metal surface. The surface wave is possible to be backward wave, due to the periodic nature of the corrugation of metal surface. Because the Rayleigh hypothesis has failed for the analysis of an electromagnetic field upon a deeply corrugated surface, the dispersion relations are solved by a direct numerical computation of wave equations.
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  • Masaki TAKEUCHI, Kazuo TOI, Kenichi NAGAOKA, Chihiro SUZUKI, Takashi M ...
    Type: Rapid Communications
    2006 Volume 1 Pages 027
    Published: 2006
    Released: July 28, 2006
    JOURNALS FREE ACCESS
    The structure of the Edge Transport Barrier (ETB) was measured by means of a triple Langmuir probe in the Compact Helical System, this diagnostic method achieving high time and spatial resolutions. The radial profiles of electron temperature and electron density show a steep gradient inside the normalized minor radius ρ ˜ 0.96, having a plateau of Te at 0.96 < ρ < 1 and a dip of ne at 0.95 < ρ < 0.98. The radial electric field clearly changed in the H-phase in the region at ρ < 0.96 and 0.99 < ρ < 1, and its shear increased around ρ ˜ 0.97. The characteristic profile evolutions suggest an interaction between ETB formation and a magnetic island related to ι/(2π) = 1. Based on these data, the precise position of the ETB is not determined denitely; that is, it is not established whether it exists inside the magnetic island or closely inside the last closed flux surface (ρ = 1).
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  • Yasuo YOSHIMURA, Kazunobu NAGASAKI, Tsuyoshi AKIYAMA, Mitsutaka ISOBE, ...
    Type: Rapid Communications
    2006 Volume 1 Pages 029
    Published: 2006
    Released: August 10, 2006
    JOURNALS FREE ACCESS
    An evident increase in the plasma stored energy by applying 54.5 GHz electron cyclotron (EC) waves has been observed in plasmas sustained by neutral beam injection (NBI) with line-averaged electron density of above 3.8 × 1019 m-3, that is, the cut-off density of the 54.5 GHz waves, in the Compact Helical System (CHS). The heating effect can be seen even for high-density over 8 × 1019 m-3: more than twice the cut-off density. The 54.5 GHz EC-wave beam is obliquely injected to high-density plasmas. The scanning of the EC-wave beam direction gives the evident increase in the stored energy at the beam direction where the leakage EC-wave power from the CHS vacuum vessel becomes almost the minimum. The most possible cause for this heating mechanism is an electron Bernstein wave heating via an Ordinary - eXtraordinary - Bernstein (O-X-B) mode conversion process.
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  • Akihiko ISAYAMA, Naoyuki OYAMA, Hajime URANO, Takahiro SUZUKI, Manabu ...
    Type: Rapid Communications
    2006 Volume 1 Pages 030
    Published: 2006
    Released: August 10, 2006
    JOURNALS FREE ACCESS
    Growth of a neoclassical tearing mode (NTM) with a poloidal mode number m = 3 and a toroidal mode number n = 2 has been controlled by electron cyclotron current drive (ECCD) in the same direction as the plasma current (co-ECCD) in the central region away from the NTM island. By using ECCD at a fraction of about 10% of the plasma current, the amplitude of the m/n = 3/2 NTM is limited to about 1/5 of that without ECCD. The frequency spectrum of magnetic perturbations shows that the frequency of the m/n = 3/2 NTM is modulated by a sawtooth crash. The beta value, which is the ratio of the plasma pressure to the magnetic pressure, is higher by 6% than that without ECCD at the same input power. This operational scenario is quite different from that for conventional NTM stabilization in which the ECCD location is accurately adjusted at the mode rational surface and is thus off-axis. This result shows the compatibility of sawtooth oscillations and a small-amplitude 3/2 NTM, and suggests the possibility of a new and easier operational scenario for NTM control.
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  • Hiroyuki HIGAKI, Makoto ICHIMURA, Daisuke INOUE, Ken-ichiro NAKAGOME, ...
    Type: Rapid Communications
    2006 Volume 1 Pages 034
    Published: 2006
    Released: September 01, 2006
    JOURNALS FREE ACCESS
    Alfvén eigen modes were observed in the Large Helical Device for various magnetic field strengths and plasma densities. It was found that Alfvén eigen modes could be excited at much higher frequencies (0.5 ˜ 2.5 MHz) and higher magnetic fields (1.5 ˜ 2.83 T) than previously reported. A part of the estimated Alfvén velocities (2 ˜ 6 × 107 m/s) exceeded the thermal velocity of injected neutral beams (˜ 4.1 × 106 m/s).
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  • Nobuhiro NISHINO, Yousuke NAKASHIMA, Yuta HIGASHIZONO, Shinji KOBAYASH ...
    Type: Rapid Communications
    2006 Volume 1 Pages 035
    Published: 2006
    Released: September 01, 2006
    JOURNALS FREE ACCESS
    Visible imaging measurement using a fast camera in conjunction with a gas puff was demonstrated in the GAMMA 10 tandem mirror. In order to image plasma behavior on the periphery, a hydrogen gas puff in the bottom of the vacuum chamber near the GAMMA 10 central-cell was used. Without the gas puff the light emission was not sufficiently bright, and SN ratio is not good. By using the gas puff, the light emission could be clearly observed, and a 5 - 6 kHz vibration of the plasma column was confirmed. This motion is most likely plasma rotation due to the electron drift wave and Er × B drift. These results show that the fast camera used in conjunction with a gas puff is a promising candidate for the measurement of peripheral plasma behavior even in low-density mirror plasmas.
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  • Kimitaka ITOH, Sanae-I. ITOH, Patrick H. DIAMOND, Akihide FUJISAWA, Ma ...
    Type: Rapid Communications
    2006 Volume 1 Pages 037
    Published: 2006
    Released: September 01, 2006
    JOURNALS FREE ACCESS
    The eigenmode of a geodesic acoustic mode in the presence of a temperature gradient is discussed. Eigenmodes are obtained and the characteristic wavelength scales as ρi2/3LT1/3i: ion gyroradius, LT: temperature gradient scale length). The direction of propagation is discussed.
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  • Youichi SAKAWA, Kazuyoshi SUGIYAMA, Tetsuo TANABE, Richard MORE
    Type: Rapid Communications
    2006 Volume 1 Pages 039
    Published: 2006
    Released: September 01, 2006
    JOURNALS FREE ACCESS
    Fireball generation in a water discharge has been investigated. Time evolution of visible spectra of the fireballs revealed that the emission of ionic lines of Ca and atomic lines of Na, K, Li, and Ca appeared early in time, followed by un-identified molecular-like spectra, and the emission of NaI resonance lines (588.9 and 589.5 nm), remained at the final stage of the fireball.
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  • Yuya YOKOTA, Atsushi MASE, Yuichiro KOGI, Tokihiko TOKUZAWA, Kazuo KAW ...
    Type: Rapid Communications
    2006 Volume 1 Pages 040
    Published: 2006
    Released: October 26, 2006
    JOURNALS FREE ACCESS
    An ultrashort-pulse reflectometer (USPR) has been applied to the measurement of the edge density profile of the Large Helical Device at the National Institute for Fusion Science. The reflectometer signal is recorded directly using a high-speed digitizing scope, and is analyzed by means of a signal record analysis method to reconstruct the density profiles. This method has the advantage of using raw signal records instead of poorly localized frequency modes. The density profiles in the edge region are successfully determined and compared with those obtained by an FIR laser interferometer.
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  • Yoshiomi KONDOH, Toru HAKOIWA, Akihito OKADA, Naohiro KOBAYASHI, Toshi ...
    Type: Rapid Communications
    2006 Volume 1 Pages 043
    Published: 2006
    Released: October 26, 2006
    JOURNALS FREE ACCESS
    A novel set of simultaneous eigenvalue equations having dissipative terms are derived to find self-similarly evolving and minimally dissipated stable states of plasmas realized after relaxation and self-organization processes. By numerically solving the set of eigenvalue equations in a cylindrical model, typical spatial profiles of plasma parameters, electric and magnetic fields and diffusion factors are presented, all of which determine self-consistently with each other by physical laws and mutual relations among them, just as in experimental plasmas.
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  • Daiju FUJITA, Yasuhito KIWAMOTO, Yukihiro SOGA, Nobuya HASHIZUME
    Type: Rapid Communications
    2006 Volume 1 Pages 044
    Published: 2006
    Released: October 26, 2006
    JOURNALS FREE ACCESS
    Accelerated deformations are observed in the density distribution of a pure electron plasma that is weakly diocotron-unstable when l clumps are introduced along a circle where the rotation frequency advected by the target plasma is close to the phase-rotation frequency of an unstable wave with the mode number of l. When the advection frequency is not close to the phase frequency, the clumps are modified in their orbit by the most unstable wave of the target plasma and bunched azimuthally into the distribution modulated by the wave.
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  • Takashi MINAMI, Shoichi OKAMURA, Tsuyoshi AKIYAMA, Mitsutaka ISOBE, Te ...
    Type: Rapid Communications
    2006 Volume 1 Pages 047
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    An improved confinement mode with reheat and edge transport barrier is observed in the Compact Helical System (CHS). This mode provides enhanced confinement in high density region (ne ˜ 1.2 × 1020 m-3) due to the increase in temperature while high density is maintained in the peripheral region.
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  • Etsuo FUJIWARA, Keiichi NISHIKAWA, Michiharu KIRINUKI, Kingo AZUMA, Mi ...
    Type: Rapid Communications
    2006 Volume 1 Pages 048
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    A bright optical emission inside a trench in a solid object was observed during a diamond-like carbon (DLC) deposition process, with the DLC deposition rate being more than two-times faster on the trench's bottom than that on the top of the trench. We found that the secondary electrons inside the trench played an important role in the higher DLC deposition rate on the trench's bottom.
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  • Shuichi TAKAMURA, Noriyasu OHNO, Dai NISHIJIMA, Shin KAJITA
    Type: Rapid Communications
    2006 Volume 1 Pages 051
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    Deeply nanostructured tungsten with an arborescent shape was found for the first time to be formed on tungsten-coated graphite by a high-flux helium plasma irradiation at surface temperatures of 1250 and 1600 K, an incident ion energy of 12 eV (well below the physical sputtering threshold) and a helium ion fluence of 3.5 × 1027 m-2.
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  • Hiroe IGAMI, Takashi SHIMOZUMA, Shin KUBO, Kazunobu NAGASAKI, Shigeru ...
    Type: Rapid Communications
    2006 Volume 1 Pages 052
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    In a magnetic field configuration of the Large Helical Device (LHD), when the extraordinary mode (X-mode) waves are obliquely injected from a bottom antenna, it can directly access the upper hybrid resonance (UHR) layer from the high field side and excite electron Bernstein waves (EBWs) without the need for any additional reflecting mirror antenna. A localized power absorption is observed in the low field side of the electron cyclotron resonance (ECR) layer. This result suggests electron cyclotron heating (ECH) by mode converted EBWs excited via X-B mode conversion process.
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  • Filippo SCOTTI, Shinichiro KADO, Atsushi OKAMOTO, Taiichi SHIKAMA, Sat ...
    Type: Rapid Communications
    2006 Volume 1 Pages 054
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    Laser Thomson Scattering (LTS) measurements of Electron Ion Recombining (EIR) Helium plasma were performed in the divertor/edge simulator MAP-II. Upgrades of our LTS system, in the stray-light level and in the notch filter, allowed the measurement of electron temperatures as low as 0.1 eV and further investigation of EIR processes. Electron temperature and electron density profiles of EIR He recombining plasmas with different background neutral pressures have been measured.
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  • Etsuo FUJIWARA, Hiroki SUGISHITA, Yasuhiro OKABE, Mitsuyasu YATSUZUKA, ...
    Type: Rapid Communications
    2006 Volume 1 Pages 055
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    A new flow control method for a tin droplet generator in a vacuum has been developed for Extreme Ultra-Violet Lithography. A vibration rod forced by a piezoelectric crystal varies the flow resistance, thus changing the flow rate at a high repetition rate. This droplet generator is advantageous for high temperature liquids such as molten metal. The formation of tin droplets using this generator was demonstrated at a frequency range of 10 kHz to 22 kHz by a 100 m nozzle.
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Letters
  • M. Abdur RAZZAK, Shuichi TAKAMURA, Noriyasu OHNO
    Type: Letters
    2006 Volume 1 Pages 006
    Published: 2006
    Released: June 16, 2006
    JOURNALS FREE ACCESS
    The effects of using an array of tungsten pin electrodes on the ignition dynamics of radio frequency (rf) discharges generated by inductively coupled plasma (ICP) technique at atmospheric pressure are investigated experimentally. The experimental observations reveal that the array of tungsten pin electrodes successfully enhance the initial discharges maintained by the strong electrostatic field with stable and fast ignition, which enables us to sustain efficient rf induction plasmas at atmospheric pressure range.
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  • Ken UZAWA, Yasuaki KISHIMOTO, Jiquan LI
    Type: Letters
    2006 Volume 1 Pages 024
    Published: 2006
    Released: July 28, 2006
    JOURNALS FREE ACCESS
    The effects of an external mean flow on the generation of zonal flow in drift wave turbulence are theoretically studied in terms of a modulational instability analysis. A dispersion relation for the zonal flow instability having complex frequency ωq = Ωq + iγq is derived, which depends on the external mean flow's amplitude |φf| and radial wave number kf. As an example, we chose an ion temperature gradient (ITG) turbulence-driven zonal flow as the mean flow acting on an electron temperature gradient (ETG) turbulence-zonal flow system. The growth rate of the zonal flow γq is found to be suppressed, showing a relation γq = γq0(1-α|φf|2kf2 ), where γq0 is the growth rate in the absence of mean flow and α is a positive numerical constant. This formula is applicable to a strong shearing regime where the zonal flow instability is stabilized at α|φf2|kf2 ≈ 1. Meanwhile, the suppression is accompanied by an increase of the real frequency |Ωq|. The underlying physical mechanism of the suppression is discussed.
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  • Kichiro SHINYA
    Type: Letters
    2006 Volume 1 Pages 036
    Published: 2006
    Released: September 01, 2006
    JOURNALS FREE ACCESS
    Factors that dominate achievement of the decay-index (or N-index) distribution required for highly elongated divertor plasmas with large triangularity are studied. The outermost coil is regarded as a leading candidate, but can supply only a part of the equilibrium value. Current in Central Solenoid with the same direction as the outermost coil current is found to fill the difference of the decay-index distribution on the mid-plane between the equilibrium magnetic field and the outermost coil field.
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  • Satoru SAKAKIBARA, Kiyomasa WATANABE, Hiroshi YAMADA, Yoshiro NARUSHIM ...
    Type: Letters
    2006 Volume 1 Pages 049
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    The relationship between magnetohydrodynamic (MHD) modes and the linear stability boundary has been investigated by controlling the pressure gradient in the Large Helical Device. Edge plasma pressure was varied by inserting a pump limiter into the plasma, and the onsets of MHD modes were determined. A quantitative comparison between mode onsets and a linear stability index of the resistive interchange mode was performed under the condition of a specific magnetic Reynolds number. The experimental results are consistent within a factor of 2 with a rough estimation of the stability boundary of a resistive low-n mode.
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  • Yasuo YOSHIMURA, Kazunobu NAGASAKI, Tsuyoshi AKIYAMA, Mitsutaka ISOBE, ...
    Type: Letters
    2006 Volume 1 Pages 053
    Published: 2006
    Released: December 28, 2006
    JOURNALS FREE ACCESS
    Evident increases in plasma stored energy have been observed in the Compact Helical System (CHS) by injecting nearly X-mode-polarized 54.5 GHz electron cyclotron (EC) waves from the high-field side. An additional plane mirror that enabled the high-field side injection of the EC waves was installed. The centrally peaked and increased electron temperature distributions with the X-mode wave directions which are not aimed at the fundamental resonance layer at the plasma core region strongly suggest that the heating effects occurred due to the excitation of the electron Bernstein waves via mode conversion from the X-mode waves injected from the high-field side.
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Regular Articles
  • Shinsuke SATAKE, Masao OKAMOTO, Noriyoshi NAKAJIMA, Hideo SUGAMA, Masa ...
    Type: Regular Articles
    2006 Volume 1 Pages 002
    Published: 2006
    Released: June 16, 2006
    JOURNALS FREE ACCESS
    Neoclassical transport simulation code (FORTEC-3D) applicable to non-axisymmetric configurations is developed. A new hybrid simulation model in which ion transport is solved by using the δf Monte-Carlo method including the finite-orbit-width effects, while electron transport is solved by a reduced ripple-averaged kinetic equation, is adopted. This model makes it possible to simulate the dynamism of non-local transport phenomena with a self-consistently developing radial electric field within an allowable computation time. Time evolution of a radial electric field in LHD plasma is simulated in the full volume of the confinement region, and the finite-orbit-width effect of neoclassical transport is found to make the negative ambipolar electric field larger than that predicted by local transport theory.
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  • Satoru SAKAKIBARA, Kiyomasa WATANABE, Hiroshi YAMADA, Yoshiro NARUSHIM ...
    Type: Regular Articles
    2006 Volume 1 Pages 003
    Published: 2006
    Released: June 16, 2006
    JOURNALS FREE ACCESS
    The effects of resonant magnetic fluctuations on plasma confinement have been investigated in current carrying high-β plasmas in magnetic hill configurations of the Large Helical Device. The m/n= 2/1 mode excited in core region was dominantly observed in the unstable configuration as predicted by linear theory on ideal instability, and the plasma current decreasing magnetic shear enhances the mode activity. The disappearance of the m/n = 2/1 mode was observed with an increase in plasma current, and then the plasma confinement and the beta value increase by less than 10 % with the recovery of core pressure. When the plasma current exceeds a certain value, the plasma confinement is improved by 20 % with the reduction of the amplitudes of the modes in the peripheral region in addition to the disappearance of the m/n = 2/1 mode. Then the beta value increases by 38 %. MHD activities led to no disruption even in such an unstable configuration, and the moderate plasma current mitigated the effect of MHD activity on the plasma confinement.
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  • Kouji SHINOHARA, Yutaka SUZUKI, Shinji SAKURAI, Kei MASAKI, Takaaki FU ...
    Type: Regular Articles
    2006 Volume 1 Pages 007
    Published: 2006
    Released: June 29, 2006
    JOURNALS FREE ACCESS
    The design process regarding ferritic insertion in the JT-60U is described from the viewpoint of the behavior of energetic ions. The confinement of energetic ions and the absence of unfavorable heat flux on the first wall were assessed using the Fully Three-Dimensional magnetic field OFMC code, which was developed for the toroidal field ripple reduction experiment program utilizing ferritic inserts in the JFT-2M. In the final design, the absorbed power in the neutral beam injection is improved by a factor of about 1.3 in a large volume plasma with Bt0 = 1.9 T.
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  • Hiroki MATSUNO, Shuichi TAKAMURA, Shun HOSOI, Noriyasu OHNO
    Type: Regular Articles
    2006 Volume 1 Pages 009
    Published: 2006
    Released: June 29, 2006
    JOURNALS FREE ACCESS
    A new analysis of meander-line type antenna with dielectric cover is presented and compared with experimental results. In the case of small research tokamaks for which the lower hybrid range of frequency is relatively low, a meander-line antenna with a strip-line structure would be preferable for LHW electron heating. When the antenna is installed in the vacuum chamber, it needs an insulating cover to protect it from plasma bombardment. The comparison between the analysis and experiments agree well if the thickness of the antenna conductor is sufficiently thin and there is no vacuum gap among the substrate, conductor, and cover. We found that a slow-wave antenna may be fabricated for LHW electron heating in the small tokamak HYBTOK-II under the driving frequency of, for example, 220 MHz.
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  • Ryutaro KANNO, Shinsuke SATAKE, Masanori NUNAMI
    Type: Regular Articles
    2006 Volume 1 Pages 012
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    In fluid equations describing edge plasma transport, the fluctuating flow causing anomalous transport is frequently interpreted as noise. The transport which is generated by the noise is represented as diffusion. In the present paper, the validity of the anomalous diffusion model of the fluctuating flow, i.e., Γa = -Da • ∇v, is examined from the viewpoint of a stochastic approach to modeling, where v is a velocity field and Da is a tensor of an anomalous diffusion coefficient. The examination is carried out on the presupposition that the validity of the diffusion model itself is not strongly related to details of the edge plasma. If the diffusion model is derived directly from the fundamental properties of the fluctuating flow, then the model is understood to be not merely an approximate description of the anomalous transport but to be inherent in the transport. However, it is found that because the noise given from the fluctuating flow is essentially bounded, the transport modeling is not justied.
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  • Koichi HATA, Masahiro SHIOTSU, Nobuaki NODA
    Type: Regular Articles
    2006 Volume 1 Pages 017
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    The subcooled flow boiling critical heat fluxes (CHFs) and the heat transfer coefficients (HTCs) data for the tube length, L, of 49, 99 and 149 mm with 9-mm inner diameter were applied to thermal analysis on the Mono-block type divertor of LHD. Incident CHFs for the divertor with the cooling tube diameter, d, of 10 mm and the carbon armor outer diameter, D, of 26 and 33 mm were numerically analyzed based on the measured CHFs and HTCs at the inlet pressure of around 800 kPa. The numerical solutions were also compared with those for the Flat-plate type divertor, which were numerically analyzed for the divertor with the cooling tube diameter d=10 mm and the divertor width, w, ranging from 16 to 30 mm. It is confirmed that the ratio of the one-side heating CHF data, qcr,inc, to the uniform heating CHF data, qcr,sub, can be represented as the simple equation based on the numerical solutions. The values of the qcr,inc for L=50, 100 and 150 mm were estimated with various D/d and w/d at higher pressures.
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  • Akiro HATA, Kunioki MIMA, Astushi SUNAHARA, Hideo NAGATOMO, Akio NISHI ...
    Type: Regular Articles
    2006 Volume 1 Pages 020
    Published: 2006
    Released: July 27, 2006
    JOURNALS FREE ACCESS
    The generalized temporal evolution equation of a magnetic field is derived for high density laser-fusion plasmas. Magnetic field generation and convection are simulated by using the 2D hydrodynamic code together with the magnetic field equation. It is found that magnetic fields are generated and compressed in association with the Rayleigh-Taylor instability of an imploding shell. In particular, the magnetic field convection by the Nernst effect is found to play an important role in the amplification of magnetic fields. The maximum magnetic field reaches 30 MG at maximum compression. This magnetic field may reduce the electron heat conduction around the hot spark. Therefore, it is concluded that the ignition condition for non-uniform implosion is influenced by self-generated magnetic fields.
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  • Junichi MIYAZAWA, Suguru MASUZAKI, Motoshi GOTO, Naoki TAMURA, Ryuichi ...
    Type: Regular Articles
    2006 Volume 1 Pages 026
    Published: 2006
    Released: July 28, 2006
    JOURNALS FREE ACCESS
    In the Large Helical Device (LHD), the hot plasma column shrinks at the high-density regime and complete detachment takes place. Hydrogen volume recombination is observed at complete detachment. This phase is self-sustained under specific experimental conditions and called the Serpens mode (self-regulated plasma edge ‘neath the last-closed-flux-surface). The Serpens mode is achieved after either rapid or slow density ramp up, and either by hydrogen or helium gas puffing. The threshold conditions for complete detachment and the Serpens mode are experimentally documented in the parameter space of heating power and density. The threshold density for the Serpens mode transition increases with ˜ 0.4 power of the heating power. The total radiation is shown to be not adequate to describe the threshold conditions, since it mainly includes the information of very edge region outside the hot plasma column. The operational density limit in LHD, which is sustainable in steady state, has been extended to 1.7 times as high as the Sudo density limit, by applying pellet injection to the Serpens plasmas.
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  • Noriyasu OHNO, M. Abdur RAZZAK, Hiroshi UKAI, Shuichi TAKAMURA, Yoshih ...
    Type: Regular Articles
    2006 Volume 1 Pages 028
    Published: 2006
    Released: August 10, 2006
    JOURNALS FREE ACCESS
    The validity of electron temperature measurement using the Boltzmann plot method was investigated in a radio frequency (rf) inductive discharge in the atmospheric pressure range. Since the Boltzmann plot method requires local thermal equilibrium (LTE), the parameter regions of electron temperature and electron density, in which the Boltzmann plot method is applicable, were analyzed in terms of a comparison of the spontaneous emission and collisional excitation to the excited states. It is observed that in our rf-inductive plasma near the atmospheric pressure range the Boltzmann plot method does not provide an exact measurement of electron temperature because of relatively low electron density, which does not satisfy the calculation criteria. An alternative method employing a combination of the Stark broadening measurement and the Saha-Boltzmann equation was demonstrated to more accurately determine the plasma parameters (electron temperature and electron density).
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  • Hisato KAWASHIMA, Katsuhiro SHIMIZU, Tomonori TAKIZUKA, Shinji SAKURAI ...
    Type: Regular Articles
    2006 Volume 1 Pages 031
    Published: 2006
    Released: August 10, 2006
    JOURNALS FREE ACCESS
    An integrated SOL/divertor code is being developed by the JAEA (Japan Atomic Energy Agency) for interpretation and prediction studies of the behavior of plasmas, neutrals, and impurities in the SOL/divertor region. A code system consists of the 2D fluid code for plasma (SOLDOR), the neutral Monte-Carlo code (NEUT2D), the impurity Monte-Carlo code (IMPMC), and the particle simulation code (PARASOL). The physical processes of neutrals and impurities are studied using the Monte Carlo (MC) code to accomplish highly accurate simulations. The so-called divertor code, SOLDOR/NEUT2D, has the following features: 1) a high-resolution oscillation-free scheme for solving fluid equations, 2) neutral transport calculation under the condition of fine meshes, 3) successful reduction of MC noise, and 4) optimization of the massive parallel computer. As a result, our code can obtain a steady state solution within 3 ˜ 4 hours even in the first run of a series of simulations, allowing the performance of an effective parameter survey. The simulation reproduces the X-point MARFE (multifaceted asymmetric radiation from edge) in the JT-60U. It is found that the chemically sputtered carbon at the dome causes radiation peaking near the X-point. The performance of divertor pumping in the JT-60U is evaluated based on particle balances. In regard to the divertor design of the next tokamak of JT-60U, the simulation indicates the dependencies of pumping effciency on the divertor geometry and operational conditions. The effciency is determined by the balance between the incident and back-flow fluxes into and from the exhaust chamber.
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  • Takashi MINAMI, Shoichi OKAMURA, Tsuyoshi AKIYAMA, Mitsutaka ISOBE, Te ...
    Type: Regular Articles
    2006 Volume 1 Pages 032
    Published: 2006
    Released: August 10, 2006
    JOURNALS FREE ACCESS
    An edge transport barrier (ETB) similar to the tokamak H-mode has been observed for beam-heated plasma with two co-injected Neutral Beam Injectors (NBIs) in CHS. The Hα emission showed a clear spontaneous drop followed by an increase of line-averaged electron density at the L-H transition. Stored energy increased by ˜ 40% with H-factor improvement up to ˜ 30% compared to the international stellarator scaling (ISS04v03). A rapid density increase in the edge region to two-times level of the L-mode was observed to accompany a ˜ 15% increase in the density gradient. An ETB was formed when the plasma density exceeded the lower density limit by ˜ 1.5 × 1013 cm-3 and the total NBI power exceeds the threshold level (Pdeposit / ne ˜ 200 × 10-13 kW/cm-3 at BT = 0.95 T, Rax = 92.1 cm, where Pdeposit is the deposited NBI power, ne is electron density, BT is troidal magnetic field strength and Rax is location of magnetic axis). The power threshold increased with the magnetic field strength, as in tokamak scaling, and depends on the magnetic field configuration of the helical plasma.
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  • Mitsuyasu HOSHINO, Ryuichi SAKAMOTO, Hiroshi YAMADA, Tokihiko TOKUZAWA ...
    Type: Regular Articles
    2006 Volume 1 Pages 033
    Published: 2006
    Released: August 10, 2006
    JOURNALS FREE ACCESS
    Ablation of a solid hydrogen pellet in hot plasmas was investigated in the Large Helical Device (LHD). The penetration depth of the injected pellets in the experiment was compared to a theoretical model employing ablation due to the heat flux of fast ions as well as thermal electrons. Shallower penetration than that predicted based on the model considering only electrons was observed in LHD plasmas in the presence of highly energetic (up to 180 keV) fast ions due to neutral beam injection (NBI). This discrepancy can be quantified by the contribution of fast ions in terms of the stored energy of fast ions. The ablation model calculation taking into consideration the effect of thermal electrons and fast ions agrees with the experimental results obtained by LHD. Scaling which includes the fast-ion effect on penetration depth in LHD was compared with the wider multi-experiment database (IPADBASE) [L.R. Baylor et al., Nucl. Fusion 37, 445 (1997)].
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  • Masanori NUNAMI, Ryutaro KANNO, Shinsuke SATAKE, Hisanori TAKAMARU, Ta ...
    Type: Regular Articles
    2006 Volume 1 Pages 038
    Published: 2006
    Released: September 01, 2006
    JOURNALS FREE ACCESS
    In recent Large Helical Device (LHD) experiments, radial profiles of ion temperature, electric field, etc. have been measured in the m/n = 1/1 magnetic island produced by island control coils, where m is the poloidal mode number and n the toroidal mode number. When the plasma transport in radial profiles is numerically analyzed, an average over a magnetic flux-surface in the island is a very useful concept to understand the transport. When averaging, a proper labeling of the flux-surfaces is necessary. In general, it is not easy to label the flux-surfaces in a magnetic field containing the island, compared with the case of a magnetic field configuration having nested flux-surfaces. In the present paper, we have developed a new computational technique to label the magnetic flux-surfaces. This technique uses an optimization algorithm called the simulated annealing method. The flux-surfaces are discerned by using two labels: one is classification of the magnetic field structure, i.e., core, island, ergodic, and outside regions, and the other depends on the value of the toroidal magnetic flux. We have applied this technique to an LHD configuration with the m/n = 1/1 island, and successfully discriminated of the magnetic field structure.
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