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Kenji IMADERA, Yasuaki KISHIMOTO
原稿種別: Rapid Communications
2011 年 6 巻 p.
1201004
発行日: 2011/02/08
公開日: 2011/05/20
ジャーナル
フリー
The non-canonical Lie perturbation method for analyzing relativistic electron beams in free electron lasers [Y. Kishimoto et al., Phys. Plasmas 2, 1316 (1995)] is extended to the case with harmonic gyro-resonance due to the coexistence of a focusing wiggler and an axial guiding field, which allow the maximum beam current to be increased. By using non-canonical guiding-center variables, we have solved the particle motion not only far from the harmonic gyro-resonance but also near the resonance. Far from the resonance, the maximum beam current is found to increase in proportion to (B
g/B
w)
2 (B
w and B
g are the strength of the wiggler and guiding fields, respectively). On the other hand, near the resonance, the beam is found to be confined in a finite radial region and then transmitted because of higher order secular perturbations.
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Shuichi TAKAMURA, Takanori MIYAMOTO
原稿種別: Rapid Communications
2011 年 6 巻 p.
1202005
発行日: 2011/02/08
公開日: 2011/05/20
ジャーナル
フリー
One of the serious concerns for tungsten materials in fusion devices is the radiation defects caused by helium plasma irradiation, while the helium is one of fusion products. Fiber-formed nanostructure is worried to have a possible weakness against the plasma heat flux and may destroy the reflectivity as an optical mirror. In this communication an interesting method for a recovery of such a tungsten surface is shown.
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Suguru MASUZAKI, Masahiro KOBAYASHI, Mamoru SHOJI, Masayuki TOKITANI, ...
原稿種別: Rapid Communications
2011 年 6 巻 p.
1202007
発行日: 2011/02/08
公開日: 2011/05/20
ジャーナル
フリー
The helical divertor in the Large Helical Device (LHD) was partially modified before the experimental campaign in 2010 to demonstrate the ability of particle control by installing a baffle structure. The baffle structure consists of water cooled divertor plates combined with baffle plates and a dome in the private region. The neutral pressures in the modified and an existing unmodified helical divertors have been measured by using fast ion gauges during the campaign. The recycled neutral gas was successfully compressed in the modified divertor during discharges, and more than ten times higher pressure was observed there than in the unmodified divertor as expected from the neutral transport calculations.
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Mineyuki NISHIO, Hiroshi SAKUMA, Keiichi TAKASUGI
原稿種別: Rapid Communications
2011 年 6 巻 p.
1201009
発行日: 2011/02/28
公開日: 2011/05/20
ジャーナル
フリー
Ions accelerated in z-pinch experiments with either positive or negative discharge were measured by using a Thomson Parabola analyzer in order to understand the directional tendencies of the ion acceleration. Ions having energy on the order of MeV were observed in both positive and negative discharges. The velocity and energy of each ion species were measured to be considerably similar in magnitude, in spite of the difference in the polarity of the power supplies. The highest-velocity ions with different charges in each measurement lay on the constant velocity line. The model independent of the current direction should be considered as the main mechanism of ion acceleration in this study.
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Tatsuya UMAKOSHI, Hiroyasu ISHIDA, Toshiro KANEKO, Rikizo HATAKEYAMA
原稿種別: Rapid Communications
2011 年 6 巻 p.
1206015
発行日: 2011/03/18
公開日: 2011/06/10
ジャーナル
フリー
Nickel ions generated by sputtering with argon plasma are irradiated to fullerene C
60, and the possibility of synthesizing nickel atom endohedral fullerene is demonstrated. The mass spectra of the samples analyzed by laser desorption/ionization mass spectrometry are similar to a calculated isotope distribution ratio of the nickel atom endohedral fullerene. The optimum ion irradiation energy is approximately 35 eV, which corresponds to the energy expected by the molecular dynamics simulations.
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Seikichi MATSUOKA, Shinsuke SATAKE, Masayuki YOKOYAMA, Arimitsu WAKASA
原稿種別: Rapid Communications
2011 年 6 巻 p.
1203016
発行日: 2011/04/15
公開日: 2011/06/10
ジャーナル
フリー
Electron neoclassical transport is calculated taking non-local electron radial drift into account by using FORTEC-3D code which is based on δ f Monte Carlo method with time evolution of radial electric field, E
r. This simulation is implemented as the first global analysis for high-electron-temperature discharges in LHD. The simulation result of E
r is compared with the experimental observation and previous calculation results.
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Koichiro ADACHI, Mitsuo NAKAJIMA, Tohru KAWAMURA, Kazuhiko HORIOKA
原稿種別: Rapid Communications
2011 年 6 巻 p.
1201019
発行日: 2011/05/10
公開日: 2011/06/10
ジャーナル
フリー
We propose a new type of plasma source using a pinch discharge in a tapered capillary, which generates a dense moving plasma by electromagnetic compression and acceleration. The axial velocity and flux of the moving plasma are controllable and can be maximized by adjusting the taper angle. The behavior can be illustrated with a simple model considering the pinching dynamics of the current sheet.
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Takashi KIKUCHI, Hiroshi MORIWAKI, Hiromitsu NAKANISHI, Hironobu KONDO ...
原稿種別: Rapid Communications
2011 年 6 巻 p.
1206021
発行日: 2011/05/27
公開日: 2011/06/10
ジャーナル
フリー
The reaction of congo red, a well-known toxic azo dye, occurred after irradiation by a pulsed intense relativistic electron beam (PIREB). An aquation of congo red was irradiated by PIREB (2 MeV, 0.36 kA, 140 ns). After PIREB irradiation, the solution was measured by electrospray ionization-mass spectrometry and liquid chromatography/mass spectrometry. It was found that congo red underwent a reaction (77% conversion after five shots of PIREB irradiation) and the hydroxylated compounds of the dye were observed as reaction products.
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Yoshiaki MIYATA, Masayuki YOSHIKAWA, Mizuki SAKAMOTO, Masanori MIZUGUC ...
原稿種別: Rapid Communications
2011 年 6 巻 p.
1202090
発行日: 2011/06/24
公開日: 2011/08/12
ジャーナル
フリー
The physical mechanisms of the improvement of plasma confinement due to the formation of electrostatic potential and electric field were studied. A 12-keV gold neutral beam probe (GNBP) with the same capabilities as a heavy ion beam probe was operated on the GAMMA 10 tandem mirror. The simultaneous multipoint system was developed to measure the local electric field. The structure of the novel analyzer and the technique for measuring the local electric field were studied by using the calculation code of three-dimensional beam trajectory. It was possible for the first time to measure the local electric field in a single plasma shot by the simultaneous multipoint plasma potential measurement system using the GNBP in the GAMMA 10 tandem mirror.
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Masayuki YOSHIKAWA, Fumiaki YAGUCHI, Yoshiaki MIYATA, Masato MORIMOTO, ...
原稿種別: Rapid Communications
2011 年 6 巻 p.
1202095
発行日: 2011/07/12
公開日: 2011/08/12
ジャーナル
フリー
A yttrium-aluminum-garnet Thomson scattering (TS) system was constructed and applied to the tandem mirror GAMMA 10 plasma to measure the electron temperature. A large solid-angle TS light-collection system was set using a spherical mirror system and a large numerical aperture of bundled optical fiber. A five-channel polychromator with avalanche silicon photo diodes was employed after being calibrated with standard light. Calibration was performed by Rayleigh and Raman scattering. An electron temperature increase from 40 eV to 80 eV was observed with application of electron cyclotron heating to plug/barrier cells.
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Akihiro KUWAHATA, Hiroshi TANABE, Shingo ITO, Michiaki INOMOTO, Yasush ...
原稿種別: Rapid Communications
2011 年 6 巻 p.
1201127
発行日: 2011/08/20
公開日: 2011/10/13
ジャーナル
フリー
Large amplitude magnetic fluctuation with ion cyclotron range frequency was observed inside the current sheet region during magnetic reconnection in the plasma merging experiment for the first time. The fluctuation exhibited parallel phase velocity close to the drift velocity in the current sheet and parallel wavelength comparable with the ion gyroradius, suggesting that the reconnection rate enhancement is influenced by the drift kink instability of the current sheet.
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Takenori G WATANABE, Yasushi ONO, Takuma YAMADA, Shuji KAMIO, Qinghong ...
原稿種別: Rapid Communications
2011 年 6 巻 p.
1202131
発行日: 2011/09/12
公開日: 2011/10/13
ジャーナル
フリー
A close relationship between magnetic helicity injection and magnetic reconnection was observed during double-null formation of spherical tokamak (ST) plasmas. The magnetic reconnection of common flux into private flux causes concentration of current density along the current sheet, forming a high eigen-value area between the helicity source (coil flux) and the ST plasma. The formation of a plasmoid and its translation to core plasma indicate intermittent translation of the high eigen-value area, suggesting a mechanism for helicity injection.
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Junichi HIRATSUKA, Akira EJIRI, Makoto HASEGAWA, Yoshihiko NAGASHIMA, ...
原稿種別: Rapid Communications
2011 年 6 巻 p.
1202133
発行日: 2011/09/16
公開日: 2011/10/13
ジャーナル
フリー
A double-pass Thomson scattering system, in which a laser pulse makes a round trip through the plasma, was constructed. Using the same optics and a fast detection unit, we can resolve backward and forward scattering pulses in the signal. Because these scatterings reflect velocity distribution along different directions, electron temperature anisotropy can be estimated from the double-pass Thomson scattering system.
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Atsushi OKAMOTO, Hiroyuki TAKAHASHI, Sumio KITAJIMA, Mamiko SASAO
原稿種別: Rapid Communications
2011 年 6 巻 p.
1201153
発行日: 2011/12/28
公開日: 2012/01/16
ジャーナル
フリー
Time responses of a helium plasma to helium gas puffing without and with helium beam injection in a linear plasma device are experimentally investigated. Increase in the neutral density due to gas puffing is suppressed by ion beam injection. The experimental results show that a momentum transport from the ion beam to the puffed neutral particles occurs due to the charge exchange interaction, suggesting that charge exchange momentum transport is one of the processes responsible for the spatial redistribution of neutral atoms in partially ionized plasmas.
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Jun KIKUCHI, Takaaki MUTO, Shinji IBUKA, Shozo ISHII
原稿種別: Rapid Communications
2011 年 6 巻 p.
1201154
発行日: 2011/12/28
公開日: 2012/01/16
ジャーナル
フリー
We discuss the reduction of the amplitude of repetitive pulsed voltages to generate atmospheric-pressure microdischarges with a liquid cathode. The pulsed voltage was applied to a low-current DC glow discharge in a nozzle-to-liquid electrodes system. The pulsed microdischarges were operated at a voltage of less than 2.2 kV. The delay time of breakdown for the pulsed microdischarges increased with repetition frequency. At high repetitive operation, the liquid surface under the nozzle electrode deformed.
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Masanori NUNAMI, Tomo-Hiko WATANABE, Hideo SUGAMA, Kenji TANAKA
原稿種別: Regular Articles
2011 年 6 巻 p.
1403001
発行日: 2011/02/08
公開日: 2011/05/20
ジャーナル
フリー
Ion temperature (T
i) gradient modes (ITG modes) and zonal flows for high T
i discharges in the Large Helical Device (LHD) are investigated by linear gyrokinetic Vlasov simulation. In recent LHD experiments, high T
i plasmas are generated by neutral beam injection, and spatial profiles of density fluctuations are measured by phase contrast imaging (PCI) [K. Tanaka et al., Plasma Fusion Res. 5, S2053 (2010)]. The observed fluctuations most likely propagate in the direction of the ion diamagnetic rotation in the plasma frame, and their amplitudes increase with the growth of the temperature gradient. The results show the characteristics of ITG turbulence. To investigate the ITG modes and zonal flows in the experiment, linear gyrokinetic simulations were performed in the corresponding equilibria with different T
i profiles by using the GKV-X code [M. Nunami et al., Plasma Fusion Res. 5, 016 (2010)]. The simulation results predict unstable regions for the ITG modes in radial, wavenumber, and phase velocity spaces, in agreement with the PCI measurements. Thus, the fluctuations observed in the experiment are attributed to ITG instability. The responses of the zonal flows show clear contrasts in different field spectra that depend on the T
i profile and the radial position. In addition to the dependence on the field spectra, the zonal flow residual levels are enhanced by increasing the radial wavenumber as theoretically predicted.
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Naohiro KASUYA, Seiya NISHIMURA, Masatoshi YAGI, Kimitaka ITOH, Sanae- ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1403002
発行日: 2011/02/08
公開日: 2011/05/20
ジャーナル
フリー
Development of experimental diagnostics in fusion plasmas has made possible to measure plasma fluctuations with high spatial and temporal resolution. To detect a global mode, which contributes to global transport phenomena, it is helpful to use simulation data as a test field for the measurements. The turbulence diagnostic simulator is an assembly of codes for turbulence simulations and numerical diagnostics. Using the turbulence diagnostic simulator, a time series of turbulence data is obtained, on which numerical diagnostics are carried out to demonstrate how global modes to be observed. There exist modes, which are broad in the radial direction, and correlation analyses reveal the characteristic structures with a finite number of local observations in the radial direction, as in experiments.
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Osamu MITARAI, Kazuo NAKAMURA, Saya TASHIMA, Makoto HASEGAWA, Hiroshi ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1402003
発行日: 2011/02/08
公開日: 2011/05/20
ジャーナル
フリー
Ohmic plasma currents of up to 17 kA with a discharge duration of 0.32 s have been obtained in the Kyushu University Experiment with Steady-State Spherical Tokamak (QUEST) with the help of electron cyclotron wave (ECW) and cancellation coils (CCs). The CCs, originally installed to create a field null in the plasma breakdown phase, are essential for producing plasma current in QUEST. Although the ohmic coil current is initially biased and then reduced completely to zero to induce the plasma current in 15-20 ms, we demonstrate that the flat top of the plasma current exceeding 20 ms is maintained by the vertical field after the ohmic current is switched off. This type of operation is quite favorable for extending pulsed operation to the steady state by electron Bernstein wave current drive (EBCD).
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Mitsuru HONDA, Atsushi FUKUYAMA, Noriyoshi NAKAJIMA
原稿種別: Regular Articles
2011 年 6 巻 p.
1403008
発行日: 2011/02/28
公開日: 2011/05/20
ジャーナル
フリー
A neoclassical transport model compatible with a system of two-fluid equations is proposed, with an emphasis on the heat flux contribution. The model is based on the moment approach and is capable of accurately reproducing important neoclassical properties through a simple expression of the neoclassical viscosity tensor, with the aid of the NCLASS module. Applying neoclassical transport theory in a fluid context, we confirm the reproducibility of first-order flows, poloidal flows, neoclassical resistivity, bootstrap current and particle flux.
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Keiji SAWADA, Motoshi GOTO, Naomichi EZUMI
原稿種別: Regular Articles
2011 年 6 巻 p.
1401010
発行日: 2011/02/28
公開日: 2011/05/20
ジャーナル
フリー
The electron temperature and density, atomic hydrogen density and temperature in a helium-hydrogen RF plasma are determined from the visible emission line intensities of both atoms by considering photoexcitation from the ground state accompanied by radiation trapping in the plasma. From the observed helium line intensity, and the hydrogen Balmer γ line intensity which is little affected by photoexcitation, parameters other than the atomic hydrogen temperature are determined using a helium atom collisional-radiative model [Sawada et al., Plasma Fusion Res. 5, 001 (2010)], which includes photoexcitation for helium singlet P states, and a hydrogen atom collisional-radiative model in which photoexcitation is ignored. The atomic hydrogen temperature is determined to reproduce the Balmer α and β line intensities by using an iterative hydrogen atom collisional-radiative model [Sawada, J. Plasma Phys. 72, 1025 (2006)] that calculates the photoexcitation rates.
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Jacobo VARELA, Kiyomasa Y. WATANABE, Noriyoshi NAKAJIMA, Satoshi OHDAC ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1403013
発行日: 2011/04/15
公開日: 2011/05/20
ジャーナル
フリー
The aim of this 3D ballooning mode growth rates study is to point out the existence of ballooning activity in outward LHD configurations near the edge, and to find out how these instabilities are triggered in equilibria that simulate plasmas of high density core operations with internal transport barrier. 3D ballooning mode growth rates and Mercier stability were studied for several magnetic configurations with different beta values, and the research reveals an intense activity in outward configurations near the plasma edge, where Mercier criterion predicts stability for interchange modes and experimental data situates the density collapse events [S. Ohdachi et al., Contrib. Plasma Phys. 50, 552 (2010)].
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Naoyuki OYAMA, Hidenobu TAKENAGA, Takahiro SUZUKI, Yoshiteru SAKAMOTO, ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1402014
発行日: 2011/03/18
公開日: 2011/06/10
ジャーナル
フリー
In JT-60U, a frequency hopping reflectometer has been developed to evaluate the poloidal rotation velocity as a Doppler reflectometer and the radial correlation of density fluctuations in plasmas. The system can measure the radial profile of density fluctuations or the radial correlation profile at two spatial points within 250 ms by combining with the other fixed frequency reflectometer. The radial profiles of the poloidal rotation velocity evaluated from the Doppler-shifted frequency spectrum of density fluctuations show a positive radial electric field in co-rotating plasmas and a negative radial electric field in counter-rotating plasmas. Density fluctuation measurement at the internal transport barrier (ITB) using a correlation reflectometer revealed that long-range correlation increased when ITB was degraded owing to the central heating by electron cyclotron waves.
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Shigeru INAGAKI, Tokihiko TOKUZAWA, Kimitaka ITOH, Katsumi IDA, Sanae- ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1402017
発行日: 2011/04/15
公開日: 2011/06/10
ジャーナル
フリー
We report a detailed correlation technique to identify the long-range temperature fluctuation in the Large Helical Device. Correlation hunting has successfully realized the observation of electron temperature fluctuations, which are characterized by their correlation length comparable to the plasma minor radius, with low frequency of ∼ 1-3 kHz, ballistic radial propagation (at a speed of ∼1 km/s, of the order of diamagnetic drift velocity), spatial mode number of m/n = 1/1 (or 2/1), and amplitude of ∼2% at the maximum. Bicoherence analysis confirmed their nonlinear coupling with local microscopic turbulent fluctuations. This long-range temperature fluctuation is a possible carrier of fast propagation in transport processes observed so far. We also comment on the theoretical interpretation.
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Reza SHAKOURI, Babak SHOKRI
原稿種別: Regular Articles
2011 年 6 巻 p.
1401020
発行日: 2011/05/27
公開日: 2011/06/10
ジャーナル
フリー
The penetration of a magnetic field into a cylindrical plasma, in the time scale that is much longer than electron cyclotron period, is studied. A linear wave analysis is shown that the magnetic field penetrates rapidly into the plasma in radii smaller than the ion skin depth. Due to the axial symmetry, the problem reduces to a two-dimensional problem. The magnetic field evolution is numerically calculated. The ion density is also calculated. It is shown that during the penetration of the magnetic field, a gap appears between cathode and plasma. At the early times, at the plasma boundary, electrons move radially, and coupling of the electron velocity and the electric field induces the magnetic field. Electrons then gain a drift due to the field curvature that results in fast penetration of the magnetic field into the plasma.
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Tatsuya KOBAYASHI, Yoshihiko NAGASHIMA, Shigeru INAGAKI, Hiroyuki ARAK ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1401050
発行日: 2011/05/31
公開日: 2011/06/10
ジャーナル
フリー
A new method for estimating the wavenumber of a standing wave system by using three Langmuir probes is proposed. Analytical formulae are derived from a simple model in which two waves of the same frequency and the same wavenumber propagate in opposite directions. The proposed method can estimate the wavenumber correctly even if the two waves have equal amplitude.
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Ryuichi SAKAMOTO, Hiroshi YAMADA
原稿種別: Regular Articles
2011 年 6 巻 p.
1402085
発行日: 2011/06/24
公開日: 2011/08/12
ジャーナル
フリー
A three-dimensional observation of the solid hydrogen pellet ablation has been performed by using a fast stereo imaging camera to investigate the pellet ablation dynamics. The initial velocity component of the injected pellet is maintained during ablation in a hot plasma, and the pellet penetrates to the core plasma. On the other hand, it has been observed that part of high density pellet plasmoid, which is formed around the pellet substance by ablating hydrogen pellet, intermittently breaks away from the pellet ablating position and the breakaway plasmoid is transported across a confinement field. The breakaway plasmoid recurrently develops at the rate of about 100 times per millisecond and it is non-diffusively transported approximately 0.1 m during its several 10 µs lifetime in the opposite direction to the pellet motion, namely, toward the low magnetic field side. This observation gives a reasonable explanation for the difference between the pellet ablation position and the effective particle deposition profile.
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Kiyofumi MUKAI, Kazunobu NAGASAKI, Tohru MIZUUCHI, Vladimir ZHURAVLEV, ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1402111
発行日: 2011/07/27
公開日: 2011/08/12
ジャーナル
フリー
The electron density profile was measured using a microwave amplitude modulation (AM) reflectometer in Heliotron J plasmas, where plasma performance was improved using supersonic molecular beam injection (SMBI) as a fueling method. Immediately after the SMBI pulse, for the case in which the supersonic molecular beam penetrates deeply, the density profile rapidly peaks, and the electron density increases in both core and edge regions. Afterward, while the line-averaged electron density is monotonically increasing, the density profile becomes more peaked. In this phase, the edge electron density measured by a Langmuir probe decreases and the peaking factor of the SX profiles measured by an absolute extreme ultraviolet array increases. These trends are consistent with the electron density trend determined by the AM reflectometer. SMBI affects particle confinement and transport, thus possibly increasing plasma stored energy.
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Akiyoshi MURAKAMI, Junichi MIYAZAWA, Koji YASUI, Takanori MURASE, Naok ...
原稿種別: Regular Articles
2011 年 6 巻 p.
1402135
発行日: 2011/10/21
公開日: 2011/12/01
ジャーナル
フリー
Non-local transport and electron temperature fluctuations triggered by supersonic gas puffing (SSGP) in high-temperature helical plasmas in the Large Helical Device (LHD) are reported. After a short-pulse SSGP, the core electron temperature increased while the edge electron temperature decreased. SSGP triggered a longer core temperature increase than that triggered by a small impurity pellet injection. The temperature profile, which was relatively flat inside the half minor radius before SSGP, became parabolic after non-local transport was triggered. Fluctuations were excited in the electron temperature signals around the half minor radius. The frequency of these fluctuations increased from ∼ 400 Hz to ∼ 1 kHz within ∼ 0.1 s and the amplitude decreased correspondingly. The temperature fluctuations inside and outside of the half minor radius had opposite phases. Magnetic fluctuations resonating near the half minor radius were observed simultaneously with the electron temperature fluctuations.
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Takuya NAGASAKA, Masatoshi KONDO, Akio SAGARA, Takeo MUROGA
原稿種別: Regular Articles
2011 年 6 巻 p.
1405146
発行日: 2011/12/02
公開日: 2011/12/26
ジャーナル
フリー
Corrosion characteristics of hydrogen-permeation materials (e.g., Pd-Ag, pure V, Nb, and Ta) are examined in molten salt Flinak, in order to develop a hydrogen-recovery section for a Flinak forced convection loop “Operational Recovery of Separated Hydrogen and Heat Inquiry -1 (Orosh
2 i-1).” It is determined that their corrosion rate is not significant at 873 K under static conditions, compared with that of JLF-1 ferritic steel. However, pure V indicates a relatively high weight gain, likely due to O absorption. Dissolution of highly radioactive elements (e.g., Ag and Nb) is also indicated. The corrosion mechanisms and characteristics of the constituent elements are analyzed.
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Naoaki MIYATO, Bruce D. SCOTT
原稿種別: Regular Articles
2011 年 6 巻 p.
1403147
発行日: 2011/12/02
公開日: 2011/12/26
ジャーナル
フリー
Representation of particle fluid moments in terms of fluid moments in the modified guiding-centre model for flowing plasmas with large E × B velocity [N. Miyato et al., J. Phys. Soc. Jpn. 78, 104501 (2009)] is derived from the formal exact representation by a perturbative expansion in the subsonic flow case. It is similar to that in the standard gyrokinetic model in the long wavelength limit, except it has an additional flow term. The flow term has no effect on the representation for particle density, leading to the same representation as the standard one formally. In the conventional guiding-centre models for flowing plasmas, on the other hand, the representation for particle density is different from the standard one. This is due to the difference in the transformation for the guiding-centre position. Although the exact representation usually used in the standard gyrokinetic model has a different form from that in the modified guiding-centre case, correspondence between the two models is shown by considering the alternative form of exact representation in the standard gyrokinetic case. The representation for particle density is also obtained from the single particle Lagrangian by a variational method which is used to derive the representation in the transonic case.
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Akihiro SUGAHARA, Yasuaki KISHIMOTO
原稿種別: Regular Articles
2011 年 6 巻 p.
2401022
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
In recent years, there has been a growing awareness that large scale simulation plays an important role in various science fields. To assist such simulation studies in which many collaborators working at geographically different places participate, we developed a unique remote collaboration system, referred to as SIMON (SImulation MONitoring) [A. Sugahara and Y. Kishimoto: J. Plasma Fusion Res. 84, 51 (2008)]. This system is based on the client-server model, where the simulation (client) running on a supercomputer controls an external workstation (server) by sending various requests such as data transfer, analysis, visualization, updating website, etc. via network. Here, in order to increase the reliability of the network connection, we apply a method which establishes the login-shell of SSH automatically, and that ciphers the password by utilizing plural encodes. Furthermore, in order to provide an efficient environment for data analyses on the website, we introduced a method that stratifies the capability of visualization. By applying the system to a specific simulation project of laser-matter interaction, we confirmed that the system works well as a collaboration platform on which many collaborators work with each other.
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Takashi IWATA, Seiichi TAKAHASHI, Yukiharu OHSAWA
原稿種別: Regular Articles
2011 年 6 巻 p.
2401025
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
Ultrarelativistic positron acceleration along the magnetic field due to shock waves in an electron-positron-ion plasma is studied with use of one-dimension (one space coordinate and three velocities), fully kinetic, fully electromagnetic, particle simulations. First, ultrarelativistic acceleration to γ ∼ 10
4 in a uniform external magnetic field B
0 is demonstrated with a simulation with the shock speed v
sh close to c cos θ, where c is the speed of light and θ is the angle between the external magnetic field and the wave normal. Then, the effect of non-uniformity of B
0 is investigated; comparisons are made of two different cases: 1) the strength of the external magnetic field increases as a shock wave propagates (∇B
0 is parallel to the wave normal), and 2) it decreases (∇B
0 is unti-parallel to the wave normal). It is found that positron acceleration in the latter tends to be stronger than in the former.
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Yuichi KONDO, Mieko TOIDA
原稿種別: Regular Articles
2011 年 6 巻 p.
2401026
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
The effects of ion composition on oblique magnetosonic waves in a two-ion-species plasma are studied theoretically and numerically. First, it is analytically shown that the KdV equation for the low-frequency mode, the lower branch of magnetosonic waves, is valid for amplitudes ε < ε
(l−)max, where ε
(l−)max is a measure of the upper limit of the amplitude of the rarefactive solitary pulse of the low-frequency mode and is given as a function of the propagation angle of the wave θ, the density ratio and cyclotron frequency ratio of two ion species. The value of ε
(l−)max increases with decreasing θ. Next, with electromagnetic particle simulations, the nonlinear evolution of the low- and high-frequency modes is examined. It is demonstrated that shorter-wavelength low- and high-frequency-mode waves are generated from a long-wavelength low-frequency-mode pulse if its amplitude ε exceeds ε
(l−)max.
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Shinya MAEYAMA, Akihiro ISHIZAWA, Tomo-Hiko WATANABE, Noriyoshi NAKAJI ...
原稿種別: Regular Articles
2011 年 6 巻 p.
2401028
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
A semi-Lagrangian scheme is applied for the first time to computations of charged particle motions along magnetic field lines, to numerically solve the δf gyrokinetic equations in a flux tube geometry. This new solver adopted in the gyrokinetic Vlasov simulations has an advantage over the conventional Eulerian codes in calculating the parallel dynamics, because semi-Lagrangian schemes are free of the Courant-Friedrichs-Lewy (CFL) condition that restricts the time step size. A study of the accuracy of the parallel motion simulations reveals that numerical errors mainly stem from spatial (not temporal) discretization for realistic values of the grid spacing and time step, and it demonstrates the advantage of the semi-Lagrangian scheme. This novel numerical method is successfully applied to linear gyrokinetic simulations of the ion temperature gradient instability, where time steps larger than those restricted by the CFL condition can be employed.
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Mamoru SHOJI, Suguru MASUZAKI, Tomohiro MORISAKI, Ryuichi SAKAMOTO, Ma ...
原稿種別: Regular Articles
2011 年 6 巻 p.
2401035
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
A promising candidate of a vacuum pumping system for the closed helical divertor in the large helical device is proposed using a three-dimensional neutral particle transport simulation code (EIRENE) and a finite element based multi-physics analysis software (ANSYS). It shows that heat load on a gas/liquid He cooled panel by thermal conduction due to high energy neutral hydrogen atoms is dominant over that by radiation from divertor plates heated by the LHD peripheral plasma. It proves that optimization of the configuration of the vacuum pumping system can significantly reduce the heat load on the panel without serious degradation of the pumping efficiency.
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Kazuo OGURA, Kiyoyuki YAMBE, Hiroyuki YOSHIMURA, Masatoh TAKAHASHI
原稿種別: Regular Articles
2011 年 6 巻 p.
2401039
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
Backward wave oscillation based on a cylindrical surface wave of Smith-Purcell free electron laser (SP-FEL) is demonstrated. The SP-FEL is composed of a metal cylinder having a periodically corrugated wall and a surrounding hollow straight waveguide. Corrugation parameters are those used in K-band backward wave oscillators (BWOs). The metal cylinder has a surface wave due to the corrugation. The cylindrical surface wave is excited by an axially injected coaxial annular beam. Radiations due to the backward wave oscillation based on the cylindrical surface wave are examined in a weakly relativistic region less than 100 kV. An oscillation starting voltage exists for the backward wave oscillation as in the case of hollow oversized BWO. The frequencies are in K-band and are determined by the cylindrical corrugation. Radiations up to tens of kW are obtained.
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Susumu FUJIWARA, Takashi ITOH, Masato HASHIMOTO, Yuichi TAMURA, Hiroak ...
原稿種別: Regular Articles
2011 年 6 巻 p.
2401040
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
Micellar shape change in an amphiphilic solution is investigated by a molecular dynamics simulation of coarse-grained semiflexible amphiphilic molecules with explicit solvent molecules. Our simulations show that a cylindrical micelle is obtained at small molecular rigidity while a disc-shaped micelle appears at large molecular rigidity. We find that most chains are in an extended conformation at large molecular rigidity whereas the fraction of the chains in a bent conformation becomes large at small molecular rigidity. It is also ascertained that the micellar shape starts to change immediately after sudden increase of the molecular rigidity while an induction time is needed to change the micellar shape after sudden decrease of the molecular rigidity. This result can be qualitatively explained by considering the bond-bending potential energy and the conformational entropy of the amphiphilic molecules.
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Tetsutarou OISHI, Kozo YAMAZAKI, Yoshihito HORI, Hideki ARIMOTO
原稿種別: Regular Articles
2011 年 6 巻 p.
2401052
発行日: 2011/07/12
公開日: 2012/01/23
ジャーナル
フリー
To sustain deuterium (D) - tritium (T) burning plasmas efficiently and to reduce T fuel injection into magnetic confinement fusion reactors, the amount and the ratio of D and T both in the bulk plasmas and in the fueling systems should be controlled accurately. In order to analyze the relationship among fueling methods, the D/T fuel ratio, and reactor output power numerically, we applied the toroidal transport analysis linkage (TOTAL) equilibrium-transport integrated simulation code to model the fuel supply in D-T burning plasmas. It was revealed that operation with a lower tritium ratio in the fuel pellet and a higher electron density can reduce the T fuel injection. The isotope effect of the ion mass on the confinement property was also investigated. As a preliminary result, a concern emerged that the improved confinement of helium ions causes an unintended increase of the electron density, if the particle diffusion coefficient of the ions has a negative correlation with the ion mass.
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Shun-ichi OIKAWA, Takahiro SHIMAZAKI, Emi OKUBO
原稿種別: Regular Articles
2011 年 6 巻 p.
2401058
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
We have solved the two-dimensional time-dependent Schrödinger equation for a single particle in the presence of a nonuniform magnetic field for initial speeds of 10-100 m/s. By linear extrapolation, it is shown that the variance, or the uncertainty, in position would reach the square of the interparticle separation n
−2/3 with a number density of n = 10
20 m
−3 in a time interval of the order of 10
−4 sec. After this time the wavefunctions of neighboring particles would overlap, as a result the conventional classical analysis may lose its validity: Plasmas may behave more-or-less like extremely-low-density liquids, not gases, since the size of each particle is of the same order of the interparticle separation.
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Teruou TAKAYAMA, Atsushi KAMITANI, Taku ITOH, Hiroaki NAKAMURA
原稿種別: Regular Articles
2011 年 6 巻 p.
2401059
発行日: 2011/07/01
公開日: 2012/01/23
ジャーナル
フリー
Possibility of the accuracy improvement in the permanent magnet method for measuring the critical current density of a high-temperature superconducting (HTS) thin film has been investigated numerically. To this end, a numerical code has been developed for analyzing the shielding current density in an HTS sample. By using the code, the permanent magnet method has been reproduced numerically. The results of computations show that, by using the magnet strength B
F as large as possible, the high accuracy can be assured with little effort. Furthermore, in order to improve the measurement accuracy of the critical current density near the film edge, it is necessary to use the magnet with the smallest radius.
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