Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
Volume 6
Showing 1-50 articles out of 155 articles from the selected issue
Review Articles
  • Rikizo HATAKEYAMA, Toshiro KANEKO
    Type: Review Articles
    2011 Volume 6 Pages 1106011
    Published: March 04, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    Recent years have brought about a rapid rise in research on applications in biological and medical fields including cell and tissue inactivation, sterilization and disinfection, blood coagulation, therapy, surgery, pharmaceuticals, biosensing, and biochips by exploiting low-pressure, atmospheric-pressure, and solution plasma processes. Many of the basic constituent materials of biological organisms are nanometer-scale in size, thus presenting the possibility of a growing field of science and technology focused on a fusion between “bio” and “nano” mechanisms; we are now in the germinal stage of a new era of next-generation applied research in the biological and medical applications of nanocarbons typified by fullerenes and carbon nanotubes. In this context, the authors have proposed and implemented research utilizing nanoscopic processes in advanced gas, liquid, and gas-liquid interfacial plasmas, directed toward the creation of synthetic materials and devices composed of nanocarbons, nanoparticles, and biomolecules. This research is positioned to advance the establishment of nano-bio fusion science opened and created with plasmas to construct next-generation nanobio and medical systems relating to nanobio-electronics devices, intracellular nanoengineering, and nanomedicine.
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  • Ramon J. LEEPER, The National Ignition Campaign Team
    Type: Review Articles
    2011 Volume 6 Pages 1104012
    Published: March 04, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    This paper will review the ignition fusion research program that is currently being carried out on the National Ignition Facility (NIF) located at Lawrence Livermore National Laboratory. This work is being conducted under the auspices of the National Ignition Campaign (NIC) that is a broad collaboration of national laboratories and universities that together have developed a detailed research plan whose goal is ignition in the laboratory. The paper will begin with a description of the NIF facility and associated experimental facilities. The paper will then focus on the ignition target and hohlraum designs that will be tested in the first ignition attempts on NIF. The next topic to be introduced will be a description of the diagnostic suite that has been developed for the initial ignition experiments on NIF. The paper will then describe the experimental results that were obtained in experiments conducted during the fall of 2009 on NIF. Finally, the paper will end with a description of the detailed experimental plans that have been developed for the first ignition campaign that will begin later this year.
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  • Ritoku HORIUCHI, NSRP members
    Type: Review Articles
    2011 Volume 6 Pages 2101055
    Published: July 12, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    Based on the past two-decades activities at the Theory and Computer Simulation Center (TCSC) and the Department of Simulation Science (DSS) in the National Institute for Fusion Science (NIFS), the Numerical Simulation Research Project (NSRP) has been launched to continue the activities in TCSC and DSS, and evolve them in a more systematic way for the re-organization of NIFS in 2010. In this study, the progress of simulation science at NIFS in the past two decades is reviewed and an overview of the NSRP for the foreseeable future is reported.
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  • Akio KOMORI, Satoru SAKAKIBARA, Akio SAGARA, Ritoku HORIUCHI, Hiroshi ...
    Type: Review Articles
    2011 Volume 6 Pages 2102149
    Published: December 02, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    The National Institute for Fusion Science (NIFS), which was established in 1989, promotes academic approaches toward the exploration of fusion science for steady-state helical reactor and realizes the establishment of a comprehensive understanding of toroidal plasmas as an inter-university research organization and a key center of worldwide fusion research. The Large Helical Device (LHD) Project, the Numerical Simulation Science Project, and the Fusion Engineering Project are organized for early realization of net current free fusion reactor, and their recent activities are described in this paper. The LHD has been producing high-performance plasmas comparable to those of large tokamaks, and several new findings with regard to plasma physics have been obtained. The numerical simulation science project contributes understanding and systemization of the physical mechanisms of plasma confinement in fusion plasmas and explores complexity science of a plasma for realization of the numerical test reactor. In the fusion engineering project, the design of the helical fusion reactor has progressed based on the development of superconducting coils, the blanket, fusion materials and tritium handling.
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  • William M. TANG
    Type: Review Articles
    2011 Volume 6 Pages 2103056
    Published: October 21, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    This paper highlights the scientific and computational challenges facing the Fusion Simulation Program (FSP) - a major national initiative in the United States with the primary objective being to enable scientific discovery of important new plasma phenomena with associated understanding that emerges only upon integration. This requires developing a predictive integrated simulation capability for magnetically-confined fusion plasmas that are properly validated against experiments in regimes relevant for producing practical fusion energy. It is expected to provide a suite of advanced modeling tools for reliably predicting fusion device behavior with comprehensive and targeted science-based simulations of nonlinearly-coupled phenomena in the core plasma, edge plasma, and wall region on time and space scales required for fusion energy production. As such, it will strive to embody the most current theoretical and experimental understanding of magnetic fusion plasmas and to provide a living framework for the simulation of such plasmas as the associated physics understanding continues to advance over the next several decades. Substantive progress on answering the outstanding scientific questions in the field will drive the FSP toward its ultimate goal of developing the ability to predict the behavior of plasma discharges in toroidal magnetic fusion devices with high physics fidelity on all relevant time and space scales. From a computational perspective, this will demand computing resources in the petascale range and beyond together with the associated multi-core algorithmic formulation needed to address burning plasma issues relevant to ITER - a multibillion dollar collaborative experiment involving seven international partners representing over half the world's population. Even more powerful exascale platforms will be needed to meet the future challenges of designing a demonstration fusion reactor (DEMO). Analogous to other major applied physics modeling projects (e.g., Climate Modeling), the FSP will need to develop software in close collaboration with computers scientists and applied mathematicians and validated against experimental data from tokamaks around the world. Specific examples of expected advances needed to enable such a comprehensive integrated modeling capability and possible “co-design” approaches will be discussed.
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  • Benjamin TOBIAS, Neville C. LUHMANN, Jr., Calvin W. DOMIER, Xiangyu K ...
    Type: Review Articles
    2011 Volume 6 Pages 2106042
    Published: August 11, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    Techniques for visualizing turbulent flow in nature and in the laboratory have evolved over half a millennium from Leonardo da Vinci's sketches of cascading waterfalls to the advanced imaging technologies which are now pervasive in our daily lives. Advancements in millimeter wave imaging have served to usher in a new era in plasma diagnostics, characterized by ever improving 2D, and even 3D, images of complex phenomena in tokamak and stellarator plasmas. Examples at the forefront of this revolution are electron cyclotron emission imaging (ECEI) and microwave imaging reflectometry (MIR). ECEI has proved to be a powerful tool as it has provided immediate physics results following successful diagnostic installations on TEXTOR, ASDEX-U, DIII-D, and KSTAR. Recent results from the MIR system on LHD are demonstrating that this technique has the potential for comparable impact in the diagnosis of electron density fluctuations. This has motivated a recent resurgence in MIR research and development, building on a prototype system demonstrated on TEXTOR, toward the realization of combined ECEI/MIR systems on DIII-D and KSTAR for simultaneous imaging of electron temperature and density fluctuations. The systems discussed raise the standard for fusion plasma diagnostics and present a powerful new capability for the validation of theoretical models and numerical simulations.
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Rapid Communications
Letters
  • Yoneyoshi KITAGAWA, Yoshitaka MORI, Ryohei HANAYAMA, Shinichiro OKIHAR ...
    Type: Letters
    2011 Volume 6 Pages 1306006
    Published: February 08, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    The first use of a high-repetition-rate laser-diode (LD)-pumped laser in a fusion target experiment is demonstrated. An LD-pumped Nd-solid state laser's output is coupled to a Ti:sapphire laser, enabling the resulting HAMA laser to generate 2-J, 815-nm-wavelength output with a pulse width of 150 fs and a repetition rate of 10 Hz. A photon-to-photon efficiency of 1.25% (electric-to-photonic 0.7%) is achieved, which is an order of magnitude higher than that of current flash-lamp lasers. Irradiation of a 500-µm-thick deuterated polystyrene film by a 0.6-J pulse yielded 105 DD fusion neutrons. The efficiency from the electric input to the neutron yield is 10 times higher than the flash-lamp-pumped table-top lasers.
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  • Hiroshi TOJO, Takaki HATAE, Kiyoshi ITAMI
    Type: Letters
    2011 Volume 6 Pages 1302018
    Published: May 10, 2011
    Released: June 10, 2011
    JOURNALS FREE ACCESS
    A new method of in-situ relative calibration for Thomson scattering diagnostics using a double-pass scattering system is proposed. The ratio of scattered light signals between the first and second pass depends on electron temperature (Te), making it possible to evaluate Te without considering relative transmissivities. The relative transmissivities of each spectral channel can be determined at the same time. The feasibility of the method based on parameters in a JT-60SA Thomson scattering diagnostic is also examined.
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  • Yoshihide SHIBATA, Kiyomasa WATANABE, Noriyasu OHNO, Masaaki OKAMOTO, ...
    Type: Letters
    2011 Volume 6 Pages 1302136
    Published: October 21, 2011
    Released: December 01, 2011
    JOURNALS FREE ACCESS
    In order to validate some current decay models during the current quench, the plasma current decay time was studied using the experimental plasma resistance and inductance in high poloidal beta, βp, disruptions in JT-60U. The plasma resistance and inductance were evaluated from an equilibrium calculation code and the measurement value of a magnetic sensor, the electron temperature evaluated by using ECE measurement and the electron density measured by FIR interferometer. In high βp disruptions, it was found that the electron temperature at the plasma center just after current quench starts was approximately 1-4 keV under almost the same current decay time observed during the initial phase of current quench. This result indicates that the electron temperature itself plays no major role in the determination of the current decay time in the initial phase of current quench. Moreover, the current decay time predicted by a modified L/R model [Y. Shibata et al., Nucl. Fusion 50, 025015 (2010)], in which the time derivative of plasma inductance was considered, was in good agreement with the experimental current decay time, while the values obtained from the conventional L/R model were two orders of magnitude larger than the experimental results.
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  • Ayumi ANDO, Hidetaka UNO, Toshifumi ASANO, Tsuneo URISU, Satoshi HAMAG ...
    Type: Letters
    2011 Volume 6 Pages 1306155
    Published: December 28, 2011
    Released: January 16, 2012
    JOURNALS FREE ACCESS
    It is shown that neuronal model cells PC12 (rat adrenal pheochromocytoma cell line) can be cultured on a silicon (Si) substrate with the use of extracellular matrix (ECM) patterned by atmospheric-pressure plasmas (APPs). Arrangement of neuron cells in a desired pattern on a Si chip is an important step for the development of neuron cell chips. In the experiments, 100-200 µm wide strips of ECM (Poly-L-Lysine) layers arranged in parallel were formed on a 1 cm2 area of a Si surface by the APP etching technique and PC12 cells were shown to grow on the ECM strips. The APP etching technique for ECM layers provides a simple mean of arranging neuron cells on a relatively large area of a Si surface.
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Regular Articles
  • Masanori NUNAMI, Tomo-Hiko WATANABE, Hideo SUGAMA, Kenji TANAKA
    Type: Regular Articles
    2011 Volume 6 Pages 1403001
    Published: February 08, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    Ion temperature (Ti) gradient modes (ITG modes) and zonal flows for high Ti discharges in the Large Helical Device (LHD) are investigated by linear gyrokinetic Vlasov simulation. In recent LHD experiments, high Ti 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 Ti 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 Ti 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- ...
    Type: Regular Articles
    2011 Volume 6 Pages 1403002
    Published: February 08, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    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 ...
    Type: Regular Articles
    2011 Volume 6 Pages 1402003
    Published: February 08, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 1403008
    Published: February 28, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 1401010
    Published: February 28, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    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 ...
    Type: Regular Articles
    2011 Volume 6 Pages 1403013
    Published: April 15, 2011
    Released: May 20, 2011
    JOURNALS FREE ACCESS
    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, ...
    Type: Regular Articles
    2011 Volume 6 Pages 1402014
    Published: March 18, 2011
    Released: June 10, 2011
    JOURNALS FREE ACCESS
    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- ...
    Type: Regular Articles
    2011 Volume 6 Pages 1402017
    Published: April 15, 2011
    Released: June 10, 2011
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 1401020
    Published: May 27, 2011
    Released: June 10, 2011
    JOURNALS FREE ACCESS
    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 ...
    Type: Regular Articles
    2011 Volume 6 Pages 1401050
    Published: May 31, 2011
    Released: June 10, 2011
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 1402085
    Published: June 24, 2011
    Released: August 12, 2011
    JOURNALS FREE ACCESS
    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, ...
    Type: Regular Articles
    2011 Volume 6 Pages 1402111
    Published: July 27, 2011
    Released: August 12, 2011
    JOURNALS FREE ACCESS
    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 ...
    Type: Regular Articles
    2011 Volume 6 Pages 1402135
    Published: October 21, 2011
    Released: December 01, 2011
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 1405146
    Published: December 02, 2011
    Released: December 26, 2011
    JOURNALS FREE ACCESS
    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 (Orosh2 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
    Type: Regular Articles
    2011 Volume 6 Pages 1403147
    Published: December 02, 2011
    Released: December 26, 2011
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 2401022
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 2401025
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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 ∼ 104 in a uniform external magnetic field B0 is demonstrated with a simulation with the shock speed vsh 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 B0 is investigated; comparisons are made of two different cases: 1) the strength of the external magnetic field increases as a shock wave propagates (∇B0 is parallel to the wave normal), and 2) it decreases (∇B0 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
    Type: Regular Articles
    2011 Volume 6 Pages 2401026
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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 ...
    Type: Regular Articles
    2011 Volume 6 Pages 2401028
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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 ...
    Type: Regular Articles
    2011 Volume 6 Pages 2401035
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 2401039
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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 ...
    Type: Regular Articles
    2011 Volume 6 Pages 2401040
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 2401052
    Published: July 12, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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
    Type: Regular Articles
    2011 Volume 6 Pages 2401058
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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 = 1020 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
    Type: Regular Articles
    2011 Volume 6 Pages 2401059
    Published: July 01, 2011
    Released: January 23, 2012
    JOURNALS FREE ACCESS
    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 BF 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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