Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
Volume 7
Showing 51-100 articles out of 159 articles from the selected issue
Regular Articles
  • Byron J. PETERSON, Masahiro KOBAYASHI, Ryuichi SANO, Shwetang N. PAND ...
    2012 Volume 7 Pages 2402041
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    InfraRed imaging Video Bolometers (IRVBs) can provide hundreds of channels of bolometric data forming an image of the plasma radiation [B.J. Peterson, Rev. Sci. Instrum. 71, 3696 (2000)]. By calculating the geometry matrix (or responsematrix) of the detector field of view (FoV) with respect to a predefined three dimensional (3D) plasma grid of plasma voxels these geometry matrices can be used for 3D tomography of the plasma radiation. This is done by assuming that the plasma reproduces itself every half field period. Then by combining the FOV of 3 IRVBs with different views of the plasma (top, tangential, semi-tangential), one large geometry matrix can be derived relating 1968 IRVB channels to 13,161 plasma voxels. Results indicate that FoVs should be modified or supplemented to view plasma voxels near the helical divertor xpoints of the diagonal cross-sections (5< φ < 13) which are in the shadows of the helical coils.
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  • Todd E. EVANS, the DIII-D Team
    2012 Volume 7 Pages 2402046
    Published: May 10, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    Uncontrolled Type-I Edge Localize Modes (ELMs) are expected to cause melting of the tungsten divertors in ITER. Methods for controlling ELMs in ITER include pellet pacing and Resonant Magnetic Perturbation (RMP) fields produced by in-vessel, non-axisymmetric, coils. Type-I ELMs have been reproducibly suppressed and mitigated in DIII-D H-mode plasmas with a variety of shapes and pedestal collisionalities using RMP fields of order 10−3 BT. In these experiments the response of Type-I ELMs to applied RMP fields, with a principal toroidal mode number n = 3, varies dramatically. In some cases there is an evolution in the ELM dynamics involving combinations of small high frequency Dα spikes mixed with mitigated Type-I ELMs prior to reaching an ELM suppressed state. In other cases, there is continuous change in the frequency and amplitude of the Type-I ELMs. A reduced set of plasma parameters, that significantly affect the dynamics of the ELMs immediately following the application of the RMP field, have been identified. The dynamics of mitigated ELMs are generally consistent with those seen during Type-I through Type-V ELMs although several new types of ELM dynamics have also been observed in plasmas with relatively low toroidal fields as well as during q95 ramps.
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  • Akio SANPEI, Kensuke OKI, Daisuke FUKAHORI, Kazuaki DEGUCHI, Seiya NAK ...
    2012 Volume 7 Pages 2402052
    Published: June 07, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    A time-resolved vertical soft X-ray (SXR) imaging system was constructed. To identify the structure of the magnetic island using the obtained SXR images, we calculated the two-dimensional (2-D) image expected from low-aspect-ratio (low-A) reversed field pinch (RFP) plasmas. The 2-D image was found to reflect the change in the radiation power caused by the magnetic island. A preliminary experimental result in which we observed vertical SXR imagesfrom the quasi-periodicquasi-single helicity (QSH) state in low-A RFP plasmas is presented. We successfully obtained the time evolution of SXR images from the vertical port. By comparing the observed images with simulated images, we found that the evolution of the experimental SXR image suggests a rotating helical configuration.
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  • Hayato TSUCHIYA, Yuuki TAKEMURA, Yoshio NAGAYAMA, Daisuke KUWAHARA, Ki ...
    2012 Volume 7 Pages 2402056
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    This study reports characteristics of the interchange mode-like magnetohydrodynamic (MHD) mode through comparisons between fluctuations measured by electron cyclotron emission (ECE) and Soft X-ray (SX) in the Large Helical Device (LHD). The MHD mode, whose frequency is 0.74 to 2.7 kHz, is enhanced near ρ = 0.8, ι = 1. Te fluctuation data measured by ECE can identify the mode width by using the displacement amplitude profile whereas SX data cannot show the structure clearly. Furthermore the dependence of the width and amplitude on the pressure gradient is shown using Te fluctuations.
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  • Erhui WANG, Shigeru MORITA, Motoshi GOTO, Masahiro KOBAYASHI, Chun ...
    2012 Volume 7 Pages 2402059
    Published: June 07, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    Vertical profiles of edge impurity line emissions of He II and C IV have been measured at different toroidal locations of Large Helical Device (LHD) by scanning horizontally a space-resolved EUV spectrometer in order to observe the edge distribution at different poloidal locations. Radial location of He II with ionization energy of Ei = 54.4 eV reflects the penetration depth of neutral helium and radial location of C IV with Ei = 64.5 eV expresses the index of plasma edge boundaryin ergodic layer of LHD. The result indicates that the radial position of He II is located at inner side than that of C IV, whereas the ionization energy of He II is smaller than that of C IV. It is found that the radial position of He II estimated from the C IV position has a nearly constant distance of 4 mm from the plasma edge against different poloidal locations including region near X-points. The distance is in a good agreement with analysis assumed neutral helium influx with room temperature (300 K). It suggests that the neutral helium mainly enter the plasma as background gas in the vacuum vessel, but not as recycling particle.
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  • Leonid ELISEEV, Alexer MELNIKOV, Stanislav PERFILOV, Carlos HIDALGO
    2012 Volume 7 Pages 2402064
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    The paper proposes a method to measure poloidal rotation velocity of toroidal plasma vpol using Heavy Ion Beam Probe (HIBP) with a multi-slit energy analyzer. The method is based on calculation of phase shift between broadband density turbulence measured simultaneously in two sample volumes, located at the same magnetic surface but separated poloidally. Oscillatory component of HIBP beam current is used as a density turbulence characteristic. HIBP is capable to provide the temporal evolution of the vpol in a fixed radial position and also the vpol profile by periodic radial scan. Method was verified in real plasma experiment in ECRH and NBI discharges on the TJ-II stellarator. Result shows that in low density discharges (ne ≈ 0.3-0.5×1019 m−3) absolute values of local vpol is about 4-6 km/s, oriented in the ion diamagnetic drift direction. When HIBP operates for radial scans, it is conventionally measuring the plasma potential profile, and so provides the radial electric field Er and velocity of E × B drift (vE×B) at the same time as plasma rotation. Experimental data shows that in low density ECRH plasma the rotation velocity coincides with E × B velocity within achieved experimental accuracy. When the density is increasing, both vE×B and vpol tends to decrease and then change the sign at threshold plasma densities in the range of ne ≈ 0.7-1×1019 m−3. With this new proposed technique HIBP becomes the new effective tool to study plasma rotation and turbulence characteristics in toroidal plasmas.
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  • Junichi MIYAZAWA, Takuya GOTO, Ryuichi SAKAMOTO, Gen MOTOJIMA, Chihiro ...
    2012 Volume 7 Pages 2402072
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    The performance of high-density plasmas heated by neutral beam (NB) injection in a vertically elongated configuration using four poloidal coils has been investigated in LHD and shown to be better than that in the normal configuration using six poloidal coils. Reduction of poloidal coils is favorable in designing an LHD-type helical reactor FFHR-d1, from both points of view of cost reduction and realization of large maintenance ports. In the experiment, no clear difference between the two configurations was recognized in the relation between the central density and the central pressure. Meanwhile, a factor Cexp used in the direct profile extrapolation (DPE) method is smaller in the vertically elongated configuration, where Cexp is proportional to the reactor size, Rreactor, at a given reactor magnetic field, Breactor, i.e., Rreactor CexpBreactor−4/3. The difference in Cexp between the two configurations is enhanced to > 10% as the plasma beta increases. This might be due to the larger plasma volume and/or the mitigated Shafranov shift in the vertically elongated configuration.
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  • Wei CHEN, Mitsutaka ISOBE, Kazuo TOI, Kunihiro OGAWA, Xiaodi DU, Masak ...
    2012 Volume 7 Pages 2402079
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    The beta-induced Alfvén eigenmode (BAE) like modes during strong interchange mode, whose mode numbers are m/n = 2/1, have been recently observed for the first time in Large Helical Device (LHD). The first harmonic frequencies of these oscillations range from 30 to 70 kHz, much lower than the toroidal-Alfvén-eigenmode (TAE) frequency, and are provided with the same order of the low-frequency gap induced by finite beta effects. The magnetic fluctuation spectrogram indicates that the BAEs often occur in pairs, and their mode-numbers are m/n = 2/1 and −2/−1. The analysis reveals that the modes propagate poloidally and toroidally in opposite directions, and form standing-wave structures in interchange-mode rest frame. The frequencies of the pair mode are associated with the Te/Ti ratio, and the frequency difference of the pair modes is determined by the frequency of interchange mode. The new finding shed light on the underlying physics mechanism for the excitation of the low frequency Alfvénic fluctuation.
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  • Santosh P. PANDYA, Shwetang N. PANDYA, Zubin SHAIKH, Shamsuddin SHAI ...
    2012 Volume 7 Pages 2402089
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    The Infrared Imaging Video Bolometer (IRVB) is one of the modern plasma imaging diagnostics which provides the measurement of the temporally as well as spatially resolved (2-D/3-D) power profile radiated from plasma devices. The technique has successfully been tested on a large size tokamak (JT-60U) and the same technique is for the first time being utilized for the medium size tokamak ADITYA (R = 75 cm, a = 25 cm, Ip = 80 kA, Te(0)∼350 eV, ‹Ne› ∼ 1.5 × 1013 cm3, BT = 0.7 T), where the plasma shot duration is ∼100 ms and radiated power brightness level is ∼2 W/cm2. The diagnostic is utilizing a 6.4 cm×6.4 cm size and 2.5 µm thick, free standing Platinum foil. A square aperture 0.7×0.7 cm2 of pinhole camera geometry can provide 9×9 bolometer pixel arrays (81 channels) and ∼7 cm of spatial resolution at plasma mid-plane with a 45×45wide field of view. This wide field of view covers two semi-tangential views, on either side of the radial view in the tokamak along with a poloidal view. A medium wave infrared camera having 320×240 focal plane array, 200 Hz frame rate, noise equivalent temperature difference ∼20 mK is used and 10 ms of optimal temporal resolution is experimentally achieved. The present paper discusses the design, developmentand calibration of the system. The performance of the IRVB system for its time response is experimentally investigated and has also been reported here.
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  • Akira MATSUMOTO, Yuji YAMAUCHI, Tomoaki HINO, Kiyohiko NISHIMURA, Yosh ...
    2012 Volume 7 Pages 2402090
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    The hydrogen isotope retention and its removal by inert gas glow discharge for graphite was investigated by residual gas analysis. The amount of retained hydrogen isotope in graphite during the deuterium glow discharge was about 1.0×1017 cm2, which was one order of magnitude larger than that in 316L stainless steel or tungsten. The removal ratio of hydrogen isotope by helium, neon and argon glow discharge cleaning were 49%, 22% and 6% respectively. These removal ratios were similar to those for the stainless steel, but larger than the tungsten. The removalratio in graphitecan be explainedby both the depth distribution of incident deuterium in the materials and the etching depth.
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  • Junichi HIRATSUKA, Akira EJIRI, Makoto HASEGAWA, Yoshihiko NAGASHIMA, ...
    2012 Volume 7 Pages 2402092
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    We have developed a multi-point Thomson scattering system with double-pass configuration for the TST-2 device and have installed new collection optics for the same. Temperature and density can now be measured simultaneously at four points by using four fibers and four polychromators. Herein, we present results of off-axis temperature anisotropy measurements performed with this system, in which no temperature anisotropy beyond the error bar was observed for ohmic plasmas.
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  • Shwetang N. PANDYA, Byron J. PETERSON
    2012 Volume 7 Pages 2402095
    Published: July 26, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    Infrared Imaging Video Bolometers (IRVBs) are successfully being used to study the three dimensional impurity radiation distribution from the LHD plasma. IRVBs can serve as a promising diagnostic for studying the radiation structures of detached plasmas in LHD and hence a comparison can be established with theoretical models. A new IRVB system is being designed for the LHD bottom port for better access to the magnetic x-points and to study the 3D radiation structures. The design overview of this new IRVB system is discussed in this paper. The design includes spatial resolution, field of view of the IRVB, sensitivity and signal to noise estimates. Two optical configurations for an infrared periscope are discussed in brief and selection of a catadioptic configuration with a cassegrain telescope is justified. The sensitivity of the existing IRVBs is expected to increase 5 fold by the addition of this IR periscope.
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  • Hiroe IGAMI, Shin KUBO, Takashi SHIMOZUMA, Yasuo YOSHIMURA, Hiromi TAK ...
    2012 Volume 7 Pages 2402110
    Published: September 13, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    Electron cyclotron heating (ECH) using electron Bernstein waves (EBWs) was studied in the large helical device (LHD). Oblique launching of the slow extraordinary (SX-) mode from the high field side and oblique launching of the ordinary (O-) mode from the low field side were adopted to excite EBWs in the LHD by using electron cyclotron (EC) wave antennas installed apart from the plasma surface. Increases in the stored energy and electron temperature were observed for both cases of launching. These launching methods for ECH using EBWs (EBWH) is promising for high-density operation in future helical fusion devices instead of conventional ECH by normal electromagnetic modes.
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  • Hiroshi IDEI, Hideki ZUSHI, Kazuaki HANADA, Evgeniya KALINNIKOVA, Kazu ...
    2012 Volume 7 Pages 2402112
    Published: September 13, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    A CW phased-array antenna system for electron cyclotron/Bernstein wave heating and current drive (ECWH/CD, EBWH/CD) experiments was developed in the QUEST. The antenna was designed to excite an elliptically polarized pure O-mode wave in oblique injection for the O-X-B mode conversion scenario, and its good performance was confirmed at a high power level. Long pulse discharges with a plasma current of 10 kA and 15 kA were non-inductively attained for 37 s and 20 s, respectively, with only radio frequency (RF) power. Divertor configurations were also obtained in the RF-sustained plasmas. A new operational window for sustained plasma current was observed in the high-density plasma with a higher RF incident power. Two new heating and current drive systems with an 8.56 GHz klystron and a 28 GHz gyrotron are being prepared to conduct CW EBWH/CD experiments in the high-density plasma.
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  • Alexer V. MELNIKOV, Carlos HIDALGO, Takeshi IDO, Akihiro SHIMIZU, Aki ...
    2012 Volume 7 Pages 2402114
    Published: September 13, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    Direct measurements of the electric potential φ, using the Heavy Ion Beam Probing, have been undertaken in the T-10 tokamak, and in the helical devices with various magnetic topology: TJ-II, CHS and LHD. L-mode plasmas were considered. Despite the large differences in machine sizes, heating methods and the topology of the magnetic field, the observed φ shows the striking similarities: (i) Similar magnitudes of Er; (ii) For low densities, ne <0.5×1019 m−3, φ is positive, and an increase in ne is associated with the decrease of positive φ and formation of a negative Er; (iii) For higher densities, ne >(0.5-1)×1019 m−3, both φ and Er tends to be negative despite the use of different heating methods: Ohmic and ECR heating in T-10, ECRH and/or NBI in TJ-II, CHS and LHD; (iv) Application of ECRH, causing a rise in Te, results in more positive values for φ and Er. The analysis show that the main features of the φ dependences on the ne and Te agree with neoclassical predictions on the four devices within experimental and simulation precisions.
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  • Makoto HASEGAWA, Kozo YAMAZAKI, Hideki ARIMOTO, Tetsutarou OISHI, Reiy ...
    2012 Volume 7 Pages 2402116
    Published: September 13, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    TOKASTAR-2 is a small tokamak-helical hybrid device which can generate tokamak and helical configurations independently. In tokamak discharge experiment, the conductive shell was installed to increase plasma current by controlling the displacement of ohmically heated (OH) plasma. The suppression of the vertical displacement was demonstrated, but the OH plasma was still located slightly above the mid plane. To compensate this displacement, the balance between up and down vertical field coil currents should be adjusted. In addition, the construction of additional helical field coils is planned to form closed vacuum magnetic surfaces. The magnetic field line tracing analysis was carried out to determine the detailed shape and location of additional helical field coils. From the simulation, it was clarified that the location of magnetic surfaces and the averaged value of rotational transform can be controlled by adjusting coil current ratios.
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  • Katsuhiro HOSOI, Yousuke NAKASHIMA, Shinji KOBAYSHI, Nobuhiro NISH ...
    2012 Volume 7 Pages 2402126
    Published: September 13, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    Results of supersonic molecular beam injection (SMBI) into GAMMA 10 are described. By analyzing the two-dimensionalimage of the emission captured by a high-speedcamera, we investigated neutral transport during SMBI. The experimental results show that the degree of diffusion of the injected neutral particles decreases with increasing plenum pressure. By applying a three-dimensional Monte-Carlo simulation to GAMMA 10, we analyze the neutral-particle transport. The simulation given under the initial conditions of the conventional gas puffing could not reproduce the experimental results. Compared with experimental results, the results of simulation were too diffusive. The experimental SMBI results were roughly reproduced under more squeezed divergence angle of injected particles than that of a cosine distribution. These results reveal a difference between divergence angles for particles launched via SMBI and via conventional gas puffing.
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  • Yasuyuki FUJIKAWA, Tomohiko ASAI, Midori GOUDA, Tsutomu TAKAHASHI, Lor ...
    2012 Volume 7 Pages 2402130
    Published: September 13, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    Strong toroidal flow is spontaneously generated in a field-reversed configuration (FRC) plasma. It is continuously accelerated during and after the formation phase. The centrifugal force resulting from the toroidal flow causes deformation of the toroidal cross section, with toroidal mode number n = 2. The radial profile of this self generated toroidal flow has previously been described as rigid rotor (RR) in form, i.e., showing uniform angular velocity. However, the toroidal flow profile observed in these experiments indicates the existence of flow shear. In this work, reconstruction of such a profile, utilizing a modified Abel inversion technique, has been performed, and the resulting detailed toroidal flow profile, including time evolution, has been investigated.
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  • Takuro YOKOYAMA, Makoto ICHIMURA, Ryuya IKEZOE, Yumeto UGAJIN, Toru IW ...
    2012 Volume 7 Pages 2402136
    Published: October 15, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    On GAMMA10, waves in Ion-Cyclotron Range of Frequency (ICRF) are used to produce initial plasmas, heat plasmas and keep magneto-hydrodynamic (MHD) stability. High performance plasmas in the minimum-B configuration supply MHD stability. In order to enhance plasma heating, we introduce an ICRF system for heating plasmas in the anchor cell and evaluate its antenna loading. Changing the antenna shape is expected to improve antenna loading. In the experiment, we confirm to increase the antenna loading by changing the antenna shape from simple bar-type to the double elliptic arc type.
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  • Tetsuo OZAKI, Naoki TAMURA, Tetsuo SEKI, Hiroshi KASAHARA, Shigeru SUD ...
    2012 Volume 7 Pages 2402138
    Published: October 15, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    The pellet charge exchange technique (PCX), which is a combination of the compact neutral particle analyzer and an impurity pellet, is a unique method to observe the radial energetic particle distribution. There are not only charge exchange reactions between the hydrogen in the pellet and a proton, but also between the partially ionized carbon in the pellet and the proton. The neutralization factor from energetic ion to neutral particle could be deduced from the electron temperature and the electron density of the pellet cloud. The radial profiles of energetic particle distribution were measured and compared in various ion cyclotron resonance heating (ICH) plasmas. The energetic particle flux significantly increased at the resonance layer created by the ICH. PCX provides more precise information about the resonance layer than conventional neutral particle diagnostics.
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  • Chunfeng DONG, Shigeru MORITA, Motoshi GOTO, Erhui WANG
    2012 Volume 7 Pages 2402139
    Published: October 15, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    A space-resolved extreme ultraviolet (EUV) spectrometer has been upgraded by extending the wavelength range to 30-650 Å to explore impurity line emissions existing at shorter and longer wavelength sides. The absolute intensity calibration is implemented for measurement in the extended wavelength based on bremsstrahlung profiles simultaneously measured in EUV and visible ranges. For the purpose a wider entrance slit of 200 µm and a wider space-resolved slit of 1.0 mm are adopted to increase the number of photons to the spectrometer. As a result, the bremsstrahlung intensity can be enhanced by order of magnitude. A centrally peaked high-density discharge at ne(0) ≥ 1014 cm−3 is also used for the accurate calibration. Thus, the calibration becomes possible, even in longer wavelength side at λ ≥ 400 Å. The result at shorter wavelength range of 30-90 Å shows a flat calibration factor, suggesting sudden changes of holographic grating efficiency and CCD detection efficiency, while the result at longer wavelength side of λ ≥ 400 Å shows a simple extension of the previous calibration factor.
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  • Tokimasa KAWABATA, Daisuke TOKAI, Katsuhiko NISHIMURA, Yoshimitsu HISH ...
    2012 Volume 7 Pages 2402150
    Published: November 22, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    MgB2 superconducting wires are interesting as the alternative conductors of Nb-based superconducting wires applied for the advanced nuclear fusion reactor because of the decay time of the induced radioactivity. However, MgB2 is difficult for practical use because of its unworkable and lower critical current density (JC) in a high magnetic field than Nb-based superconductive materials. We have developed the original method of three-dimensional penetration casting (3DPC) to fabricate the MgB2/Al composite materials. In the composite materials we made, MgB2 particles dispersed in the matrix uniformly. This makes these composite materials can be processed by machining, extrusion and rolling. And the TC of the made composite materials was determined by electrical resistivity and magnetization to be 37∼39 K. In this work, we made composite materials with ground MgB2 particles with the purpose of extruding thinner wires of composite material. Furthermore, we successfully produced ϕ1 mm wires and also changed the matrix from pure Al to Al-In alloy. JC of composite materials with the matrix of Al-In alloy was calculated with the width of the magnetic hysteresis based on the Extended Bean Model. The result was better than that of MgB2/Al composite material without Indium. Microstructures of these samples had been confirmed by SEM observation.
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  • Naoyuki SHINODA, Naoko ASHIKAWA, Yuji NOBUTA, Yuji YAMAUCHI, Tomoaki H ...
    2012 Volume 7 Pages 2402155
    Published: November 22, 2012
    Released: September 02, 2013
    JOURNALS FREE ACCESS
    The gas desorption behavior, and the amounts of retained gases and deposited impurities in the first wall during the 13th experimental campaign in the Large Helical Device (LHD) have been evaluated using a material probes technique. The desorption behavior of hydrogen and helium depended on the atomic composition of deposited impurities. The amount of retained hydrogen was large in the vicinity of the anodes used for the glow discharge conditioning (GDC). The amount of retained helium was small near the anodes in this campaign. The toroidal dependence on the amount of retained gas corresponded to the total time for the GDC and the gas species used for glow discharge in the final stage.
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  • Masayuki YOKOYAMA, Arimitsu WAKASA, Ryosuke SEKI, Masahiko SATO, Saday ...
    Type: Regular Articles
    2012 Volume 7 Pages 2403011
    Published: February 24, 2012
    Released: March 09, 2012
    JOURNALS FREE ACCESS
    The integrated transport code for helical plasmas, TASK3D, has been developed both by modifying modules in TASK to be applicable to three-dimensional magnetic configurations, and by adding new modules for stellarator-heliotron specific physics and incorporating three-dimensional equilibria. In this paper, these module developments so far are collectively introduced, and recent progress on the applications of TASK3D to heat transport analyses of LHD plasmas is introduced.
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  • Kinya SAITO, Katsuji ICHIGUCHI, Ryuichi ISHIZAKI
    2012 Volume 7 Pages 2403032
    Published: May 10, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Magnetohydrodynamics (MHD) equilibria including static magnetic islands for the reduced MHD equations in a straight heliotron plasma are calculated. The equilibria are obtained as the solution of the coupled equations of the constant pressure along each field line and the force balance. The former and the latter equations are solved by means of a field line tracing method and a relaxation method, respectively. There exist two kinds of solutions. One is the equilibrium of which the pressure profile is flat at the O-point and steep at the X-point. In this case, the pressure gradient is discontinuous at the separatrix of the magnetic island. The other is the equilibrium of which the pressure profile is flat at not only the O-point but also the X-point. In the case, the pressure gradient is continuous at the separatrix.
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  • Fusaki P. IIZIMA, Toshiki TAKAHASHI, Takayuki WATANABE , Tomohiko ...
    2012 Volume 7 Pages 2403057
    Published: June 07, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Electron-fluid perturbation fields of a field-reversed configuration plasma is investigated by assuming the source of a electromagnetic wave is the electron current fluctuation. Electron trajectories in the prescribed perturbation field are calculated, and the toroidal flow velocity and velocity distribution and estimated by the particle-in-cell method. It is found that electrons are heated and enhancement of the end-loss of electrons is observed when the perturbation field is present.
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  • Dick HOGEWEIJ, Jean-Francois ARTAUD, Tom CASPER, Jonathan CITRIN, Fred ...
    2012 Volume 7 Pages 2403063
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    This paper reports on a systematic effort to optimize the current ramp-up phase for the ITER hybrid scenario, and to assess the sensitivity of the results to the assumptions made.
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  • Hideaki MATSUURA, Daisuke SAWADA, Yasuyuki NAKAO
    2012 Volume 7 Pages 2403076
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    The effect of the nuclear plus interference (NI) scattering on the slowing-down distribution functions of energetic-ions, e.g., protons produced by 3He(d,p)4He reactions in a D3He plasma and an energetic deuterium beam injected into a DT plasma, are examined using the Boltzmann-Fokker-Planck model. As a result of the acceleration of the slowing-down process of energetic ions due to NI scattering, the magnitude of the energetic component is reduced compared with the case when NI scattering is ignored. The degree of the reduction and its energy range are quantitatively evaluated for various plasma conditions.
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  • Andreas BIERWAGE, Nobuyuki AIBA, Yasushi TODO, Wenjun DENG, Masao ISHI ...
    2013 Volume 7 Pages 2403081
    Published: July 26, 2013
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    The effect of bulk pressure on the nonlinear dynamics of energetic particle modes (EPM) in a neutral-beam-driven JT-60U dischargeis examined through nonlinear hybrid (MHD + particle) simulations with realistic values of the plasma beta and in realistic flux surface geometry. In the scenario studied, the linear EPM growth rate is 20% higher in the finite-beta compared to the zero-beta case, but compressibility stabilizes the mode by roughly the same amount. In the finite-beta case, the nonlinear frequency shift and the radial spreading/propagation of the mode are affected by the beta-induced gap in the shear Alfvén continuum. Although the evolution of the modes is affected by bulk pressure, compressibility and geometry, the overall energetic ion transport during the first few 100 Alfvén times following the saturation of the EPM is comparable in all cases studied.
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  • Kaoru OHYA, Yoshio SONEDA
    2013 Volume 7 Pages 2403083
    Published: July 26, 2013
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    To study tritium retention in a divertor target made of tungsten, thermal processes of hydrogen isotopes, including implantation, diffusion, trapping and detrapping, and surface recombination, are modeled for ITER plasma configuration. The material parameters governing the processes are estimated by simulating an existing TDS experiment by using the model. In case of the inner target, dominant retention mechanism is the trapping in the deep trap and most of the T atoms are kept in the trap even after discharge. Mobile T atoms dominate the T retention in the outer target due to its high temperature, the amount of which is ten times greater than that in the inner target. The T retention after a discharge of 400 s is estimated to be tens of mg, resulting in 10000 or more discharges after which a T safety limit of 700 g is reached. Nevertheless, it strongly depends on the trap concentration in the target.
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  • Satoshi TOGO, Makoto NAKAMURA, Yuichi OGAWA, Katsuhiro SHIMIZU, Tomono ...
    2012 Volume 7 Pages 2403087
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Operation under partially detached divertor (PDD) plasmas is a hopeful way in order to reduce the divertor heat load in the next generation tokamaks. The physical mechanism of PDD plasmas, however, has not fully been understood yet. We have studied them with a multi-layer one-dimensional divertor model. The PDD plasmas are successfully reproduced by introducing a neutral gas puffing model. Effect of the cross-field heat transport on the PDD plasmas is investigated. It is found that cross-field heat transport both in the SOL region and in the divertor region prevents detachment fronts from moving upstream in a detached flux tube.
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  • Isao KATANUMA, Shun MASAKI, Shuhei SATO, Kazuto SEKIYA, Makoto ICHIMUR ...
    2012 Volume 7 Pages 2403093
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    The numerical code for calculation of ion orbits was developed in order to calculate the ion orbits in the divertor and dipole regions of the GAMMA10 A-divertor. The flux coordinates (ψ, θ, χ) have been adopted, where the magnetic field B is represented by B = ∇ψ×∇θ = ∇χ. It is found that ion orbits behave chaotic around the magnetic null.
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  • Hideo SUGAMA, Tomohiko WATANABE, Masanori NUNAMI, Shinsuke SATAKE, Sei ...
    2012 Volume 7 Pages 2403094
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Drift kinetic and gyrokinetic theories and simulations are powerful means for quantitative predictions of neoclassical and anomalous transport fluxes in helical systems such as the Large Helical Device (LHD). The δf Monte Carlo particle simulation code, FORTEC-3D, is used to predict radial profiles of the neoclassical particle and heat transport fluxes and the radial electric field in helical systems. The radial electric field profiles in the LHD plasmas are calculated from the ambipolarity condition for the neoclassical particle fluxes obtained by the global simulations using the FORTEC-3D code, in which effects of ion or electron finite orbit widths are included. Gyrokinetic Vlasov simulations using the GKV code verify the theoretical prediction that the neoclassical optimization of helical magnetic configuration enhances the zonal flow generation which leads to the reduction of the turbulent heat diffusivity χi due to the ion temperature gradient (ITG) turbulence. Comparisons between results for the high ion temperature LHD experiment and the gyrokinetic simulations using the GKV-X code show that the χi profile and the poloidal wave number spectrum of the density fluctuation obtained from the simulations are in reasonable agreements with the experimental results. It is predicted theoretically and confirmed by the linear GKV simulations that the E × B rotation due to the background radial electric field Er can enhance the zonal-flow response to a given source. Thus, in helical systems, the turbulent transport is linked to the neoclassical transport through Er which is determined from the ambipolar condition for neoclassical particle fluxes and influences the zonal flow generation leading to reduction of the turbulent transport. In order to investigate the Er effect on the regulation of the turbulent transport by the zonal flow generation, the flux-tube bundle model is proposed as a new method for multiscale gyrokinetic simulations.
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  • Emi NARITA, Tomonori TAKIZUKA, Nobuhiko HAYASHI, Takaaki FUJITA, Shuns ...
    2012 Volume 7 Pages 2403102
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    In order to improve the prediction capability of confinement properties in burning plasmas with intensive electron heating, we have re-visited the DB3v10 International H-mode Confinement Database with emphasis on the temperature ratio Te/Ti and considerations on kinetic profiles. It was thereby found that the impact of Te/Ti is more apparent for discharges with peaked density profiles. Namely, HH factor improves with an increase of peakedness in the density profile for Te/Ti < 1, whereas it tends to deteriorate with the density peaking for Te/Ti > 1. The confinement scaling with a contribution of Te/Ti was also elaborated. In addition, the influence of Te/Ti described above was examined qualitatively with GS2 and GLF23 codes, which provided results corroborating the performed regression analysis, indicating the interplay of ITG and TEM in the turbulence transport.
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  • Kazuyoshi HADA, Kazunobu NAGASAKI, Kai MASUDA, Ryota KINJO, Shunsuke I ...
    2012 Volume 7 Pages 2403104
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Plasma start-up assisted by electron cyclotron resonance heating (ECRH) pre-ionizationis theoretically studied for the superconducting tokamak JT-60SA by using a zero-dimensional (0-D) model. Because the toroidal electric field is limited to 0.5 Vm−1, we clarify the conditions for a robust plasma initiation. Five temporal equations are solved for a spatially-uniform plasma: the electron and neutral density equations, the electron and ion energy density equations, and the electric circuit equation. The numerical calculation results show that an absorbed ECRH power of 150 kW is required to start up the plasma, assuming an initial neutral density of 3.0×1018 m−3, and that reducing the oxygen and carbon impurity densities facilitates successful start-up. We discuss the dependence of the absorbed ECRH power on the neutral density and impurities. The simulation qualitatively reproduces experimental results from JT-60U.
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  • Seiya NISHIMURA, Shinichiro TODA, Masatoshi YAGI, Yoshiro NARUSHIMA
    2012 Volume 7 Pages 2403107
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Influence of external resonant magnetic perturbation (RMP) on a helical plasma is numerically investigated, using a set of reduced magnetohydrodynamic equations. Coexistence of the resistive interchange mode and RMP is simulated. In nonlinear simulations, saturated magnetic islands by the RMP typically show two states: oscillating small islands and locked large islands. In the former state, rotation of magnetic islands by neoclassical transport-driven poloidal flows disturbs growth of islands. On the other hand, in the latter state, locking of poloidal flows due to the RMP and growth of islands occur simultaneously. It is found that the curvature driven current enhances magnetic reconnection, and width of the large islands overcomes that of vacuum islands.
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  • Daniel RABURN, Atsushi FUKUYAMA
    2012 Volume 7 Pages 2403108
    Published: July 26, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Equilibrium flows and 3D effects can significantly impact plasma stability and energy confinement. Further, in equilibria with flow, FLR effects can play an important role. Presently, there exist a number of codes which can calculate MHD equilibria with a subset of the above effects, such as: the FLOW code [L. Guazzotto, R. Betti, J. Manickam and S. Kaye, Phys. Plasmas 11(2), 604 (2004)], the PIES code [H.S. Greenside, A.H. Reiman and A. Salas, J. Comput. Phys. 81(1), 102 (1989)], and the ItoGSEQ code [D. Raburn and A. Fukuyama, Phys. Plasmas 17(12), 122504 (2010)]. Using insights gained from these codes, the concept for a new code for calculation of 3D MHD equilibria with flow and FLR effects has been developed; the code is called the Kyoto ITerative Equilibrium Solver (KITES).
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  • Orso MENEGHINI, Syunichi SHIRAIWA, Ronald PARKER
    2012 Volume 7 Pages 2403111
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    In this paper, we introduce the use of Continuous-Wavelet-Transform (CWT) to postprocess full-wave fields of Lower Hybrid (LH) waves which have been generated using the LHEAF code. Compared to the Fourier transform, the CWT has the appealing property of yielding information as to the spatial location of spectral modes. Using a complex-Morlet CWT, the complicated full-wave field pattern is decomposed into its spectral components parallel to the static magnetic field n. In general, the CWT of the LHEAF full-wave fields shows that the local wave spectrum broadens as the waves propagate through the plasma and after reflection off the low density cutoff or the vacuum vessel walls. The goal of this analysis is to provide a tool to assess the importance of full-wave effects on the transformation of the wave n spectrum which governs the LH power absorption and driven currents.
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  • Tsuguhiro WATANABE
    2012 Volume 7 Pages 2403113
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    A new winding law for the continuous helical coils is proposed for Large Helical Device (LHD) type fusion reactors to satisfy the requirements for a wide blanket space and large plasma volume. Helical coils wound along the geodesic line of a torus with an elongated cross section can produce a magnetic configuration having a D-shaped magnetic surface with a magnetic well in the core region and high magnetic shear in the peripheral regions. The DT alpha particle confinement performance is greatly improved by increasing the elongation factor κ of the cross section of the winding frame for the helical coils. The results suggest that a smaller LHD-type fusion reactor can be realized.
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  • Naoki MIZUGUCHI, Akio SANPEI, Shinichi FUJITA, Kensuke OKI, Haruhiko ...
    2012 Volume 7 Pages 2403117
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Nonlinear three-dimensional magnetohydrodynamic (MHD) simulations were applied to a reversed-field pinch (RFP) plasma to reveal the physical mechanism of the formation of helical structures such as the so-called quasi-single helicity and single helical axis states. The simulations were executed using the MHD Infrastructure for Plasma Simulation (MIPS) code in a realistic experimental geometry of the REversed field pinch of Low-Aspect ratio eXperiment (RELAX) device with reconstructed initial equilibria calculated by the RELAXFit code. Long-term evolutions showed remarkable formation of n = 4 structures as a result of the dominant growth of resistive modes. The resultant relaxed helical state consists of a bean-shaped, hollow pressure profile in the poloidal cross section for both the cases of resonant and non-resonant triggering instabilities.
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  • Junji MANO, Kozo YAMAZAKI, Tetsutarou OISHI, Hideki ARIMOTO , Tatsuo S ...
    2012 Volume 7 Pages 2403124
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    For the achievement of steady-state fusion power plant, non-inductively current-driven plasma operation should be maintained in tokamak fusion reactors. Total non-inductive current is a summation of bootstrap current proportional to the plasma pressure gradient and externally driven non-inductive current such as neutral beam driven current. Especially in order to establish a commercial reactor, it is necessary to reduce the amount of external current-drive power and to maintain the majority of the plasma current with bootstrap current. Burning plasma has high autonomy, so the change in current density profile including changes in particle and heat transports should be checked. In this study time-evolution analysis of the current density profile for burning plasmas in the ITER machine has been conducted by using 2.0-dimensional equilibrium, 1.5-dimensional-transport code (TOTAL code). Here current-diffusive ballooning mode model was adopted as a heat transport model. It is concluded that external current-drive is required both in the center and near the periphery of the plasma in order to maintain steady-state profiles of temperature and density with high bootstrap current fraction.
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  • Xiaobin DING, Izumi MURAKAMI, Daiji KATO, Hiroyuki A. SAKAUE, Fumihiro ...
    2012 Volume 7 Pages 2403128
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    A detailed collisional radiative model of W27+ ions was constructed based on the atomic data calculated by relativistic atomic properties software Flexible Atomic Code. The strong electric dipole (E1) transitions mainly comes from the 4f → 4d transition in W27+ ions with wavelength falls into VUV region (4.6 - 5.1 nm), while the wavelength of magnetic dipole (M1) transition among the fine structures of the first excited states falls into the visible optical region. Synthetic spectra in both regions are given theoretically with plasma condition in EBIT for experiment reference. Finally, the dependence of the intensity ratio on the electron density is provided as a potential diagnostic tool of Maxwellian plasmas.
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  • Gakushi KAWAMURA, Izumi MURAKAMI, Yukihiro TOMITA, Suguru MASUZAKI
    2012 Volume 7 Pages 2403129
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Increasing heat load to plasma-facing walls in future fusion devices and reactors could exceed the engineering limit of the material if simple scaling is applied in size of device to realize sufficient energy confinement time. One of possible means to remove the heat in plasma is impurity gas puffing. In order to investigate the plasma response to the radiation cooling, a one dimensional steady-state two-fluid model has been developed to describe SOL plasma of LHD. Model equations were solved numerically for various neon density and three types of SOL plasma. Maximum neon density above which plasma does not sustain is found. Significant reduction of temperature and heat flux onto the divertor plate are found. It is confirmed that the neon gas puffing is an effective technique to reduce the heat load onto divertor plates.
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  • Shunsuke IDE, Nobuhiko HAYASHI, Mitsuru HONDA, Hajime URANO, Takahiro ...
    2012 Volume 7 Pages 2403131
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    JT-60SA will be operated in several operational domains to pursue its objectives, to support researches on ITER and develop physics and engineering basis towards DEMO reactor. Evolution and tailoring of the current profile, or the safety factor (q) profile in other words, is important in preparation for plasmas expected in the operational domains. Especially in the high normalized pressure (βN) domain, tailoring of the q profile is indispensable to achieve high performance. In this paper, evolution of the q profile during the current ramp-up in a candidate plasma for a steady-state high βN and modification of the q profile by means of ECRF are examined by modeling simulation. Impact of the target q profile modification on the energy confinement is also discussed.
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  • Shinobu NAKAZAWA, Daichi ARAI, Toshiya MORIMURA, Daisuke MIYAGI, Makot ...
    2012 Volume 7 Pages 2403143
    Published: October 15, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Cable-in-Conduit-Conductor (CICC) is used for the international thermonuclear fusion experimental reactor (ITER) toroidal field (TF) coils. But the critical current of the CICC is measured lower than expected one. This is partly explained by unbalanced current distribution caused by inhomogeneous contact resistances between strands and copper sleeves at joints. Current density in some strands reaches the critical under unbalanced current, and the quench is occurred under smaller transport current than expected one. In order to investigate the contact resistances, we measure the three-dimensional positions of all strands inside the CICC for Large Helical Device (LHD) poloidal field (PF) outer vertical (OV) coil, and evaluate contact parameters such as number and lengths of strands which contact with a copper sleeve. Then, we simulate the strand positions in the CICC using the numerical code which we developed, and compare the contact parameters which evaluated from the measured strand positions and the simulated ones. It is found that the both results are in good agreement, and the developed numerical model is useful for evaluation of the contact parameters. We apply the code to various CIC conductor joints to obtain optimal joint parameters.
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  • Hidemasa OZEKI, Kozo YAMAZAKI, Hideki ARIMOTO, Tetsutarou OISHI, Tatsu ...
    2012 Volume 7 Pages 2403144
    Published: October 15, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Six types of spherical tokamak-stellarator hybrid configurations with simple shaped coils “TOKASTAR”, are proposed and analyzed in terms of magnetic flux surface, equilibrium and fast particle confinement. It was found that TOKASTAR can produce flux surfaces with low averaged aspect ratio. The averaged rotational transform are low but local value is relatively high, especially at the outboard side. In the equilibrium beta limit analysis it was clarified that TOKASTAR can achieve high equilibrium beta with relatively low plasma current. In the fast particle confinement analysis, it was found that the fraction of confined alpha particles in the reactor-sized TOKASTAR is 40∼60%.
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  • Daiki KURITA, Kozo YAMAZAKI, Hideki ARIMOTO, Tetsutarou OISHI, Tatsuo ...
    2012 Volume 7 Pages 2403149
    Published: November 22, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    For the stabilization of neoclassical tearing mode (NTM), Electron Cyclotron Current Drive (ECCD) is used. The change of the EC control efficiency depends on EC modulation width and EC injection phase lag from the O-point of magnetic island. In this work, NTM stabilization by ECCD is analyzed using 1.5-dimensional transport code TOTAL, in which the time variation of magnetic island is described by the modified Rutherford equation. NTM in ITER can be stabilized when the EC phase lag is smaller than 10% and the EC modulation width is around 20%, when the time-averaged EC current and power is fixed.
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  • Keita SETO, Hideo NAGATOMO, James KOGA, Kunioki MIMA
    Type: Regular Articles
    2012 Volume 7 Pages 2404010
    Published: February 24, 2012
    Released: March 09, 2012
    JOURNALS FREE ACCESS
    In the near future, the intensity of the ultra-short pulse laser will reach to 1022 W/cm2. When an electron is irradiated by this laser, the electron's behavior is relativistic with significant bremsstrahlung. This radiation from the electron is regarded as the energy loss of electron. Therefore, the electron's motion changes because of the kinetic energy changing. This radiation effect on the charged particle is the self-interaction, called the “radiation reaction” or the “radiation damping”. For this reason, the radiation reaction appears in laser electron interactions with an ultra-short pulse laser whose intensity becomes larger than 1022 W/cm2. In the classical theory, it is described by the Lorentz-Abraham-Dirac (LAD) equation. But, this equation has a mathematical difficulty, which we call the “run-away”. Therefore, there are many methods for avoiding this problem. However, Dirac's viewpoint is brilliant, based on the idea of quantum electrodynamics. We propose a new equation of motion in the quantum theory with radiation reaction in this paper.
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  • Shinya NOZAKI, Atsushi KINJO, Shinsuke FUJIOKA, Rumiko AZUMA, Yen-Wei ...
    2012 Volume 7 Pages 2404120
    Published: September 13, 2012
    Released: September 26, 2013
    JOURNALS FREE ACCESS
    Penumbral imaging technique can be applied to highly penetrating radiations such that of as neutrons. In penumbral imaging, the source image can be recovered from its penumbral image by deconvolution. The method is an efficient imaging technique for fast ignition research. However, the γ rays produced by the fast-heating laser pollute the penumbral image as noise. Conventional deconvolution methods like the Wiener filter cannot obtain a clear reconstructed image from noisy penumbral image. In this paper, we proposea new reconstruction method by principal component analysis (PCA). The method can efficiently remove the noise by “training” images obtained from other experiments. We used the (2D)2PCA method as a noise reduction method, which is one of the PCA methods. The efficacy of the proposed method is demonstrated by computer simulation.
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  • Hideya NAKANISHI, Setsuo IMAZU, Masaki OHSUNA, Mamoru KOJIMA, Miki NON ...
    Type: Regular Articles
    2012 Volume 7 Pages 2405007
    Published: February 17, 2012
    Released: March 09, 2012
    JOURNALS FREE ACCESS
    To deal with endless data streams acquired in LHD steady-state experiments, the LHD data acquisition system was designed with a simple concept that divides a long pulse into a consecutive series of 10-s “subshots”. Latest digitizers applying high-speed PCI-Express technology, however, output nonstop gigabyte per second data streams whose subshot intervals would be extremely long if 10-s rule was applied. These digitizers need shorter subshot intervals, less than 10-s long. In contrast, steady-state fusion plants need uninterrupted monitoring of the environment and device soundness. They adopt longer subshot lengths of either 10 min or 1 day. To cope with both uninterrupted monitoring and ultra-fast diagnostics, the ability to vary the subshot length according to the type of operation is required. In this study, a design modification that enables variable subshot lengths was implemented and its practical effectiveness in LHD was verified.
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