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  • AIP Publishing  (43)
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  • 1
    Online Resource
    Online Resource
    Thermal transport barrier in heliotron-type devices (Large Helical Device and Compact Helical System)
    AIP Publishing ; 2000
    In:  Physics of Plasmas Vol. 7, No. 5 ( 2000-05-01), p. 1802-1808
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 7, No. 5 ( 2000-05-01), p. 1802-1808
    Abstract: In the discharges of the Large Helical Device [O. Motojima et al., Proceedings of the 16th Conference on Fusion Energy, Montreal, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 3, p. 437], a significant enhancement of the energy confinement has been achieved with an edge thermal transport barrier, which exhibits a sharp gradient at the edge. Key features associated with the barrier are quite different from those seen in tokamaks (i) almost no change in particle (including impurity) transport, (ii) a gradual formation of the barrier, (iii) a very high ratio of the edge temperature to the average temperature, (iv) no edge relaxation phenomenon. In the electron cyclotron heating (ECH) heated discharges in the Compact Helical System [K. Matsuoka et al., in Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, France, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 411] , the internal electron transport barrier has been observed, which enhances the central electron temperature significantly. High shear of the radial electric field appears to suppress the turbulence in the core region and enhance the electron confinement there.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.874001
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
    detail.hit.zdb_id: 1472746-8
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  • 2
    Online Resource
    Online Resource
    Compatibility between high energy particle confinement and magnetohydrodynamic stability in the inward-shifted plasmas of the Large Helical Device
    AIP Publishing ; 2002
    In:  Physics of Plasmas Vol. 9, No. 5 ( 2002-05-01), p. 2020-2026
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 9, No. 5 ( 2002-05-01), p. 2020-2026
    Abstract: The experimentally optimized magnetic field configuration of the Large Helical Device [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)], where the magnetic axis is shifted inwa rd by 15 cm from the early theoretical prediction, reveals 50% better global energy confinement than the prediction of the scaling law. This configuration has been investigated further from the viewpoints of high energy particle confinement and magnetohydrodynamic (MHD) stability. The confinement of high energy ions is improved as expected. The minority heating of ion cyclotron range of frequency was successful and the heating efficiency was improved by the inward shift. The confinement of passing particles by neutral beam injection was also improved under low magnetic field strength, and there could be obtained an almost steady high beta discharge up to 3% in volume average. This was a surprising result because the observed pressure gradient exceeded the Mercier unstable limit. The observed MHD activities became as high as beta but they did not grow enough to deteriorate the confinement of high energy ions or the performance of the bulk plasma, which was still 50% better than the scaling. According to these favorable results, better performance would be expected by increasing the heating power because the neoclassical transport can also be improved there.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.1448345
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2002
    detail.hit.zdb_id: 1472746-8
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  • 3
    Online Resource
    Online Resource
    Improved plasma performance on Large Helical Device
    AIP Publishing ; 2001
    In:  Physics of Plasmas Vol. 8, No. 5 ( 2001-05-01), p. 2002-2008
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 8, No. 5 ( 2001-05-01), p. 2002-2008
    Abstract: Since the start of the Large Helical Device (LHD) experiment, various attempts have been made to achieve improved plasma performance in LHD [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)]. Recently, an inward-shifted configuration with a magnetic axis position Rax of 3.6 m has been found to exhibit much better plasma performance than the standard configuration with Rax of 3.75 m. A factor of 1.6 enhancement of energy confinement time was achieved over the International Stellarator Scaling 95. This configuration has been predicted to have unfavorable magnetohydrodynamic (MHD) properties, based on linear theory, even though it has significantly better particle-orbit properties, and hence lower neoclassical transport loss. However, no serious confinement degradation due to the MHD activities was observed, resolving favorably the potential conflict between stability and confinement at least up to the realized volume-averaged beta 〈β〉 of 2.4%. An improved radial profile of electron temperature was also achieved in the configuration with magnetic islands, minimized by an external perturbation coil system for the Local Island Divertor (LID). The LID has been proposed for remarkable improvement of plasma confinement like the high (H) mode in tokamaks, and the LID function was suggested in limiter experiments.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.1344561
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2001
    detail.hit.zdb_id: 1472746-8
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  • 4
    Online Resource
    Online Resource
    Formation of electron internal transport barrier and achievement of high ion temperature in Large Helical Device
    AIP Publishing ; 2003
    In:  Physics of Plasmas Vol. 10, No. 5 ( 2003-05-01), p. 1788-1795
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 10, No. 5 ( 2003-05-01), p. 1788-1795
    Abstract: An internal transport barrier (ITB) was observed in the electron temperature profile in the Large Helical Device [O. Motojima et al., Phys. Plasmas 6, 1843 (1999)] with a centrally focused intense electron cyclotron resonance microwave heating. Inside the ITB the core electron transport was improved, and a high electron temperature, exceeding 10 keV in a low density, was achieved in a collisionless regime. The formation of the electron-ITB is correlated with the neoclassical electron root with a strong radial electric field determined by the neoclassical ambipolar flux. The direction of the tangentially injected beam-driven current has an influence on the electron-ITB formation. For the counter-injected target plasma, a steeper temperature gradient, than that for the co-injected one, was observed. As for the ion temperature, high-power NBI (neutral beam injection) heating of 9 MW has realized a central ion temperature of 5 keV with neon injection. By introducing neon gas, the NBI absorption power was increased in low-density plasmas and the direct ion heating power was much enhanced with a reduced number of ions, compared with hydrogen plasmas.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.1560613
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2003
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  • 5
    Online Resource
    Online Resource
    Ion cyclotron range of frequency heating experiments on the large helical device and high energy ion behavior
    AIP Publishing ; 2001
    In:  Physics of Plasmas Vol. 8, No. 5 ( 2001-05-01), p. 2139-2147
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 8, No. 5 ( 2001-05-01), p. 2139-2147
    Abstract: Ion cyclotron range of frequency (ICRF) heating experiments on the Large Helical Device (LHD) [O. Motojima et al. Fus. Eng. Des. 20, 3 (1993)] achieved significant advances during the third experimental campaign carried out in 1999. They showed significant results in two heating modes; these are modes of the ICH-sustained plasma with large plasma stored energy and the neutral beam injection (NBI) plasma under additional heating. A long-pulse operation of more than 1 minute was achieved at a level of 1 MW. The characteristics of the ICRF heated plasma are the same as those of the NBI heated plasma. The energy confinement time is longer than that of International Stellarator Scaling 95. Three keys to successful ICRF heating are as follows: (1) an increase in the magnetic field strength, (2) the employment of an inward shift of the magnetic axis, (3) the installation of actively cooled graphite plates along the divertor legs. Highly energetic protons accelerated by the ICRF electric field were experimentally observed in the energy range from 30 to 250 keV and the tail temperature depended on the energy balance between the wave heating and the electron drag. The transfer efficiency from the high energy ions to the bulk plasma was deduced from the increase in the energy confinement time due to the high energy ions in the lower density discharge, which agrees fairly well with the result obtained by the Monte Carlo simulation. The transfer efficiency is expected to be 95% at an electron density of more than ne=5.0×1019 m−3 even in the high power heating of 10 MW. The accumulation of impurities, e.g., FeXVI and OV was not observed in high rf power and long pulse operation. The well-defined divertor intrinsic to LHD is believed to be useful in reducing the impurity influx.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.1354152
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2001
    detail.hit.zdb_id: 1472746-8
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  • 6
    Online Resource
    Online Resource
    Initial physics achievements of large helical device experiments
    AIP Publishing ; 1999
    In:  Physics of Plasmas Vol. 6, No. 5 ( 1999-05-01), p. 1843-1850
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 6, No. 5 ( 1999-05-01), p. 1843-1850
    Abstract: The Large Helical Device (LHD) experiments [O. Motojima, et al., Proceedings, 16th Conference on Fusion Energy, Montreal, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 3, p. 437] have started this year after a successful eight-year construction and test period of the fully superconducting facility. LHD investigates a variety of physics issues on large scale heliotron plasmas (R=3.9 m, a=0.6 m), which stimulates efforts to explore currentless and disruption-free steady plasmas under an optimized configuration. A magnetic field mapping has demonstrated the nested and healthy structure of magnetic surfaces, which indicates the successful completion of the physical design and the effectiveness of engineering quality control during the fabrication. Heating by 3 MW of neutral beam injection (NBI) has produced plasmas with a fusion triple product of 8×1018 keV m−3 s at a magnetic field of 1.5 T. An electron temperature of 1.5 keV and an ion temperature of 1.4 keV have been achieved. The maximum stored energy has reached 0.22 MJ, which corresponds to 〈β〉=0.7%, with neither unexpected confinement deterioration nor visible magnetohydrodynamics (MHD) instabilities. Energy confinement times, reaching 0.17 s at the maximum, have shown a trend similar to the present scaling law derived from the existing medium sized helical devices, but enhanced by 50%. The knowledge on transport, MHD, divertor, and long pulse operation, etc., are now rapidly increasing, which implies the successful progress of physics experiments on helical currentless-toroidal plasmas.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.873443
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1999
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  • 7
    Online Resource
    Online Resource
    Overview of large helical device diagnostics (invited)
    AIP Publishing ; 2001
    In:  Review of Scientific Instruments Vol. 72, No. 1 ( 2001-01-01), p. 483-491
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 72, No. 1 ( 2001-01-01), p. 483-491
    Abstract: The Large Helical Device (LHD) is the largest helical machine with superconducting coils. Key diagnostics issues for LHD are: (a) capability for multidimensional measurements because of the nonaxisymmetric toroidal plasma; (b) measurements of the electric field; (c) cross check of fundamental parameters using different methods; (d) advanced measurements appropriate for steady-state operation; and (e) a satisfactory data acquisition system. The design and research and development of plasma diagnostics were carried out taking these issues into consideration. As a result, the present status of diagnostics is described: diagnostics for LHD operation, fundamental diagnostics for plasma performance, diagnostics for physics subjects, innovative diagnostics and diagnostics for long-pulse operation. The LHD experiment started in March, 1998. Since then, the development of diagnostics has kept pace with the experimental campaigns.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1310581
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2001
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 8
    Online Resource
    Online Resource
    Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma
    AIP Publishing ; 2000
    In:  Physics of Plasmas Vol. 7, No. 10 ( 2000-10-01), p. 4152-4183
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 7, No. 10 ( 2000-10-01), p. 4152-4183
    Abstract: The bifurcation nature of the electrostatic structure is studied in the toroidal helical plasma of the Compact Helical System (CHS) [K. Matsuoka et al., Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 411]. Observation of bifurcation-related phenomena is introduced, such as characteristic patterns of discrete potential profiles, and various patterns of self-sustained oscillations termed electric pulsation. Some patterns of the electrostatic structure are found to be quite important for fusion application owing to their association with transport barrier formation. It is confirmed, as is shown in several tokamak experiments, that the thermal transport barrier is linked with electrostatic structure through the radial electric field shear that can reduce the fluctuation resulting in anomalous transport. This article describes in detail spatio-temporal evolution during self-sustained oscillation, together with correlation between the radial electric field and other plasma parameters. An experimental survey to find dependence of the temporal and spatial patterns on plasma parameters is performed in order to understand systematically the bifurcation property of the toroidal helical plasma. The experimental results are compared with the neoclassical bifurcation property that is believed to explain the observed bifurcation property of the CHS plasmas. The present results show that the electrostatic property plays an essential role in the structural formation of toroidal helical plasmas, and demonstrate that toroidal plasma is an open system with a strong nonlinearity to provide a new attractive problem to be studied.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.1290483
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
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  • 9
    Online Resource
    Online Resource
    High-performance organic transistors with high- k dielectrics: A comparative study on solution-processed single crystals and vacuum-deposited polycrystalline films of 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene
    AIP Publishing ; 2012
    In:  Applied Physics Letters Vol. 101, No. 22 ( 2012-11-26)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 101, No. 22 ( 2012-11-26)
    Abstract: High carrier-mobility organic field-effect transistors are developed employing high-k gate dielectrics so that unprecedentedly high transconductance is realized. 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b] thiophene (C10-DNTT) solution-crystallized films are coated on hybrid gate insulators of silane self-assembled monolayers and high-k Al2O3 formed by atomic-layer-deposition. Intrinsically high carrier mobility exceeding 10 cm2/Vs in the crystalline C10-DNTT is preserved even on the high-k gate insulators because of suppressed coupling of the field-induced carriers to the polarization of the dielectrics.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.4769436
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 10
    Online Resource
    Online Resource
    Single bunch injection system of the storage ring NIJI-IV for free electron laser use
    AIP Publishing ; 1995
    In:  Review of Scientific Instruments Vol. 66, No. 4 ( 1995-04-01), p. 2796-2800
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 66, No. 4 ( 1995-04-01), p. 2796-2800
    Abstract: The system of single bunch injection (SBI) for the storage ring NIJI-IV was completed. The system was used for the injection of the short pulse beams from an electron gun into only one of the 16 rf buckets in the ring. On a compact storage ring, the multipulse beams in one pulse train can be stored into only one of many bunches by one injection. The optimum number of the grid pulse in one pulse train was determined to improve the storage efficiency and the storage current by one injection. The keeping time of the bump orbit was calculated by using the transfer matrices. The optimum pulse number obtained by the calculation is 2. In the SBI system, the number of grid pulses in one pulse train can be selected by the gate circuit. A snap off diode and a clip line are used to generate 2 ns grid pulses. The measured grid pulse was shorter than the longitudinal space 5.5 ns of the rf bucket with voltage of −80 V. The EIMAC Y-646B cathode-grid assembly is used as the electron source. It is expected that the injection system provides a higher peak current and easier free electron laser use operation in comparison with the rf-knockout system.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1145557
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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