摘要 :
Progress in the integrated development of the helical system in the Large Helical Device (LHD) is described in this paper. Understanding of net current-free plasmas has been deepened in the extended operational regime. Geometrical...
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Progress in the integrated development of the helical system in the Large Helical Device (LHD) is described in this paper. Understanding of net current-free plasmas has been deepened in the extended operational regime. Geometrical optimization based on neoclassical theory has revealed that good confinement, equivalent to the tokamak H-mode, can be obtained in the collisionless regime. This approach has also demonstrated that anomalous transport is reduced simultaneously, which poses a working hypothesis that optimization of neoclassical transport suppresses turbulent anomalous transport as well. With regard to the magnetohydrodynamic instability, LHD has discovered that interchange instability is benign in
the magnetic hill. These two findings have produced a synergistic effect on the enhancement of confinement and plasma β. Remarkable proof of the advantage of helical systems can be seen in very high density operation, which is not accessible in tokamaks. Abundant integrated knowledge about three-dimensional physics has been extracted from these achievements. This progress is important in the assessment of the potential of a helical fusion reactor and makes a significant complementary contribution to tokamaks as well.
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摘要 :
Since the foundation of National Institute for Fusion Science (NIFS) in 1989, the primary mission of the applied superconductivity and cryogenic researches has been focused on the development of the large helical device (LHD): the...
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Since the foundation of National Institute for Fusion Science (NIFS) in 1989, the primary mission of the applied superconductivity and cryogenic researches has been focused on the development of the large helical device (LHD): the largest fusion experimental apparatus exclusively utilizing superconducting technologies. The applied superconductivity and cryogenics group in NIFS was organized to be responsible for this activity. As a result of extensive research activities, the construction of LHD was completed in 1997. Since then, the LHD superconducting system has been demonstrating high availability of more than 97% during eight years operation and it keeps proving high reliability of large-scale superconducting systems. This paper describes the extensive activities of the applied superconductivity and cryogenic researches in NIFS during and after the development of LHD and the fundamental researches that aim at realizing a helical-type fusion reactor.
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摘要 :
The Large Helical Device (LHD) is a heliotron-type device employing large-scale superconducting magnets to enable advanced studies of net-current-free plasmas. The major goal of the LHD experiment is to demonstrate the high perfor...
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The Large Helical Device (LHD) is a heliotron-type device employing large-scale superconducting magnets to enable advanced studies of net-current-free plasmas. The major goal of the LHD experiment is to demonstrate the high performance of helical plasmas in a reactor-relevant plasma regime. Engineering achievements and operational experience greatly contribute to the technological basis for a fusion energy reactor. Thorough exploration for scientific and systematic understanding of the physics in the LHD is an important step to a helical fusion reactor. In the 12 years since the initial operation, the physics database as well as operational experience has been accumulated, and the advantages of stable and steady-state features have been demonstrated by the combination of advanced engineering and the intrinsic phys-
ical advantages of helical systems in the LHD. The cryogenic system has been operated for 56000 h in total without any serious trouble and routinely provides a confining magnetic field up to 2.96 T in steady state. The heating capability to date is 23 MW of neutral beam injection, 3 MW of ion cyclotron resonance frequency, and 2.5 MW of electron cyclotron resonance heating. Highlighted physical achievements are high beta (5.1 %), high density (1.2 × 10~(21) m~(-3)), and steady-state operation (3200 s with 490 kW).
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The Large Helical Device (LHD) is one of the world's largest superconducting systems. It consists of a pair of pool-cooled helical coils, three pairs of forced-flow -cooled poloidal coils, nine superconducting bus lines, a helium ...
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The Large Helical Device (LHD) is one of the world's largest superconducting systems. It consists of a pair of pool-cooled helical coils, three pairs of forced-flow -cooled poloidal coils, nine superconducting bus lines, a helium liquefier and refrigerator of 10-kW class, and six dc power supplies. Its stored magnetic energy reaches 0.8 GJ. Availability higher than 99% has been achieved in the long-term continuous operation since the first cool-down in February 1998 owing to the robustness of the systems and to efforts of maintenance and operation. One major problem is shortage of cryogenic stability of the helical coil conductor due to the slow current diffusion into a thick pure aluminum stabilizer. To improve its
cryogenic stability by lowering the temperature, a sub-cooling system was installed before the tenth cooldown. The outlet temperature of the coil was successfully lowered to 3.8 K from 4.4 K of the saturated temperature, and its operation current was increased to 11.6 kA from 11.0 kA. These experiences of modification, maintenance, and operation should be useful for next large superconducting systems.
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摘要 :
Performance of the superconducting helical coils of the Large Helical Device (LHD) during the past 12 cooling cycles is reviewed. The pair of helical coils are pool cooled by liquid helium and wound with aluminum-stabilized NbTi/C...
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Performance of the superconducting helical coils of the Large Helical Device (LHD) during the past 12 cooling cycles is reviewed. The pair of helical coils are pool cooled by liquid helium and wound with aluminum-stabilized NbTi/Cu composite-type superconductors. Intensive efforts have been made to reliably carry out excitations, as more than 20 temporary normal transitions were observed. It was found that the minimum propagation current was about 10% lower than the nominal operation current. To improve the cryogenic stability, subcooled liquid helium has been supplied since 2006 using cold compressors, and the inlet temperature is lowered to be 3.2 K. The toroidal magnetic field has been
raised by 5% and the plasma parameters are being enhanced. Pulse-height analysis is successfully applied on the balance voltage and acoustic emission signals to investigate the mechanical properties of the windings and their changes in years of operation. Short-duration normal transitions are automatically detected using a sophisticated monitoring system and careful operations are continued.
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The large helical device is a heliotron device with L = 2 and M= 10 continuous helical coils and three pairs of poloidal coils, and all of coils are superconductive. Since the experiments started in 1998, the development of engine...
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The large helical device is a heliotron device with L = 2 and M= 10 continuous helical coils and three pairs of poloidal coils, and all of coils are superconductive. Since the experiments started in 1998, the development of engineering technologies and the demonstration of large-superconducting-machine operations have greatly contributed to an understanding of physics in currentless plasmas and a verification of the capability of fully steady-state operation. In recent plasma experiments, the steady state and high-beta experiments, which are the most important subjects for the realization of attractive fusion reactors, have progressed remarkably and produced two world-record parameters, i.e. the highest average beta of 4.5% in helical devices and the highest total input energy of 1.6 GJ in all magnetic confinement devices. No degradation has been observed in the coil performance, and stable cryogenic operational schemes at 4.4 K have been established. The physics and engineering results from the LHD experiment directly contribute to the design study for a D-T fusion demo reactor FFHR with a LHD-type heliotron configuration.
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An overview of conceptual design activities on the LHD-type helical reactor FFHR is presented, mainly focusing on optimization studies on the reactor size and the proposal of a long-life blanket. A major radius of around 15 m is t...
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An overview of conceptual design activities on the LHD-type helical reactor FFHR is presented, mainly focusing on optimization studies on the reactor size and the proposal of a long-life blanket. A major radius of around 15 m is the present candidate under the constraints of the energy confinement achieved in LHD, a maximum magnetic field around 13 T with a current density around 30 A/mm~2 and a neutron wall loading around 1.5 MW/m~2. R&D on super-conducting magnet systems of large scale, high field and high current-density are new challenging targets based on the LHD. The development of new design tools has been started aiming at establishing a virtual power plant (VPP) and a virtual reality system for 3D design assisting. Next design issues are mainly on engineering optimization of the first wall thickness, the detailed 3D blanket system, and unscheduled replacements of breeder blankets.
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摘要 :
Based on high-density and high-temperature plasma experiments in the large helical device (LHD), conceptual design studies of the LHD-type helical DEMO reactor FFHR-d1 have been conducted by integrating wide-ranged R&D activities on core plasmas and reactor technologies through cooperative researches under the fusion engineering research project, which has been launched newly in NIFS. Current activities for the FFHR-dl in this project are presented on design window analyses with designs on core plasma, neutronics for liquid blankets, continuous helical magnets, pellet fueling, tritium systems and plasma heating devices....
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Based on high-density and high-temperature plasma experiments in the large helical device (LHD), conceptual design studies of the LHD-type helical DEMO reactor FFHR-d1 have been conducted by integrating wide-ranged R&D activities on core plasmas and reactor technologies through cooperative researches under the fusion engineering research project, which has been launched newly in NIFS. Current activities for the FFHR-dl in this project are presented on design window analyses with designs on core plasma, neutronics for liquid blankets, continuous helical magnets, pellet fueling, tritium systems and plasma heating devices.
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Based on the recent experimental results of the LHD and the magnet technology-cost basis developed for the ITER construction, the design windows of helical reactors are analysed. For searching design windows and investigating thei...
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Based on the recent experimental results of the LHD and the magnet technology-cost basis developed for the ITER construction, the design windows of helical reactors are analysed. For searching design windows and investigating their economical potential, we have developed a mass-cost estimating model linked with the system design code (HeliCos). We found that the LHD-type helical reactor has the technically and economically attractive design windows, where the major radius is increased as large as for the sufficient blanket space, but the magnetic stored energy is decreased to a reasonable level because of lower magnetic field with the convenient physics basis of the H factor near 1.1 to the ISS04 scaling and beta value of 5%.
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This article reviews 10 years of engineering and physics achievements by the Large Helical Device (LHD) project with emphasis on the latest results. The LHD is the largest magnetic confinement device among diversified helical syst...
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This article reviews 10 years of engineering and physics achievements by the Large Helical Device (LHD) project with emphasis on the latest results. The LHD is the largest magnetic confinement device among diversified helical systems and employs the world's largest superconducting coils. The cryogenic system has been operated for 50,000 h in total without any serious trouble and routinely provides a confining magnetic field up to 2.96T in steady state. The heating capability to date is 23 MW of NBI, 2.9 MW of ICRF and 2.1 MW of ECH. Negative-ion-based ion sources with the accelerating voltage of 180 keV are used for a tangential NBI with the power of 16 MW. The ICRF system has full steady-state operational capability with 1.6 MW. In these 10 years, operational experience as well as a physics database have been accumulated and the advantages of stable and steady-state features have been demonstrated by the combination of advanced engineering and the intrinsic physical advantage of helical systems in LHD. Highlighted physical achievements are high beta (5% at the magnetic field of0.425T), high density (1.1 × 10~(21) m~(-3) at the central temperature of 0.4keV), high ion temperature (T_i of 5.2 keV at 1.5 × 10~(19) m~(-3)), and steady-state operation (3200 s with 490 kW). These physical parameters have elucidated the potential of net-current free helical plasmas for an attractive fusion reactor. It also should be pointed out that a major part of these engineering and physics achievements is complementary to the tokamak approach and even contributes directly to ITER.
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