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  • AIP Publishing  (7,142)
  • 1995-1999  (7,142)
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  • AIP Publishing  (7,142)
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  • 1995-1999  (7,142)
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  • 1
    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
    detail.hit.zdb_id: 1472746-8
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  • 2
    Online Resource
    Online Resource
    Review of deuterium–tritium results from the Tokamak Fusion Test Reactor
    AIP Publishing ; 1995
    In:  Physics of Plasmas Vol. 2, No. 6 ( 1995-06-01), p. 2176-2188
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 2, No. 6 ( 1995-06-01), p. 2176-2188
    Abstract: After many years of fusion research, the conditions needed for a D–T fusion reactor have been approached on the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. For the first time the unique phenomena present in a D–T plasma are now being studied in a laboratory plasma. The first magnetic fusion experiments to study plasmas using nearly equal concentrations of deuterium and tritium have been carried out on TFTR. At present the maximum fusion power of 10.7 MW, using 39.5 MW of neutral-beam heating, in a supershot discharge and 6.7 MW in a high-βp discharge following a current rampdown. The fusion power density in a core of the plasma is ≊2.8 MW m−3, exceeding that expected in the International Thermonuclear Experimental Reactor (ITER) [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239] at 1500 MW total fusion power. The energy confinement time, τE, is observed to increase in D–T, relative to D plasmas, by 20% and the ni(0) Ti(0) τE product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity in both supershot and limiter-H-mode discharges. Extensive lithium pellet injection increased the confinement time to 0.27 s and enabled higher current operation in both supershot and high-βp discharges. Ion cyclotron range of frequencies (ICRF) heating of a D–T plasma, using the second harmonic of tritium, has been demonstrated. First measurements of the confined alpha particles have been performed and found to be in good agreement with TRANSP [Nucl. Fusion 34, 1247 (1994)] simulations. Initial measurements of the alpha ash profile have been compared with simulations using particle transport coefficients from He gas puffing experiments. The loss of alpha particles to a detector at the bottom of the vessel is well described by the first-orbit loss mechanism. No loss due to alpha-particle-driven instabilities has yet been observed. D–T experiments on TFTR will continue to explore the assumptions of the ITER design and to examine some of the physics issues associated with an advanced tokamak reactor.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.871303
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
    detail.hit.zdb_id: 1472746-8
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  • 3
    Online Resource
    Online Resource
    Deuterium–tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor
    AIP Publishing ; 1997
    In:  Physics of Plasmas Vol. 4, No. 5 ( 1997-05-01), p. 1714-1724
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 4, No. 5 ( 1997-05-01), p. 1714-1724
    Abstract: Experiments in the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 2, 2176 (1995)] have explored several novel regimes of improved tokamak confinement in deuterium–tritium (D–T) plasmas, including plasmas with reduced or reversed magnetic shear in the core and high-current plasmas with increased shear in the outer region (high li). New techniques have also been developed to enhance the confinement in these regimes by modifying the plasma-limiter interaction through in situ deposition of lithium. In reversed-shear plasmas, transitions to enhanced confinement have been observed at plasma currents up to 2.2 MA (qa≈4.3), accompanied by the formation of internal transport barriers, where large radial gradients develop in the temperature and density profiles. Experiments have been performed to elucidate the mechanism of the barrier formation and its relationship with the magnetic configuration and with the heating characteristics. The increased stability of high-current, high-li plasmas produced by rapid expansion of the minor cross section, coupled with improvement in the confinement by lithium deposition has enabled the achievement of high fusion power, up to 8.7 MW, with D–T neutral beam heating. The physics of fusion alpha-particle confinement has been investigated in these regimes, including the interactions of the alphas with endogenous plasma instabilities and externally applied waves in the ion cyclotron range of frequencies. In D–T plasmas with q0 & gt;1 and weak magnetic shear in the central region, a toroidal Alfvén eigenmode instability driven purely by the alpha particles has been observed for the first time. The interactions of energetic ions with ion Bernstein waves produced by mode conversion from fast waves in mixed-species plasmas have been studied as a possible mechanism for transferring the energy of the alphas to fuel ions.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.872274
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1997
    detail.hit.zdb_id: 1472746-8
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  • 4
    Online Resource
    Online Resource
    Improvement of a 500 keV heavy-ion-beam probe for JIPP T-IIU tokamak
    AIP Publishing ; 1995
    In:  Review of Scientific Instruments Vol. 66, No. 1 ( 1995-01-01), p. 321-323
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 66, No. 1 ( 1995-01-01), p. 321-323
    Abstract: Several improvements in the high-voltage heavy-ion-beam probe (HIBP) are discussed. (1) It is clearly found that the precision slide mount of the detector plates 30° parallel to the base electrode is very effective for the determination of the in-plane entrance angle of the beam in the analyzer to estimate the error in the potential measurement. (2) A two-staged optical trap in the HIBP greatly reduced the effect of the UV radiation in the analyzer. (3) A multiple-plate detector up to 13 measurement points clearly showed the direction of the propagation of the turbulence and path-integral effects.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1146399
    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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  • 5
    Online Resource
    Online Resource
    Fusion plasma experiments on TFTR: A 20 year retrospective
    AIP Publishing ; 1998
    In:  Physics of Plasmas Vol. 5, No. 5 ( 1998-05-01), p. 1577-1589
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 5, No. 5 ( 1998-05-01), p. 1577-1589
    Abstract: The Tokamak Fusion Test Reactor (TFTR) (R. J. Hawryluk, to be published in Rev. Mod. Phys.) experiments on high-temperature plasmas, that culminated in the study of deuterium–tritium D–T plasmas containing significant populations of energetic alpha particles, spanned over two decades from conception to completion. During the design of TFTR, the key physics issues were magnetohydrodynamic (MHD) equilibrium and stability, plasma energy transport, impurity effects, and plasma reactivity. Energetic particle physics was given less attention during this phase because, in part, of the necessity to address the issues that would create the conditions for the study of energetic particles and also the lack of diagnostics to study the energetic particles in detail. The worldwide tokamak program including the contributions from TFTR made substantial progress during the past two decades in addressing the fundamental issues affecting the performance of high-temperature plasmas and the behavior of energetic particles. The progress has been the result of the construction of new facilities, which enabled the production of high-temperature well-confined plasmas, development of sophisticated diagnostic techniques to study both the background plasma and the resulting energetic fusion products, and computational techniques to both interpret the experimental results and to predict the outcome of experiments.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.872825
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1998
    detail.hit.zdb_id: 1472746-8
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  • 6
    Online Resource
    Online Resource
    A rotating coil probe for the magnetic field measurement on a long pulsed tokamak
    AIP Publishing ; 1999
    In:  Review of Scientific Instruments Vol. 70, No. 1 ( 1999-01-01), p. 445-448
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 70, No. 1 ( 1999-01-01), p. 445-448
    Abstract: In order to determine the magnitude and the position of the plasma current in a long pulsed tokamak such as the International Thermonuclear Experimental Reactor (ITER), it is urged to establish a reliable method which is free from the zero-level drift of the integrator as well as the radiation damage for the steady-state magnetic field measurement. For this purpose, we have developed a hybrid system, a combination of a conventional magnetic probe for the measurement of fast varying magnetic field and a rotating coil magnetic probe for that of slowly varying field. The rotating coil is energized by an air turbine to avoid electromagnetic interference and the induce signal with a constant rotation frequency is picked up through a transformer to eliminate mechanical contacts. An automatic gain control circuit is also designed for the compensation of rotation speed fluctuation. The system is proved to achieve a flat frequency response with a proper choice of cross over frequency for high- and low-frequency systems. The rotating coil probe is tested for over 170 h without any trouble. The probe was applied to the poloidal magnetic field measurement on the TRIAM-1M long pulsed tokamak, and proved to work satisfactorily.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1149281
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1999
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 7
    Online Resource
    Online Resource
    Continuum x-ray source as a calibration system for charge coupled devices
    AIP Publishing ; 1998
    In:  Review of Scientific Instruments Vol. 69, No. 2 ( 1998-02-01), p. 392-395
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 69, No. 2 ( 1998-02-01), p. 392-395
    Abstract: We present x-ray spectra obtained by a charge coupled device (CCD) from an electron impacting x-ray source using several kinds of electron targets: Au, Al–bronze, Al, and pure Al. The x rays from the source are dispersed by a grating and the dispersed x rays are focused on the CCD. Owing to the fine spatial and moderate energy resolutions of the CCD, fine spectra with 2 eV energy resolution up to 2.2 keV are obtained. X rays from the pure Al target (99.999% purity) provide good continuum x rays except for Al K x rays. This continuum source is useful as a calibration source for low energy x-ray detectors.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1148671
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1998
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 8
    Online Resource
    Online Resource
    Initial long-pulse plasma heating at reduced power with negative-ion-based neutral beam injector in large helical device
    AIP Publishing ; 1999
    In:  Review of Scientific Instruments Vol. 70, No. 11 ( 1999-11-01), p. 4260-4265
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 70, No. 11 ( 1999-11-01), p. 4260-4265
    Abstract: We have achieved long-pulse plasma heating using a negative-ion-based neutral beam injector (NBI) in the large helical device (LHD), where the confinement magnetic field is generated by only external superconducting coils. In the initial long-pulse experiments at lower power than that in short-pulse experiments, 80 keV–1.1 MW NBI heating lasted for 10 s with a little increase in the plasma density at the pulse end. Almost steady-state plasma heating was achieved for 21 s with 66 keV–0.6 MW NB injection. Plasma relaxation oscillation phenomena at a period of 1–2 s were also observed for 20 s. Above 1 keV plasma was easily sustained with a long-pulse NBI heating in LHD, without the current drive nor the disruption in tokamaks. Negative ion source operation was stable and the cooling water temperature rise of beam accelerator grids was nearly saturated with a temperature rise below 10 °C. For a higher power injection, the pulse duration is determined by the beam blocking, where the reionization loss is exponentially increased together with an increase in outgas in the injection port. The port conditioning by a careful repetition of injection is effective to the extension of the injection duration and the plasma maintenance duration. The initial long-pulse NBI heating at the reduced power has demonstrated an ability of steady-state operation in superconducting LHD.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1150063
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1999
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 9
    Online Resource
    Online Resource
    Development of millimeter-wave two-dimensional imaging array
    AIP Publishing ; 1999
    In:  Review of Scientific Instruments Vol. 70, No. 1 ( 1999-01-01), p. 1003-1006
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 70, No. 1 ( 1999-01-01), p. 1003-1006
    Abstract: A millimeter-wave two-dimensional imaging array has been developed for diagnostics of magnetically confined plasmas. It is applied to the plug cell of the GAMMA 10 tandem mirror, and measures time evolution of radial and axial line-density and electron cyclotron emission (ECE) profiles in one plasma shot. The monolithic-type GaAs Schottky diode detector having an antenna and built-in amplifier on a GaAs substrate is newly fabricated using monolithic microwave integrated circuit (MMIC) technology. This novel detector is developed to attain high frequency response up to submillimeter-wave region and wideband heterodyne characteristics, and is expected to be applied to ECE imaging in a large helical device. The response of the detector is compared with that of the hybrid-type detector using beam-lead Schottky barrier diodes. The first experimental result of the ECE measurement is reported using a heterodyne radiometer with the MMIC detector.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1149424
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1999
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 10
    Online Resource
    Online Resource
    Drift-wave-like density fluctuations in the Advanced Toroidal Facility (ATF) torsatron
    AIP Publishing ; 1995
    In:  Physics of Plasmas Vol. 2, No. 2 ( 1995-02-01), p. 398-413
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 2, No. 2 ( 1995-02-01), p. 398-413
    Abstract: Density fluctuations in low-collisionality, low-beta (β∼0.1%), currentless plasmas produced with electron cyclotron heating (ECH) in the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] have been studied using a 2 mm microwave scattering diagnostic. Pulsed gas puffing is used to produce transient steepening of the density profile from its typically flat shape; this leads to growth in the density fluctuations when the temperature and density gradients both point in the same direction in the confinement region. The wave number spectra of the fluctuations that appear during this perturbation have a maximum at higher k⊥ρs (∼1) than is typically seen in tokamaks. The in–out asymmetry of the fluctuations along the major radius correlates with the distribution of confined trapped particles expected for the ATF magnetic field geometry. During the perturbation, the relative level of the density fluctuations in the confinement region (integrated over normalized minor radii ρ from 0.5 to 0.85) increases from ñ/n∼1% when the density profile is flat to ñ/n∼3% when the density profile is steepened. These observations are in qualitative agreement with theoretical expectations for helical dissipative trapped-electron modes (DTEMs), which are drift-wave instabilities associated with particle trapping in the helical stellarator field; they suggest that trapped-electron instabilities may play a role in constraining the shape of the density profile in ATF, but have little effect on global energy confinement.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.870966
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
    detail.hit.zdb_id: 1472746-8
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