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T. Obiki,
T. Mizuuchi,
H. Okada,
K. Nagasaki,
F. Sano,
S. Kobayashi,
K. Hanatani,
Y. Ijiri,
T. Senju,
K. Yaguchi, [......],
Y. Fukagawa,
S. Nakazawa,
Y. Morita,
S. Nishio,
K. Takahashi,
S. Tsuboi,
M. Yamada,
N. Nishino,
V. Tribaldos,
F. Tabarés
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ABSTRACT: Studies of global energy confinement and toroidal plasma current behaviour for the second harmonic 70 GHz ECH at B = 1–1.5 T are described with emphasis on the magnetic configuration effects in the helical-axis heliotron 'Heliotron J'. At low densities of , the electron temperature reached Te ≈ 1 keV in the core region, indicating the production of collision-less plasmas of electron collisionality ν* 0.1, where ν* = ν/(ve/π R0q). For medium densities of , the preferable energy confinement time, 1.5–2 times larger than that of the ISS95 scaling, was obtained under the condition of localized central heating at B ≈ 1.25 T for the standard configuration of Heliotron J. The measurements of the toroidal current under perpendicular microwave injection revealed the change of the current flow direction as a function of the poloidal magnetic field. The measured current behaviour was found to be qualitatively consistent with that of the bootstrap current predicted from neoclassical theory. The observed flow reversal showed that a proper selection of the field configuration could control the bootstrap current in the helical-axis heliotron. In addition, the current control through the electron cyclotron current drive scenario with oblique injection of microwaves was experimentally examined.
Nuclear Fusion 12/2003; 44(1):47. · 4.09 Impact Factor
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ABSTRACT: The effect of the hyphal wall component (HWC) of Phytophthora infestans on the membrane potentials (Ψm) of cells in the aged cut surface of potato tuber tissue (cv. Rishiri) were investigated. Within a few minutes of the application of HWC (3 mg ml−1), cellular depolarization occurred. Initially, depolarization was rapid. After a mean depolarization of about 25 mV, the Ψm reached an asymptotic plateau. HWC reduced the oxygen dependent electrogenic potential difference (|Ψd|) by about 60%, but exerted little effect on the passive potential difference (|Ψd|). In a later stage, |Ψd| also decreased very gradually. The extent of the HWC effect was not always the same, possibly owing to the heterogeneity of potato cells in their reactivity or accessibility to HWC. There was no difference in the activity on Ψm of HWC isolated from compatible or incompatible races. Results showed that the effect of HWC on the membrane potential of potato cells was different from that of infection by P. infestans.
Physiological Plant Pathology.
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ABSTRACT: As reported previously, penetration of a surface cell of an aged potato slice by an incompatible race of Phytophthora infestans led to depolarization of the diffusion potential component (Ψd) of the membrane potential (Ψ) which began almost simultaneously with penetration. As a result, Ψ was depolarized to nearly −50 mV, then further gradual depolarization occurred until cell death. On the other hand, cell penetration by a compatible race had little effect on Ψd. It is known that cells penetrated by incompatible races die rapidly, whereas those penetrated by compatible races remain alive for several days. Pre-inoculational heat-treatment is known to greatly inhibit the occurrence of hypersensitive cell death, making a resistant host cell susceptible to an otherwise incompatible race. In this study, we examined whether pre-inoculational heat-treatments inhibit the depolarization of Ψd of the cell penetrated by the incompatible race. Treatment of the uninfected aged slice with hot water at 47 °C had no effect on Ψd, and had little if any effect on Ψ and energy-dependent potential (Ψp). When a cell of the pre-inoculationally heat-treated slice was penetrated by the incompatible race, there was no change in its Ψd, Ψ or Ψp. The results indicate that the pre-inoculational heat-treatment inhibited both hypersensitive death and the depolarization of membrane potential which normally occur in response to penetration by incompatible races of P. infestans. The relation between malonate sensitive respiration and the time for hypersensitive cell death is discussed.
Physiological and Molecular Plant Pathology.
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K Nagasaki,
N Yanagi,
H Shidara,
F Sano,
K Kondo,
T Mizuuchi,
H Okada,
M Nakasuga,
S Besshou,
Y Manabe,
W L Ang,
H Kawazome,
S Maeno, K Tomiyama,
H Tsuru,
T Takamiya,
M Takeda,
T Obiki
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ABSTRACT: Electron Bernstein wave heating is studied theoretically and experimentally in heliotron configurations. A ray tracing code for ordinary (O)-extraordinary (X)-electron Bernstein (B) and X-B conversion heating has been developed, in which the three-dimensional magnetic field structure is taken into account. In the O-X-B heating, the deposition condition is strongly Doppler-shifted because of the high parallel refractive index caused by the inhomogeneity of the magnetic field. The slow X-B heating is also possible by launching the slow X-mode from the low field side because of the peculiar magnetic field structure. An effective heating has been observed in the helical-axis heliotron device, Heliotron J, when no electromagnetic resonance exists in the core region. The obtained stored energy is comparable with that in the conventional second harmonic ECH. A possible explanation for this effective heating is presented using the slow X-B mode conversion process.
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T. Mizuuchi,
W.L. Ang,
Y. Nishioka,
T. Kobayashi,
K. Nagasaki,
H. Okada,
K. Kondo,
F. Sano,
S. Besshou,
Y. Nakamura, [......],
S. Maeno,
T. Takamiya,
M. Takeda, K. Tomiyama,
H. Tsuru,
Y. Ohno,
H. Kubo,
H. Yukimoto,
M. Iriguchi,
T. Obiki
[show abstract]
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ABSTRACT: An asymmetric divertor plasma distribution observed in the standard configuration of Heliotron J is reported. The divertor plasma profiles were investigated with two Langmuir probe arrays, which were installed at the geometrically up–down symmetric positions, for three different heating schemes of ECH with 53.2 or 70 GHz microwaves. Although the position of the divertor plasma flux was almost consistent with the footprint position of the divertor field lines, the existence of two types of up–down asymmetry was revealed in the divertor plasma density and floating potential profiles. The first type of asymmetry was mainly observed near the boundary to the ‘private region’. This asymmetry seems to be independent of the heating schemes of the toroidal position of the heating source. As the direction of the confinement field was reversed, the feature of the plasma profile on the top array came to appear on the bottom array, and vice versa. This field-direction dependence indicates that the asymmetric B×∇B drift motion of charged particles might cause this type of asymmetry. The second type of asymmetry was observed in the region away from the boundary and seemed to depend on the heating schemes.
Journal of Nuclear Materials.
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K Ogawa, K. Tomiyama,
Y. Tan,
M. Doan,
Y. Bin,
D. -L. Kwong,
S Yamada,
J. Cole,
Y Katayama,
Hiroshi Mizuta,
S Oda
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T Obiki,
H Okada,
T Mizuuchi,
K Nagasaki,
F Sano,
K Kondo,
M Wakatani,
K Hanatani,
Y Nakamura,
S Besshou, [......],
H Kubo,
Y Nishioka,
Y Ohno,
Y Ijiri,
T Senju,
K Sakamoto,
K Tohshi,
M Shibano,
V Tribaldos,
F Tabarés
[show abstract]
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ABSTRACT: Recent experiments in Heliotron J are reported with special regard to the 53.2-GHz/70-GHz ECH plasma confinement. The energy content of the hydrogen plasma up to ~ 2 kJ has been obtained with 70-GHz, 0.4-MW second harmonic ECH at B = 1.24 T. At low electron densities of (0.2–0.5) ×10 19 m –3 , the collisionless hydrogen plasmas have been successfully produced, which allows us to study the 1/ν electron transport in Heliotron J. The magnetic configuration effects are also studied, showing a sensitive dependence of the attainable energy content on the selected configuration.
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T Obiki,
T Mizuuchi,
K Nagasaki,
H Okada,
F Sano,
K Hanatani,
Y Liu,
T Hamada,
Y Manabe,
H Shidara, [......],
K Kondo,
S Besshou,
Y Nakamura,
M Nakasuga,
M Wakatani,
O Yamagishi,
K Aizawa,
Y Kawazome,
S Maeno, K Tomiyama
[show abstract]
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ABSTRACT: Results obtained in the initial experimental phase of Heliotron J are reported. Electron beam mapping of the magnetic surfaces at a reduced DC magnetic field has revealed that the observed surfaces are in basic agreement with the ones calculated on the basis of the measured ambient field around the device. For 53.2 GHz second harmonic ECH hydrogen plasmas, a fairly wide resonance range for breakdown and heating by the TE02 mode has been observed in Heliotron J as compared with that in Heliotron E. With ECH injection powers up to ≈400 kW, diamagnetic stored energies up to ≈0.7 kJ were obtained without optimized density control.
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ABSTRACT: In this article we describe a diamagnetic double-loop method for measurement of the energy stored in a magnetized plasma. Two concentric diamagnetic loops enclose a plasma column. The advantage of this method is the capability to eliminate to a high extent the background magnetic field and the effect of eddy currents in the measurement of relatively small diamagnetic signals. This method was applied to initial plasmas produced in the helical axis stellarator Heliotron J. A stored energy of 0.7 kJ was measured with a resolution of 0.02 kJ at rippling magnetic field of 1 T in a plasma heated by rf discharges up to 400 kW. This diamagnetic double-loop method improved the signal to noise ratio of the conventional single loop method sixfold. The magnetic diagnostics hardware, experimental results, and an error estimate are presented. © 2001 American Institute of Physics.
