Faculty Profiles - OHNO, Noriyasu

Papers - OHNO, Noriyasu

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Validity of Electron Temperature Measurement by Using Boltzmann Plot Method in Radio Freauency Inductive Discharge in the Atmospheric Pressure Range Reviewed

N.Ohno, M.Razzak, H.Ukai, S.Takamura, Y.Uesugi

Plasma Fusion Res. Vol. 1 page： 028(9pages) 2006

Fast Initiation and Mode Transition of Radio Frequency Induction Plasmas at Atmospheric Pressure Using Tungsten Pin Electrodes Array Reviewed International journal

RAZZAK M. Abdur, TAKAMURA Shuichi, OHNO Noriyasu

Plasma and Fusion Research ( 1 ) page： 6 - 6 2006

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：社団法人プラズマ・核融合学会

The effects of using an array of tungsten pin electrodes on the ignition dynamics of radio frequency (rf) discharges generated by inductively coupled plasma (ICP) technique at atmospheric pressure are investigated experimentally. The experimental observations reveal that the array of tungsten pin electrodes successfully enhance the initial discharges maintained by the strong electrostatic field with stable and fast ignition, which enables us to sustain efficient rf induction plasmas at atmospheric pressure range.

DOI： 10.1585/pfr.1.006

Validity of Electron Temperature Measurement by Using Boltzmann Plot Method in Radio Frequency Inductive Discharge in the Atmospheric Pressure Range Reviewed International journal

OHNO Noriyasu, RAZZAK M. Abdur, UKAI Hiroshi, TAKAMURA Shuichi, UESUGI Yoshihiko

Plasma and Fusion Research ( 1 ) page： 28 - 28 2006

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：社団法人プラズマ・核融合学会

The validity of electron temperature measurement using the Boltzmann plot method was investigated in a radio frequency (rf) inductive discharge in the atmospheric pressure range. Since the Boltzmann plot method requires local thermal equilibrium (LTE), the parameter regions of electron temperature and electron density, in which the Boltzmann plot method is applicable, were analyzed in terms of a comparison of the spontaneous emission and collisional excitation to the excited states. It is observed that in our rf-inductive plasma near the atmospheric pressure range the Boltzmann plot method does not provide an exact measurement of electron temperature because of relatively low electron density, which does not satisfy the calculation criteria. An alternative method employing a combination of the Stark broadening measurement and the Saha-Boltzmann equation was demonstrated to more accurately determine the plasma parameters (electron temperature and electron density).

DOI： 10.1585/pfr.1.028

Design of a novel T-lclimmittance conversion circuit for dynamic and non-linear loads Reviewed International coauthorship International journal

Razzak M.A., Takamura S., Ohno N., Uesugi Y.

Proceedings of 4th International Conference on Electrical and Computer Engineering, ICECE 2006 page： 13 - 16 2006

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Proceedings of 4th International Conference on Electrical and Computer Engineering, ICECE 2006

In recent years, the immittance conversion topology [1] has become attractive as a novel power conversion strategy because of its features that a constant voltage source is converted to a constant current source and vice versa. However, the design of an ideal immittance circuit in the high-power (∼kW) and high-frequency (∼MHz) range is practically very important, especially when apply to a dynamic and non-linear load such as induction plasma. In this article, the design and development of an ideal T-LCL immittance circuit is reported. The performance of the designed immittance circuit is analysed by using a time-varying inductive plasma load.

DOI： 10.1109/ICECE.2006.355278

Scopus

Optimum generation of high heat flux toroidal plasmas by RF ohmic discharge Reviewed International journal

Masuda H., Kitahara H., Nagase M., Ohno N., Takamura S., Takagi M.

32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets - Europhysics Conference Abstracts Vol. 3 page： 1946 - 1949 2005.12

Language：English Publishing type：Research paper (international conference proceedings) Publisher：32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets - Europhysics Conference Abstracts

We have developed a new toroidal divertor plasma simulator, NAGDIS-T (NAGoya DIvertor plasma Simulator with Toroidal magnetic configuration). Plasma is generated by RF Joule discharge. In order to obtain high density plasmas relevant to divertor plasmas in fusion devices, we investigate the optimum condition of RF Joule discharge by varying gas pressure and driving frequency. The experimental result shows that the optimum condition strongly depends on these parameters. Copyright © (2005) by the European Physical Society (EPS).

Scopus

High-Z Dust Generation on Tungsten Surfaces due to Synergetic Erosion of Deuterium/Helium Plasma Exposures Reviewed

西島大, 天野浩嗣, 大野哲靖, 吉田直亮, 高村秀一

プラズマ・核融合学会誌 = Journal of plasma and fusion research Vol. 81 ( 9 ) page： 703 - 707 2005.9

Language：English Publishing type：Research paper (scientific journal) Publisher：社団法人プラズマ・核融合学会

Low-energy and high-flux plasma exposures on tungsten surfaces result in blister/hole formation. Subsequent He plasma exposure at 2,000 K on the blister-rich surface forms a hole structure on the surface, including the blister surface, and some blisters collapse due to recrystallization and bubble formation on the blister skin. Grain ejections were observed after deuterium plasma exposure at 550 K on a W surface on which a hole structure had formed due to He pre-exposure at 1,600 K.

DOI： 10.1585/jspf.81.703

Efficient Radio Frequency Inductive Discharges in Near Atmospheric Pressure Using Immittance Conversion Topology Reviewed

Razzak M. Abdur, 高村秀一, 上杉喜彦, 大野哲靖

プラズマ・核融合学会誌 = Journal of plasma and fusion research Vol. 81 ( 3 ) page： 204 - 211 2005.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：社団法人プラズマ・核融合学会

A radio frequency (rf) inductive discharge in atmospheric pressure range requires high voltage in the initial startup phase and high power during the steady state sustainment phase. It is, therefore, necessary to inject high rf power into the plasma ensuring the maximum use of the power source, especially where the rf power is limited. In order to inject the maximum possible rf power into the plasma with a moderate rf power source of few kilowatts range, we employ the immittance conversion topology by converting a constant voltage source into a constant current source to generate efficient rf discharge by inductively coupled plasma (ICP) technique at a gas pressure with up to one atmosphere in argon. A novel T-LCL immittance circuit is designed for constant-current high-power operation, which is practically very important in the high-frequency range, to provide high effective rf power to the plasma. The immittance conversion system combines the static induction transistor (SIT)-based radio frequency (rf) high-power inverter circuit and the immittance conversion elements including the rf induction coil. The basic properties of the immittance circuit are studied by numerical analysis and verified the results by experimental measurements with the inductive plasma as a load at a relatively high rf power of about 4 kW. The performances of the immittance circuit are also evaluated and compared with that of the conventional series resonance circuit in high-pressure induction plasma generation. The experimental results reveal that the immittance conversion circuit confirms injecting higher effective rf power into the plasma as much as three times than that of the series resonance circuit under the same operating conditions and same dc supply voltage to the inverter, thereby enhancing the plasma heating efficiency to generate efficient rf inductive discharges.

DOI： 10.1585/jspf.81.204

Characteristic changes of deuterium retention on tungsten surfaces due to low-energy helium plasma pre-exposure Reviewed

Nishijima D, Sugimoto T, Iwakiri H, Ye MY, Ohno N, Yoshida N, Takamura S

JOURNAL OF NUCLEAR MATERIALS Vol. 337 ( 1-3 ) page： 927 - 931 2005.3

Hydrogen Blister Formation on Cold-Worked Tungsten with Layered Structure Reviewed

D.Nishijima, T.Sugimoto, M.Ye, N.Ohno, S.Takamura

Jpn. J. Appl. Phys. Vol. 44 ( 1A ) page： 380-382 2005

Overview of JT-60U progress towards steady-state advanced tokamak Reviewed

S.Ide, N.Ohno, JT-60U Team

Nuclear Fusion Vol. 45 page： S48-S62 2005

Micron-Bubble Formation on Polycrystal Tungsten due to Low-Energy and high-Flux Helium Plasma Exposure Reviewed

D.Nishijima, M.Miyamoto, H.Iwakiri, M.Ye, N.Ohno, K.Tokunaga, N.Yoshida, S.Takamura

Nuclear Fusion Vol. 46 page： 561-564 2005

Further Roughing of Tungsten Surface due to Transient Heat Load by Laser Irradiation during Helium Plasma Exposure Reviewed

S.Kajita, D.Nishijima, N.Ohno, S.Takamura

J. Plasma Fusion Res. Vol. 81 page： 745-746 2005

High-Z Dust Generation on Tungsten Surface due to Synergetic Erosion of Deuterium/Helium Plasma Exposure Reviewed

D.Nishijima, K.Amano, N.Ohno, N.Yoshida, S.Takamura

J. Plasma Fusion Res. Vol. 81 page： 703-707 2005

Suppression of Blister Formation and Deuterium Retention on Tungsten Surface due to Mechanical Polishing and Helium Pre-exposure Reviewed

D.Nishijima, H.Iwakiri, K.Amano, M.Y.Ye, N.Ohno, K.Tokunaga, N.Yoshida, S.Takamura

Nucl. Fusion Vol. 45 page： 669-674 2005

Efficient Radio Frequency Inductive Discharge in Hear Atmospheric Pressure Using Imittance Conversion Topology Reviewed

M.A.Razzak, S.Takamura, Y.Uesugi, N.Ohno

J. Plasma Fusion Res. Vol. 81 ( 3 ) page： 204-211 2005

Characterstic changes of deuterium rentention on tungsten surfaces due to low-energy helium plasma pre-exposure Reviewed

D.Nishijima, T.Sugimoto, H.Iwakiri, M.Y.Ye, N.Ohno, N.Yoshida, S.Takamura

Journal of Nuclear Materials Vol. 337-339 page： 927-931 2005

Carbon dust formation from re-deposited layers in high-density hydrogen/helium plasmas in the NAGDIS-II device Reviewed

N.Ohno, Y.Kobayashi, T.Sugimoto, S.Takamura

Journal of Nuclear Materials Vol. 337-339 page： 35-39 2005

Neutral helium line emission for edge plasma conditions Reviewed

F.B.Rosmej, R.Stamm, S.Fritzsche, H.Capes, M.Koubiti, Y.Marandet, V.S.Lisitsa, N.Ohno, S.Takamura, D.Nishijima

Journal of Nuclear Materials Vol. 337-339 page： 1101-1105 2005

Formation mechanism of bubbles and holes on tungsten surface with low-energy and high-flux helium plasma irradiation in NAGDIS-II Reviewed

Dai. Nishijima, M.Y.Ye, N.Ohno, S.Takamura

J. Nucl. Mater. Vol. 329-333 page： 1029-1033 2005

Transition from electrostatic-to-electromagnetic mode in a radio-frequency Ar inductively coupled plasma in atmospheric pressure Reviewed International journal

Razzak MA, Kondo K, Uesugi Y, Ohno N, Takamura S

JOURNAL OF APPLIED PHYSICS Vol. 95 ( 2 ) page： 427 - 433 2004.1

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Papers - OHNO, Noriyasu