O. Fukumasa

Publications (15)2.7 Total impact

• Article: Hydrogen atomic pair-ion production on catalyst surface.

  W Oohara, O Fukumasa
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  ABSTRACT: To generate a hydrogen pair-ion plasma consisting of only hydrogen atomic pair ions, i.e., H(+) and H(-) ions, the efficient production of pair ions is required. When discharged hydrogen plasma is irradiated to a Ni catalyst, pair ions are produced on the catalyst surface. It is clarified that hydrogen chemisorption on the catalyst affects pair-ion production.
  The Review of scientific instruments 02/2010; 81(2):023507. · 1.52 Impact Factor
• Article: Enhancement of D{sup -} Negative Ion Volume Production in Pure Deuterium Plasmas

  O. Fukumasa, T. Nakano, S. Mori, W. Oohara, K. Tsumori, Y. Takeiri
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  ABSTRACT: Pure volume production of D{sup -} negative ions is studied in rectangular negative ion source equipped with an external magnetic filter (MF). Plasma parameters (n{sub e} and T{sub e}) in D{sub 2} plasmas are varied mainly in the downstream region by changing the magnetic field intensity of the MF (i.e., B{sub MF}). Production and control of D{sub 2} plasma is nearly the same as that of H{sub 2} plasmas, although the values of n{sub e} and T{sub e} in D{sub 2} plasma are slightly higher than that of H{sub 2} plasmas in both the source and the extraction regions. On D{sup -}/H{sup -} production, however, it appears some different points. By varying the B{sub MF}, H{sup -} production in the extraction region is remarkably changed corresponding to the variation of n{sub e} and T{sub e} in the extraction region. On the other hand, D{sup -} production is not so varied under the same discharge conditions in H{sub 2} plasmas. This difference in D{sup -} production is not well explained only variation of n{sub e} and T{sub e} in D{sub 2} plasmas. Optimum B{sub MF} and gas pressure for D{sup -} production is slightly higher than that for H{sup -} production.
  AIP Conference Proceedings 03/2009; 1097(1).
• Source

  Available from: yamaguchi-u.ac.jp

  Article: Modeling of negative ion production in hydrogen plasmas

  O. Fukumasa
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  ABSTRACT: Effects of cesium vapor injection on H^- production in a tandem volume source are studied numerically as a function of plasma parameters. Model calculation is performed by solving a set of particle balance equations for steady-state hydrogen discharge plasmas. The results with a focus on electron temperature and gas pressure dependence on H^- volume production are presented and discussed. Considering H^- surface production due to H atoms and positive hydrogen ions, enhancement of H^- production and pressure dependence of H^- production observed experimentally are qualitatively well reproduced in the model calculation, where stripping loss in the extraction and acceleration regions is taken into account. For enhancement of H^$production, so-called electron cooling in the source region, as well as in the extraction region, is not so effective if plasma parameters are initially optimized with the use of a magnetic filter.
  IEEE Transactions on Plasma Science 07/2000; · 1.17 Impact Factor
• Article: Control of Plasma Parameters in RF Negative Ion Sources

  Y. Tauchi, O. Fukumasa
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  ABSTRACT: A long lifetime neutral beam injector (NBI) system is necessary for heating future fusion plasmas. Therefore negative ion sources for NBI system should be constructed by using high frequency discharge plasmas. A radiofrequency discharge plasma is one of the most promising candidate for long lifetime ion sources. We studied production and control of ECR and RF (i e capacitively coupled plasma.) plasmas by using the magnetic filter method.
• Article: Negative Ion Density Distribution in a Volume Negative Ion Source - Its Dependence on Plasma Parameters

  S Mori, Y. Tauchi, O. Fukumasa, M. Hamabe, Y. Takeiri
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  ABSTRACT: In a volume negative ion source, H/sup -/ ions are formed in hydrogen plasmas by dissociative attachment of slow plasma electrons to highly vibrationally excited hydrogen molecules, and these vibrational molecules are produced by energetic electron impact. Production of D/sup -/ ions is believed to be the same as that of H/sup -/ ions. To develop efficient D/sup -/ ion sources, it is important to study production and control of D/sub 2/ plasmas, and to understand difference in the negative ion volume production between H/sub 2/ plasmas and D/sub 2/ plasmas. For this purpose, we discuss isotope effect of H/sup -//D/sup -/ production and to clarify the dependence of negative ion production on plasma parameters by measuring negative ion densities in the source.
• Article: Simulation of photo-detached electrons in negative ion plasmas

  H. Naitou, Y Sakurai, Y. Tauchi, O. Fukumasa, M Yagi, Y. Yamagata, K. Uchino, K Muraoka
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  ABSTRACT: The evolution of laser photo-detached and background electrons in a glow discharge plasma containing negative ions was followed using a two-dimensional particle-in-cell simulation code. Emphasis was placed on the short timescale (20 ns after photo-detachment for the parameters of a typical glow discharge plasma) behaviour because this is the timescale of the recently developed laser Thomson scattering technique combined with photo-detachment. A plasma consisting of background electrons, positive argon ions (Ar^+) and negative oxygen ions (O^-) was treated. The loss of photo-detached electrons from the photo-detachment region quickly forms a potential structure in a short time of 2 ns. The potential traps the remaining photo-detached electrons. The profile of the trapped photo-detached electrons is hollow. The loss of the photo-detached electrons from the photo-detachment region is compensated by the bulk electrons coming from the ambient plasma; the sum of the photo-detached and bulk electron densities in the photo-detachment region remains unchanged for 20 ns because ions are almost immobile in this timescale. This analysis has also revealed the fractions of the photo-detached electrons remaining in the photo-detachment region during the 20 ns to be relatively insensitive to a change in laser beam size and very sensitive to the relative densities of negative ions against background electrons, and to the shape of the velocity distribution function at different angles with respect to the laser beam axis.
• Source

  Available from: yamaguchi-u.ac.jp

  Article: Isotope effect of H^-/D^- volume production in low-pressure H_2/D_2 plasmas : Measurement of VUV emissions and negative ion densities

  O. Fukumasa, S Mori, N. Nakada, Y. Tauchi, M. Hamabe, K. Tsumori, Y. Takeiri
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  ABSTRACT: Isotope effect on H^-/D^- volume production is studied by measuring both VUV emission and negative ion density in the source. In a double plasma type source, under some discharge conditions, extracted D^- currents are nearly the same as H^- currents, although VUV emission intensity (corresponding to production of vibrationally excited molecules) in D_2 plasmas is slightly lower than that in H_2 plasmas. Considering the factor √<2> due to mass difference, D^- ion density in the extraction region of the source is higher than H^- ion density. In another experiment with a rectangular arc chamber, axial distributions of H^-/D^- ion densities in the source are measured directly using a laser photodetachment method. Relationship between H^-/D^- production and plasma parameter control with using a magnetic filter (MF) is discussed. Furthermore, relative intensities of extracted negative ion currents are discussed compared with the negative ion densities in the source. Production and control of D_2 plasmas are well realized with the MF including good combination between the filament position and field intensity of the MF. Extracted H^- and D^- currents depend directly on negative ion densities in the source.
• Article: Production Mechanism of D‾ Ions and Evaluation of D‾ Ion Current Extraction

  O. Fukumasa, H. Naitou, Y. Tauchi, S Mori, A Ando, K Sawada, M. Hamabe, Y. Takeiri, K. Tsumori
• Article: Development of Cesium-free Deuterium Negative Ion Source with Grid Bias Method

  O. Fukumasa, Y. Tauchi, S Mori, J. Okada, Y. Jyobira, T Yoshioka, Y. Takeiri, K. Tsumori
• Article: Development of Cesium-free Deuterium Negative Ion Source with Grid Bias Method

  O. Fukumasa, W. Oohara, Y. Tauchi, T Nakano, T Yoshioka, Y. Takeiri, K. Tsumori
• Article: Characteristics of rf-based Hydrogen Negative Ion Source with Cs Additive

  A Ando, A. Komuro, O. Fukumasa, W. Oohara, Y. Tauchi, M. Hamabe, Y. Takeiri, K. Tsumori, K Ikeda, O. Kaneko
• Article: Development of Deuterium Negative Ion Sources and Its Database Construction

  O. Fukumasa, H. Naitou, S Sakiyama, Y. Tauchi, K Sawada, H Fujita, Y. Otsu, M. Hamabe, K. Tsumori, Y. Takeiri
• Article: Development of Cesium-Free Deuterium/Hydrogen Negative-Ion Source with Metal Catalectic-Ionization Method

  W. Oohara, Y. Tauchi, S. Fujimoto, T Nakano, S. Tashima, O. Fukumasa, Y. Takeiri, K. Tsumori
• Article: Bifurcation in Asymmetric Plasma Divided by a Magnetic Filter

  K. Ohi, H. Naitou, Y. Tauchi, O. Fukumasa
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  ABSTRACT: A magnetic filter (MF) reflecting electrons from both sides can separate a low-temperature and low-density subplasma from a high-temperature and high-density main plasma. The one-dimensional numerical simulation by the particle-in-cell code revealed that, depending on the asymmetry, the plasma divided by the MF behaves dynamically or statically [K. Ohi et al., Physics of Plasmas 8, 23 (2001)]. The transition between the two bifurcated states is discontinuous. In the dynamic state, the autonomous potential oscillation in the subplasma is synchronized with the passage of the shock wave structure generated by the modulated ion beam from the main plasma. The stationary phase of the dynamic state appears after the amplitude of the potential oscillation in the subplasma grows exponentially from the thermal noise. In the static state, the system is stable to the growth of the potential oscillation in the subplasma.
• Source

  Available from: jspf.or.jp

  Article: Catalytic effect on ionization of hydrogen

  W Oohara, O Fukumasa
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  ABSTRACT: In a plasma source development of a hydrogen pair-ion plasma consisting of only hydrogen atomic ions, H + and H − , efficient production of the atomic ions is required. Hydrogen positive ions produced in a PIG discharge are supplied to a catalyst. The ions are converted to the atomic ions on the catalyst surface, and an ionic plasma with very low electron density is generated.