M. Wada

Doshisha University, Kioto, Kyoto, Japan

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Publications (204)193.37 Total impact


  • No preview · Article · Feb 2016 · Physica Scripta
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    ABSTRACT: Wavelength spectra of Balmer-α light from plasmas in the extraction region of the Large Helical Device-R&D negative ion source, or the LHD one-third ion source have exhibited a blue shift as a negative bias voltage was applied to the plasma grid. The blue shift increased as the negative bias voltage with respect to the local plasma potential was increased. The measured spectra were compared with the velocity distributions of surface reflected hydrogen atoms calculated by atomic collisions in amorphous target code. The arc power and the source H2 pressure also affected the shift and broadening in the observed Balmer-α spectra. The possibility of identifying the negative hydrogen ions produced at the low work function plasma grid surface by high resolution spectroscopy is discussed.
    No preview · Article · Feb 2016 · Review of Scientific Instruments
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    ABSTRACT: Dust particles of μm size produced by a monoplasmatron ion source are observed by a laser light scattering. The scattered light signal from an incident laser at 532 nm wavelength indicates when and where a particle passes through the ion beam transport region. As the result, dusts with the size more than 10 μm are found to be distributed in the center of the ion beam, while dusts with the size less than 10 μm size are distributed along the edge of the ion beam. Floating potential and electron temperature at beam transport region are measured by an electrostatic probe. This observation can be explained by a charge up model of the dust in the plasma boundary region.
    No preview · Article · Feb 2016 · Review of Scientific Instruments
  • Vasquez, M.R., Jr · M. Wada
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    ABSTRACT: An ion source with a remote plasma chamber excited by a 13.56 MHz radio frequency power was used for low-energy broad ion beam extraction. Optical emission spectral analyses showed the sputtering and postionization of a liquid gallium (Ga) target placed in a chamber separated from the source bombarded by argon (Ar) plasma guided by a bent magnetic field. In addition, an E × B probe successfully showed the extraction of low-energy Ga and Ar ion beams using a dual-electrode extractor configuration. By introducing dilute amounts of nitrogen gas into the system, formation of thin Ga-based films on a silicon substrate was demonstrated as determined from X-ray diffraction and X-ray reflectivity studies.
    No preview · Article · Feb 2016 · Review of Scientific Instruments
  • Y. Kuwata · T. Kasuya · N. Miyamoto · M. Wada
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    ABSTRACT: A 20 cm long 10 cm wide microwave plasma source was realized by inserting two 20 cm long 1.5 mm diameter rod antennas into the plasma. Plasma luminous distributions around the antennas were changed by magnetic field arrangement created by permanent magnets attached to the source. The distributions appeared homogeneous in one direction along the antenna when the spacing between the antenna and the source wall was 7.5 mm for the input microwave frequency of 2.45 GHz. Plasma density and temperature at a plane 20 cm downstream from the microwave shield were measured by a Langmuir probe array at 150 W microwave power input. The measured electron density and temperature varied over space from 3.0 × 109 cm−3 to 5.8 × 109 cm−3, and from 1.1 eV to 2.1 eV, respectively.
    No preview · Article · Feb 2016 · Review of Scientific Instruments
  • Vasquez, M.R., Jr · M. Wada
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    ABSTRACT: Low-energy argon beams were extracted from a dual-chamber ion source system. The first chamber is a quartz cylinder where dense inductively coupled plasmas were produced using 13.56 MHz radio frequency (rf) power. The discharge was driven into an adjacent chamber which acts as a reservoir for ion beam extraction using a dual-electrode extractor configuration. Extraction of ions from the second chamber with energies in the 100 eV range was achieved while minimizing fluctuations induced by the rf signal. A custom-built retarding potential analyzer was used to analyze the effectiveness of ion beam transport using the remote plasma chamber. Well-defined beams were extracted between 60 and 100 V extraction potentials at 50-100 W rf powers. An increase in rf power resulted in an increase in average ion energy, increase in ion current density while the energy spread remains constant.
    No preview · Article · Feb 2016 · Review of Scientific Instruments
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    ABSTRACT: Recent research results on negative-ion-rich plasmas in a large negative ion source have been reviewed. Spatial density and flow distributions of negative hydrogen ions (H−) and positive hydrogen ions together with those of electrons are investigated with a 4-pin probe and a photodetachment (PD) signal of a Langmuir probe. The PD signal is converted to local H− density from signal calibration to a scanning cavity ring down PD measurement. Introduction of Cs changes the slope of plasma potential local distribution depending upon the plasma grid bias. A higher electron density H2plasma locally shields the bias potential and behaves like a metallic free electron gas. On the other hand, the bias and extraction electric fields penetrate in a Cs-seeded electronegative plasma even when the electron density is similar. Electrons are transported by the penetrated electric fields from the driver region along and across the filter and electron deflection magnetic fields. Plasma ions exhibited a completely different response against the penetration of electric fields.
    No preview · Article · Feb 2016 · Review of Scientific Instruments
  • M. Bacal · M. Wada
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    ABSTRACT: Negative hydrogen/deuterium ions can be formed by processes occurring in the plasma volume and on surfaces facing the plasma. The principal mechanisms leading to the formation of these negative ions are dissociative electron attachment to ro-vibrationally excited hydrogen/deuterium molecules when the reaction takes place in the plasma volume, and the direct electron transfer from the low work function metal surface to the hydrogen/deuterium atoms when formation occurs on the surface. The existing theoretical models and reported experimental results on these two mechanisms are summarized. Performance of the negative hydrogen/deuterium ion sources that emerged from studies of these mechanisms is reviewed. Contemporary negative ion sources do not have negative ion production electrodes of original surface type sources but are operated with caesium with their structures nearly identical to volume production type sources. Reasons for enhanced negative ion current due to caesium addition to these sources are discussed.
    No preview · Article · Jun 2015 · Applied Physics Reviews
  • Source
    M. Bacal · M. Sasao · M. Wada · R. McAdams
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    ABSTRACT: The plasma grid is electrically biased with respect to other parts of source chamber wall in both volume sources and sources seeded with alkali metals. The roles of the plasma grid in these two kinds of sources will be described. The main functions of the plasma grid in volume sources are: optimizing the extracted negative ion current, reducing the co-extracted electron current, controlling the axial plasma potential profile, recycling the hydrogen atoms to molecules, concentrating the negative ions near its surface and, when biased positive, depleting the electron population near its surface. These functions are maintained in the sources seeded with alkali metals. However an additional function appears in the Cs seeded sources, namely direct emission of negative ions under positive ion and neutral hydrogen bombardment.
    Full-text · Conference Paper · Apr 2015
  • Source
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    ABSTRACT: Balmer-α light emission from the extraction region of the LHD one-third ion source has shown a characteristic Doppler broadening in the wavelength spectrum detected by a high resolution spectrometer. The spectrum resembles Gaussian distribution near the wavelength of the intensity peak, while it has an additional component of a broader foot. The measured broadening near the wavelength of the intensity peak corresponds to 0.6 eV hydrogen atom temperature. The spectrum exhibits a larger expansion in the blue wing which becomes smaller when the line of sight is tilted toward the driver region from the original observation axis parallel to the plasma grid. A surface collision simulation model predicts the possibility of hydrogen reflection at the plasma grid surface to form a broad Balmer-α light emission spectrum.
    Preview · Conference Paper · Apr 2015
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    ABSTRACT: Hydrogen ion reflection properties have been investigated following the injection of H+, H2+ and H3+ ions onto a polycrystalline W surface. Angle- and energy-resolved intensity distributions of both scattered H+ and H− ions are measured by a magnetic momentum analyzer. We have detected atomic hydrogen ions reflected from the surface, while molecular hydrogen ions are unobserved within our detection limit. The reflected hydrogen ion energy is approximately less than one-third of the incident beam energy for H3+ ion injection and less than a half of that for H2+ ion injection. Other reflection properties are very similar to those of monoatomic H+ ion injection. Experimental results are compared to the classical trajectory simulations using the ACAT code based on the binary collision approximation.
    No preview · Article · Dec 2014 · Journal of Nuclear Materials
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    ABSTRACT: A 12 × 12 pixel detector has been developed and used in a laboratory experiment for lost fast-ion diagnostics. With gamma rays in the MeV range originating from nuclear reactions 9Be(α, nγ)12C, 9Be(d, nγ)12C, and 12C(d, pγ)13C, a high purity germanium (HPGe) detector measured a fine-energy-resolved spectrum of gamma rays. The HPGe detector enables the survey of background-gamma rays and Doppler-shifted photo peak shapes. In the experiments, the pixel detector produces a gamma-ray image reconstructed from the energy spectrum obtained from total photon counts of irradiation passing through the detector's lead collimator. From gamma-ray image, diagnostics are able to produce an analysis of the fast ion loss onto the first wall in principle.
    No preview · Article · Nov 2014 · Review of Scientific Instruments
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    ABSTRACT: Angle-resolved energy distribution functions of positive and negative hydrogen ions produced from a rough-finished Si surface under 1 keV proton irradiation have been measured. The corresponding distribution from a crystalline surface and a carbon surface are also measured for comparison. Intensities of positive and negative ions from the rough-finished Si are substantially smaller than those from crystalline Si. The angular distributions of these species are broader for rough surface than the crystalline surface. No significant temperature dependence for positive and negative ion intensities is observed for all samples in the temperature range from 300 to 400 K.
    No preview · Article · Feb 2014 · The Review of scientific instruments
  • M Wada · T Kasuya · T Kenmotsu · M Sasao
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    ABSTRACT: A numerical simulation code, Atomic Collision in Amorphous Target, has been run to clarify the effects due to the incident angle of hydrogen flux onto surface collision cascade in the subsurface region of a Cs covered Mo plasma grid. The code has taken into account the threshold energy for negative hydrogen (H(-)) ions to leave the surface. This modification has caused the shift of energy distribution functions of H(-) from that of hydrogen atoms leaving the surface. The results have shown that large incident angle of hydrogen particle tilt the angular distribution of reflection component, while it caused a small effect onto the angular distribution of desorption component. The reflection coefficient has increased, while the desorption yield has decreased for increased angle of incidence measured from the surface normal.
    No preview · Article · Feb 2014 · The Review of scientific instruments
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    ABSTRACT: Discharge characteristics in the upstream as well as in the downstream regions of a 50-eV positive ion beam were measured along the beam axis. Single- and dual-electrode configurations made of 0.1-mm diameter tungsten wires were tested. By varying the upstream discharge parameters, the shape of the sheath edge around the extractors, which can either be "planar" or "cylindrical," can be controlled. The sheath eventually affected the simultaneous extraction of ions and neutralizing electrons. The dual-electrode configuration at the lower discharge current, revealed a homogeneous discharge downstream. At this condition, the edge of the sheath can be inferred to be "planar" which allowed the uniform extraction and propagation of low-energy ions at longer distances. The dual-electrode configuration was capable of transmitting low-energy ions up to 70 mm downstream.
    No preview · Article · Feb 2014 · The Review of scientific instruments
  • N Yamada · T Kasuya · N Tsubouchi · M Wada
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    ABSTRACT: A 70 mm diameter 70 mm long compact ion source equipped with a hollow sputtering target has been designed and tested. The hollow sputtering target serves as the radio frequency (RF) plasma excitation electrode at 13.56 MHz. A stable beam of Cu+ has been extracted when Ar was used as the discharge support gas. In the extracted beam, Cu+ had occupied more than 85% of the total ion current. Further increase in Cu+ ions in the beam is anticipated by increasing the RF power and Ar pressure. (C) 2014 AIP Publishing LLC.
    No preview · Article · Feb 2014 · The Review of scientific instruments
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    ABSTRACT: The plasma electrode structure of a 14 GHz ECR ion source was modified to enlarge the plasma volume of low electron temperature region. The result shows that the extracted beam current reached about 0.6 mA/cm(2) with about 40 W microwave power. To investigate the correlation between the volume of the low electron temperature region and the H(-) current, a vacuum ultraviolet (VUV) spectrometer had been installed to observe light emission in the VUV wavelength range from the plasma. From the results of the negative ion beam current and that from VUV spectrometry, production rate of vibrationally excited hydrogen molecule seems to be enhanced by increasing the volume of low electron temperature region.
    No preview · Article · Feb 2014 · The Review of scientific instruments
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    ABSTRACT: We study influence of electric field penetration into H(-) ion source plasma with three-electrode beam extraction system. Clear change in the plasma potential due to the field penetration is observed in case of low gap voltage between a plasma electrode and an extraction electrode. Influence of lens voltage on the second electrode, which is normally utilized to focus the extracted beam, on ion source plasma is evaluated separating contributions of H(-) density in the plasma and extraction probability of H(-) ions from the plasma by two kinds of photodetachment techniques. In our operation condition, we found that the lens voltage is also useful to enhance the H(-) density in the plasma, though it negatively affects the extraction probability.
    No preview · Article · Feb 2014 · The Review of scientific instruments
  • N Miyamoto · Y Okajima · M Wada
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    ABSTRACT: Argon ion beam fluctuation from an AC filament driven Bernas-type ion source is observed. The ion beam was measured by an 8 measurement elements beam profile monitor. The amplitude of the beam current fluctuation stayed in the same level from 100 Hz to 1 kHz of the filament heating frequency. The beam current fluctuation frequency measured by the beam profile monitor was equal to the frequency of the AC filament operation. The fluctuation amplitudes of the beam current by AC operation were less than 7% and were in the same level of the DC operation.
    No preview · Article · Feb 2014 · The Review of scientific instruments
  • M. Sasao · M. Wada · M. Isobe
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    ABSTRACT: Among various methods proposed for alpha-particles loss measurement, we studied on those by measuring gamma rays of three cases, from (1) nuclear reactions induced by alpha particles, (2) those from short-life-time activities and (3) those from long-life-time activities induced by alpha particles. The time evolution of local alpha flux may possibly be measured by using the 9Be (a, n) 12C reaction (1). Using the same system, but with a target set up close to the first wall, activation measurement on site right after turning-off the discharge is possible (2). Nuclear reaction, 25Mg (a, p) 28Al, that produce radioisotopes of short lifetime of 2.2 minutes in one of the best candidates. As to the activation to a long lifetime (3), it is predicted that the gamma ray yield from 19F (a, n) 22Na reaction is enough for the measurement at the reactor site.
    No preview · Article · Jan 2014 · AIP Conference Proceedings

Publication Stats

673 Citations
193.37 Total Impact Points

Institutions

  • 1992-2016
    • Doshisha University
      • • Graduate School of Science and Engineering
      • • Faculty of Life and Medical Sciences
      • • Department of Electronics
      • • Faculty of Science and Engineering
      Kioto, Kyoto, Japan
  • 1996-2000
    • The University of Tokushima
      • Department of Electrical and Electronic Engineering
      Tokushima-shi, Tokushima-ken, Japan