M. Wada

Doshisha University, Kioto, Kyōto, Japan

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Publications (200)178.42 Total impact

  • 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.
    Applied Physics Reviews 06/2015; 2(2):021305. DOI:10.1063/1.4921298
  • 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.
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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.
    Journal of Nuclear Materials 12/2014; 463. DOI:10.1016/j.jnucmat.2014.12.026 · 1.87 Impact Factor
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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.
    Review of Scientific Instruments 11/2014; 85(11-11):-. DOI:10.1063/1.4886764 · 1.61 Impact Factor
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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.
    The Review of scientific instruments 02/2014; 85(2):02C311. DOI:10.1063/1.4855455 · 1.61 Impact Factor
  • M R Vasquez · S Tokumura · T Kasuya · M Wada
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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.
    The Review of scientific instruments 02/2014; 85(2):02A717. DOI:10.1063/1.4832061 · 1.61 Impact Factor
  • 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.
    The Review of scientific instruments 02/2014; 85(2):02B114. DOI:10.1063/1.4833928 · 1.61 Impact Factor
  • 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.
    The Review of scientific instruments 02/2014; 85(2):02C106. DOI:10.1063/1.4857255 · 1.61 Impact Factor
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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.
    The Review of scientific instruments 02/2014; 85(2):02B132. DOI:10.1063/1.4860396 · 1.61 Impact Factor
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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.
    The Review of scientific instruments 02/2014; 85(2):02A720. DOI:10.1063/1.4833918 · 1.61 Impact Factor
  • 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.
    The Review of scientific instruments 02/2014; 85(2):02A714. DOI:10.1063/1.4830356 · 1.61 Impact Factor
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    ABSTRACT: An 80 mm diameter 80 mm long RF sputter type self-extraction negative ion source equipped with a metal sputter target has been tested to investigate the performance of producing beams of negative aluminum (Al) ions. An RF power at 13.56 MHz is directly supplied to a 60 mm diameter target containing a cylindrical and ring permanent magnets to form planar magnetron magnetic field geometry. The target is self-biased to a DC potential at about -250 V with respect to the plasma, and negative ions produced at the surface are self-extracted from the target across the sheath to reach the ion beam extraction hole. Injection of cesium into the discharge enhanced the amount of Al- ions but it also enlarged the impurity ion beam current.
    02/2013; 1515:491-497. DOI:10.1063/1.4792820
  • M. Wada · M. Bacal · T. Kasuya · S. Kato · T. Kenmotsu · M. Sasao
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    ABSTRACT: Exposure to Cs added hydrogen discharge makes surface of plasma grid of a negative hydrogen ion source covered with Cs and hydrogen. A Monte-Carlo particle simulation code ACAT was run to evaluate the effects due to adsorbed Cs and H atoms upon the angular and energy distributions of H atoms leaving the surface. Accumulation of H atoms on the surface reduces particle reflection coefficients and the mean energy of backscattered H atoms. Angular distributions of H atoms reflected from the hydrogen covered surface tend to be under-cosine at lower energies. Desorption of adsorbed H atoms is more efficient for hydrogen positive ions than for Cs positive ions at lower incident energy. At higher energy more than 100 eV, Cs ions desorb adsorbed H atoms more efficiently than hydrogen ions.
    02/2013; 1515:59-65. DOI:10.1063/1.4792770
  • M. Bacal · M. Wada
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    ABSTRACT: The purpose of the present work is to provide a method for calculating the negative hydrogen ion yield due to fast and thermal ions and atoms versus the surface work function. The value of the decay factor in Rasser's equation is re-examined, to make possible the use of this equation to this aim. The analysis of the data from two experiments lead to two different values for the decay factor. The lower value, 2.13×10-5 eV s/m, allows to determine the yield of backscattered negative ions. The higher value, 6.4×10-5 eV s/m, leads to the total yield. The fractions of the negative ions produced by backscattering and desorption are determined.
    02/2013; 1515:41-48. DOI:10.1063/1.4792768
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    ABSTRACT: An electron cyclotron resonance condition at 14 GHz frequency has been realized for a compact negative hydrogen (H-) ion source with the discharge chamber made of a 55.5 mm diameter 42.5 mm long alumina cup. Two microwave launching systems had excited a hydrogen plasma in the discharge chamber: one that injects with the electric field perpendicular to the static magnetic field: and the other inject with the field parallel to the static field. The ion source performance is found always better when the electric field of the microwave is aligned parallel to the ECR magnetic field, and the reflected power has become nearly zero for this configuration when the position of a tuner to form a microwave cavity around the plasma is properly adjusted. The magnetic field structure near the extraction electrode is being optimized to increase H- ion current.
    02/2013; DOI:10.1063/1.4792808
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    ABSTRACT: Extraction of ions with energies below 100 eV has been demonstrated using a hot-cathode multi-cusp ion source equipped with extraction electrodes made of thin wires. Two electrode geometries, a single-electrode system, and a dual-electrode system were built and tested. The single-electrode configuration showed high ion beam current densities at shorter distances from the electrode but exhibited rapid attenuation as the distance from the electrode increased. Beam angular spread measurements showed similar beam divergence for both electrode configurations at low plasma densities. At high plasma densities and low extraction potentials, the single-electrode system showed the angular spread twice as large as that of the dual-electrode system. Energy distribution analyses showed a broader energy spread for ion beams extracted from a single-electrode set-up.
    11/2012; DOI:10.1063/1.4766574
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    ABSTRACT: Positive ions of aluminum (Al+) have been extracted from a compact ion source of 8 cm diameter, 9 cm long inside volume. A 7.7 cm diameter 7.5 cm long cylindrical cage made of 1 mm thick Al sheet metal served as an electrode of radio frequency discharge at 13.56 MHz. Magnets attached to the water cooled wall of the ion source created planar and cylindrical magnetron magnetic field geometry at the surface of the cage. The measured DC self-bias voltage of the cage electrode with respect to the ion source wall was more positive than -10 V for source operating pressure above 1.2 Pa with 100 W RF discharge power. Relative amount of Al+ ion current had increased as additional DC bias voltage was applied to the electrode from a separate DC power supply. However, frequent arcing prohibited stable operation of the ion source for DC target bias larger than 100 V.
    11/2012; DOI:10.1063/1.4766570
  • T Kenmotsu · M Wada
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    ABSTRACT: Atomic collision processes associated with surface production of negative hydrogen ions (H(-)) by particle reflection at molybdenum surface immersed in hydrogen plasma have been investigated. To calculate sputtering yields of Cs, as well as energy spectra and angular distributions of reflected hydrogen atoms from molybdenum surface by H(+) ion and Cs(+) ion bombardments, a Monte Carlo simulation code ACAT (Atomic Collision in Amorphous Target) was run with the corresponding surface conditions. A fractal surface model has been developed and adopted to ACAT for evaluating the effect due to roughness of target material. The results obtained with ACAT have indicated that the retention of hydrogen atoms leads to the reduction in sputtering yields of Cs, and the surface roughness does largely affect the sputtering yields of Cs.
    The Review of scientific instruments 02/2012; 83(2):02A722. DOI:10.1063/1.3673624 · 1.61 Impact Factor
  • S Tokumura · T Kasuya · M Vasquez · S Maeno · M Wada
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    ABSTRACT: The two-electrode extractor system made of 0.1 mm diameter tungsten wires separated by 0.7 mm has formed an argon ion beam with 50 V extraction potential. Energy spreads of the extracted beams were typically less than 2 eV when the beam current density was low. The beam intensity rapidly decreased as the distance between the extractor and the beam detector increased, indicating space charge limited transport of the beam. Problems associated with the emittance measurements are also discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3672475]
    The Review of scientific instruments 02/2012; 83(2):02B716. DOI:10.1063/1.3672475 · 1.61 Impact Factor
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    ABSTRACT: A pair of permanent magnets has formed enough intensity to realize electron cyclotron resonance condition for a 14 GHz microwave in a 2 cm diameter 9 cm long alumina discharge chamber. A three-electrode extraction system assembled in a magnetic shielding has formed a stable beam of negative hydrogen ions (H(-)) in a direction perpendicular to the magnetic field. The measured H(-) current density was about 1 mA∕cm(2) with only 50 W of discharge power, but the beam intensity had shown saturation against further increase in microwave power. The beam current decreased monotonically against increasing pressure.
    The Review of scientific instruments 02/2012; 83(2):02A716. DOI:10.1063/1.3672473 · 1.61 Impact Factor

Publication Stats

586 Citations
178.42 Total Impact Points


  • 1992–2014
    • Doshisha University
      • • Graduate School of Science and Engineering
      • • Faculty of Life and Medical Sciences
      • • Department of Electronics
      • • Faculty of Science and Engineering
      Kioto, Kyōto, Japan
  • 2001–2007
    • Konan University
      • Department of Information Science and System Engineering
      Kōbe-shi, Hyogo-ken, Japan
  • 2005
    • Tohoku University
  • 1996–2000
    • The University of Tokushima
      • • Department of Electrical and Electronic Engineering
      • • Faculty of Engineering
      Tokushima-shi, Tokushima-ken, Japan