M. Wada

Doshisha University, Kioto, Kyōto, Japan

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Publications (190)154.98 Total impact

  • [Show abstract] [Hide abstract]
    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.
    The Review of scientific instruments 02/2014; 85(2):02C106. · 1.52 Impact Factor
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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. · 1.52 Impact Factor
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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. · 1.52 Impact Factor
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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. · 1.52 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. · 1.52 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. · 1.52 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. · 1.52 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. 01/2014; 85(11):-.
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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;
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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;
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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;
  • 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;
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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;
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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;
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    ABSTRACT: Beams of argon ions with energies less than 50 eV were extracted from an ion source through a wire electrode extractor geometry. A retarding potential energy analyzer (RPEA) was constructed in order to characterize the extracted ion beams. The single aperture RPEA was used to determine the ion energy distribution function, the mean ion energy and the ion beam energy spread. The multi-cusp hot cathode ion source was capable of producing a low electron temperature gas discharge to form quiescent plasmas from which ion beam energy as low as 5 eV was realized. At 50 V extraction potential and 0.1 A discharge current, the ion beam current density was around 0.37 mA/cm(2) with an energy spread of 3.6 V or 6.5% of the mean ion energy. The maximum ion beam current density extracted from the source was 0.57 mA/cm(2) for a 50 eV ion beam and 1.78 mA/cm(2) for a 100 eV ion beam.
    The Review of scientific instruments 02/2012; 83(2):023301. · 1.52 Impact Factor
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    ABSTRACT: A strongly focusing He(+) ion beam source equipped with concave multi-aperture electrodes was developed for production of He(-) through a charge exchange cell. The beam was extracted at a voltage less than 20 kV from 301 apertures distributed in an area of 100 mm φ, and focused at 750 mm distance. The beam current and the beam size of 2 A and 20 mm in diameter, respectively, were achieved with an arc power less than 10 kW. The optimum perveance was obtained at 0.02 A∕kV(1.5) at the beam energy less than 20 keV which is suitable for the conversion to He(-) in an alkali vapor cell.
    The Review of scientific instruments 02/2012; 83(2):02B120. · 1.52 Impact Factor
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    ABSTRACT: A thin-walled aluminum (Al) hollow electrode has been inserted into an ion source to serve as an electrode for a radio frequency magnetron discharge. The produced plasma stabilized by argon (Ar) gas sputters the Al electrode to form a beam of Al(+) and Ar(+) ions. The total beam current extracted through a 3 mm diameter extraction hole has been 50 μA, with the Al(+) ion beam occupying 30% of the total beam current.
    The Review of scientific instruments 02/2012; 83(2):02B715. · 1.52 Impact Factor
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    ABSTRACT: Proof of principle experiments of neutral helium beam production for alpha particle diagnostics was carried out on a test stand. Negative helium ions were produced in the Li charge exchange cell, in which stable and long time operation was possible. He(-) beam was accelerated to 157 keV. Finally, He(0) beam was successfully produced after the flight in the drift-tube through the auto-electron-detachment process from He(-) to He(0). A neutral beam detector using a pyroelectric device was also developed to measure He(0) beam intensity. The metastable component in the neutral helium beam was found to be less than 2%.
    The Review of scientific instruments 02/2012; 83(2):02B115. · 1.52 Impact Factor
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    ABSTRACT: A tungsten filament cathode has been operated with an ac heating current to excite a plasma in a linear magnetic field. Both the discharge current and the ion saturation current in plasma near the extraction hole of the ion source exhibited fluctuations. The discharge current fluctuated with the amplitude less than 2% of the average, and the frequency two times the frequency of the heating current. Fluctuation amplitude of the ion saturation current was about 10% of the average, while the frequency was the same as that of the heating current. The ac operation has prolonged the lifetime of a hot filament cathode by about 50%.
    The Review of scientific instruments 02/2012; 83(2):02B910. · 1.52 Impact Factor
  • 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. · 1.52 Impact Factor

Publication Stats

385 Citations
154.98 Total Impact Points

Institutions

  • 1992–2014
    • Doshisha University
      • • Faculty of Life and Medical Sciences
      • • Department of Electronics
      Kioto, Kyōto, Japan
  • 2005–2012
    • Tohoku University
      • Graduate School of Engineering
      Japan
  • 1992–2012
    • National Institute for Fusion Science
      Tokitsu-chō, Gifu, Japan
  • 2008–2010
    • Tokushima Bunri University
      Tokusima, Tokushima, Japan
    • University of the Philippines Diliman
      • College of Engineering
      Diliman, Central Luzon, Philippines
  • 2001–2007
    • Konan University
      • Department of Information Science and System Engineering
      Kōbe-shi, Hyogo-ken, Japan
  • 1996–2000
    • The University of Tokushima
      • Department of Electrical and Electronic Engineering
      Tokushima-shi, Tokushima-ken, Japan
  • 1999
    • University of the Philippines – Philippine General Hospital
      Manila, National Capital Region, Philippines