Satoshi Sakiyama

Thermal plasma processing : syntheses of diamond and β"-alumina

Abstract Thermal plasma processing using a plasma jet with high speed and high heat capacity under reduced pressure (≦100 torr) is one of the most promising methods for synthesizing new materials. We have newly developed a thermal plasma reactor composed of a forced constricted type plasma jet generator with a feed ring, and confirmed that this reactor generates stable plasma jets with a high heat capacity under various operating conditions. In this paper, to realize the large area deposition at a high rate, synthesis of diamond films from gas mixtures of CH 4 and H 2 is studied. Synthesis of β″-alumina, thermoelectric materials for the alkali metal thermoelectric converter (AMTEC), from powder mixtures is also discussed.

Spatial control of electron energy distribution function in a magnetically filtered multicusp plasma source

Using a movable magnetic filter, a technique to control plasma parameters spatially has been investigated in a multicusp plasma source. At any filter position, plasma parameters change steeply across the magnetic filter. Mainly, a multicusp plasma source is divided into two parts, i.e., a source plasma region with energetic electrons and a diffused plasma region. In the latter region, the high-energy component of electrons is eliminated thoroughly by the localized magnetic field of the filter.

Diagnosis of Asymmetric Thermal Plasma Jet Using Computer Tomography Technique

In order to clarify the feasibility of application of the computer tomography technique for the diagnosis of an asymmetrical plasma jet, the heat transfer flux of the jet is measured using a water-cooled calorimetric probe. The asymmetric plasma jet is generated by injecting the feed gas into the jet perpendicular to the jet axis. The algebraic reconstruction technique (ART) is used as the reconstruction method. With increasing the feed-gas flow rate, the asymmetry of the heat transfer flux profile of the jet is found to increase, by means of the computer tomography technique.

Control of reactive plasmas in a multicusp plasma source equipped with a movable magnetic filter

With the use of both a movable magnetic filter and a plasma grid, plasma parameters (H2‐CH4 or Ar‐CH4 plasmas) are spatially well controlled. At any filter position, plasma parameters change steeply across the magnetic filter. Then, a plasma source is divided into the two parts, i.e., the source plasma region (high density plasma with energetic electrons) and the diffused plasma region (low density and low‐temperature plasma without energetic electrons). Plasma parameters in the diffused plasma are well controlled by changing the plasma grid potential. The role of the magnetic filter (i.e., preferential reflection of energetic electrons) is well clarified by computer simulation. The relation between plasma parameters and some species of neutral radicals is also briefly discussed.

Integrated synthesis of AMTEC electrode by using controlled thermal plasma processing

Abstract Thermoelectric materials (β″-alumina) for the alkali metal thermoelectric converter (AMTEC) have been synthesized with the use of a thermal plasma reactor based on the forced constricted type plasma jet generator. It is reconfirmed that the powder mixing ratio (i.e. the ratio between α-Al 2 O 3 , Na 2 CO 3 and MgO), jet power and substrate position, strongly affect the synthesis of β″-alumina. Besides these, the synthesis of β″-alumina is also enhanced in the high-temperature region by oxygen injection. Those dependences are correlated with jet temperature and particle heating. The metal electrode of molybdenum is also prepared by spraying Mo powders. Porosity of the prepared films could be well controlled by varying the pressure.

Synthesis of diamond using low pressure plasma jet

With the use of the forced constricted type plasma jet, the synthesis of diamond is attemped under low pressure, in order to realize large area deposition at a high rate. The effect of the ambient gas pressure on the deposition rate and deposition area of the film is studied. It is clarified that the deposition area is extended markedly with decreasing gas pressure. Furthermore, diamond films are successfully synthesized without the large decrease of the deposition rate, even at 5 Torr.

Wall effects on the percentage of atomic ions in a hydrogen plasma

Abstract The ratio of ion species in hydrogen plasma is calculated numerically by using a particle balance model, where the recombination factor for hydrogen atoms at the wall is treated as another plasma parameter.

Relationship between Control of Reactive Plasmas with Magnetic Filter and Formation of Thin Films

Plasma parameters (CH 4 /H 2 + Ar plasmas) are spatially well controlled using a movable magnetic filter. At any filter position, plasma parameters change dramatically across the magnetic filter. The plasma is divided into two parts, the source plasma region (high density plasmas with energetic electrons) and the diffused plasma region (low electron-temperature plasmas without energetic electrons). Carbon thin films are prepared well in the diffused plasma region. The effects of bias potential of the substrate and control of neutral radicals on formation of thin films are discussed briefly.

Experimental test of H− volume production process in a hydrogen discharge

To investigate electron energy dependence of pure H− volume production, we have recently designed a double‐plasma‐type negative ion source. In this source, both energy and density of fast electrons are well controlled. With the use of this source, the effect of fast electrons on H− production, i.e., the so‐called two‐step process of H− production, is discussed.

Isotope effects in an electron beam excited negative ion source

Results which focus on comparing operation in hydrogen and deuterium are presented. Measurements of plasma parameters, including electron density, electron temperature, electron energy distribution function and extracted negative ion current, have been made in the source and extractor regions of an electron beam excited negative ion source. For the same operating conditions, negative ion current is found to be higher in deuterium than in hydrogen.