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  • 1
    Electronic Resource
    Electronic Resource
    High-current negative-ion beam acceleration with a large negative-ion source for large helical device-neutral beam injection system : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 977-979 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large hydrogen negative-ion source was constructed as a prototype one for the negative-ion-based neutral beam injection (NBI) system in large helical device. The ion source is designed to produce 180 keV-40 A of the negative ion beam with a current density of 40 mA/cm2, and is a cesium-seeded volume production source characterized by the external magnetic filter. The arc chamber of multicusp bucket is rectangular of 35 cm×145 cm in cross section and 21 cm in depth. The accelerator is a three-grid single-stage one, and the total grid area is 25 cm×125 cm, which is divided into five sections. The ion source was installed on the negative-ion-based NBI test-stand, and using one section of the grid 5.5 A of the negative-ion beam was produced at a gas pressure of 1.8 mTorr corresponding to a current density of 27.5 mA/cm2. The extracted electron current is low of 50% of the negative ion current, and the acceleration efficiency, defined as the negative ion current divided by the acceleration drain current, is more than 75%. The ion source operation with the full grid area has just started, and, so far, 21 A of the negative ion beam was obtained. The large area beam has been successfully focused by both the geometrical arrangement of five grid sections and the aperture displacement technique of the grounded grid. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148606
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  • 2
    Electronic Resource
    Electronic Resource
    High current H− ion sources for the large helical device neutral beam injector : Proceedings of the 7th international conference on ion sources (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 920-922 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two large helical device–neutral beam injector (LHD–NBI) ion sources were fabricated and tested in the test stand for producing a beam of 180 keV×40 A with H− ions. They are Cesiated multicusp ion sources with a rectangular discharge chamber and a single stage multihole accelerator. These are scaled up from the 16 A H− ion sources in the National Institute for Fusion Science (NIFS). A plasma source with a high aspect ratio was operated stably with an arc power up to ∼300 kW for 10 s, after balancing of the electron emission from the filaments was made. A satisfactorily dense and uniform plasma without mode flip was produced. Electrons accompanied by H− ions were reduced by an extraction grid with the electron trap, instead of straight holes. The electron beam component caused by the stripping of electrons from H− ions was detected with an array of calorimeters at the bottom of the connecting duct. At the first stage of the test, one of the five segment grids of the accelerator was installed. An H− ion current of 5.5 A with a current density of 27.5 mA/cm2 for 0.6 s was obtained with an arc power of 135 kW with Cs introduction. A high arc power efficiency for H− ions was observed. The intense cusp field is considered to be the important factor to improve this. The beam divergence angle at 10.4 m downstream was ∼10 mrad. Since these results satisfied our design, a full segment accelerator was tested in the next stage. Beam conditioning for five segment grids is underway. So far, an H− current of 21.0 A has been obtained at 106 keV for 0.6 s. As a result, we had good prospects for achieving the full specification of LHD–NBI ion sources, especially for achieving higher current and focused beam as well as for long pulse. The neutral beam injection experiment for the LHD is scheduled to start in the middle of 1998. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148543
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  • 3
    Electronic Resource
    Electronic Resource
    Six-fold coordinated silicon at grain boundaries in sintered α-Al2O3 (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 191-193 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM) have been carried out on Si-doped sintered α-Al2O3. HRTEM shows that there is no amorphous phase at grain boundaries. The Si-segregated boundary is found to be much more sensitive to irradiation damage than undoped Al2O3 grain boundaries. AEM with energy dispersive x-ray spectroscopy (EDS) shows the significant segregation of Si at grain boundaries, and AEM with electron energy-loss spectroscopy (EELS) reveals the existence of six-fold coordinated Si at the grain boundaries. The theoretical calculations obtained by the molecular orbital method support the data obtained by EELS. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120681
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  • 4
    Electronic Resource
    Electronic Resource
    Back-channel-oxidized a-Si:H thin-film transistors (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3993-3999 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a back-channel-oxidized thin-film transistor (TFT) structure which does not require the conventional etching of the n+-a-Si:H layer from the channel region. Key processes in the fabrication of this structure are the deposition of a very thin (less than 10 nm) n+-a-Si:H layer with low resistivity (∼50 Ω cm), and an oxygen plasma treatment to change the n+-a-Si:H layer above the channel region into dielectric oxide. With a thin (∼50 nm) a-Si:H layer, the back-channel-oxidized TFT structure makes it possible to obtain much better "ON" characteristics than are obtained with conventional channel-etched TFTs. To gain insight into the underlying physical mechanism we investigated the back-channel electrical characteristics of both types of TFTs as a function of temperature, and found that back-channel-oxidized TFTs had much better back-channel characteristics than channel-etched TFTs, which is due to a lower density of back-channel interface states. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368579
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