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  • 11
    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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  • 12
    Electronic Resource
    Electronic Resource
    Long-pulse operation of a cesium-seeded high-current large negative ion source (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2012-2019 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-power large negative ion source has been operated for a long pulse duration. A three-grid single-stage accelerator is used, where the extraction grid is shaped so that the secondary electrons generated on the extraction grid would be prevented from leaking into the acceleration gap. A stable long-pulse arc discharge with an arc power of 100 kW has been obtained over 15 s by balancing an individual arc current flowing through each filament. The cesium-seeded operation is not influenced by a temperature rise over 100 °C of the plasma grid during the long-pulse arc discharge. As a result, 330 kW (91 keV–3.6 A) of the negative ion beam was produced stably for 10 s from an area of 25 cm×26 cm, where the current density was 21 mA/cm2 and the negative ion power density was 1.9 kW/cm2. The neutralization efficiency of accelerated negative ions has been measured including the residual positive and negative ion ratios by the water calorimetry of the beam dumps. The result agrees well with the calculation result. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148089
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  • 13
    Electronic Resource
    Electronic Resource
    High-energy and high-current hydrogen negative-ion beam production with an external-filter-type large negative-ion source : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1021-1023 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large hydrogen negative-ion source with an external magnetic filter has been developed for a neutral beam injection (NBI) system in the Large Helical Device (LHD), and a high-energy and high-current H− ion beam has been produced. The ion source is operated at a high arc efficiency of 0.1 A/kW at an operational gas pressure of less than 3.5 mTorr, and produces 47 keV–16.2 A of a H− ion beam from a grid area of 25 cm×50 cm. With two-stage acceleration, 13.6 A of a H− ion beam has been successfully accelerated to 125 keV. Multibeamlet focusing by the aperture displacement technique has been achieved 11.2 m downstream with a gross divergence angle of 9 mrad. The alternate beamlet deflection by the magnetic field at the extraction grid, which results in beam broadening in the deflection direction, was well compensated also by the aperture displacement technique. These results satisfy the specification of the negative-ion-based LHD–NBI system. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146744
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  • 14
    Electronic Resource
    Electronic Resource
    Development and energy calibration of Si-FNA for LHD fast ion measurement : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 788-791 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A Si-FNA (silicon-diode-based fast neutral analyzer) was newly developed at NIFS, which uses an electrically cooled silicon-diode as an energy analyzer. Si-FNA is suitable for energy-resolved profile measurements of fast neutrals since it is compact and inexpensive. Two Si-FNAs were recently designed and installed on the Large Helical Device (LHD) during the experimental campaign of 1999. The basic performance of a Si-FNA was examined by using x/γ-ray sources of 57Co and 241Am. An energy resolution of about 3.5 keV was achieved for optimum shaping times and a resolution of about 6 keV was achieved for shorter shaping times which allowed for the higher counting rates required for LHD. The energy calibration for fast neutrals was performed by injecting neutral beams (NB) into the LHD vessel without target plasmas present. An energy loss of about 37 keV and an energy broadening of about 4.5 keV were observed at the calibration. Excellent slowing-down energy spectra are obtained for NB-injected fast particles without any influences of x/γ-rays. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1326007
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  • 15
    Electronic Resource
    Electronic Resource
    Negative hydrogen ion source development for large helical device neutral beam injector (invited) : The 8th international conference on ion sources (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1225-1230 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Large-scaled hydrogen negative ion source development is reviewed for a negative ion based neutral beam injector (NBI) in the large helical device (LHD) fusion machine. The target performance of the ion source is characterized by a high current of 30–40 A with a relatively low energy of 120–180 keV. A series of negative ion source development is conducted with a one-dimensionally reduced size of ion sources which still have a large beam area of 25 cm×26 cm or 50 cm with multi apertures. We employed a cesium-seeded volume production source with an external magnetic filter for the source development. Improvement of the arc plasma confinement is effective to produce a high-current negative ion of 16 A with a current density of 31 mA/cm2 at a low operational gas pressure below 0.4 Pa. Suppression of the accelerated electrons is achieved both by strengthening the magnetic field at the extraction grid and by shaping the inside of the extraction grid aperture to shield the secondary electrons against the acceleration electric field. Multi beamlets delivered from a large area are finely focused with the aperture displacement technique applied to the grounded grid. Based on these results, the LHD-NBI negative ion source was designed and fabricated with a beam area of 25 cm×125 cm. The LHD-NBI source produced 25 A of negative ions with an energy of 104 keV at a low gas pressure of 0.3 Pa. A long-pulse negative ion beam of 81 keV–1.3 MW was produced for 10 s. Four sources were installed to the LHD-NBI system, and around 4 MW of neutral beams were injected into the LHD plasmas with an energy of 100–110 keV in the first period for the NBI experiments. The LHD-NBI ion source is still being developed to improve its performance, and the key issues for the improvement are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150433
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  • 16
    Electronic Resource
    Electronic Resource
    H− ion source using a localized virtual magnetic filter in the plasma electrode: Type-I localized virtual magnetic filter : The 8th international conference on ion sources (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 693-695 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new multi-cusp H− ion source using a localized virtual magnetic filter of type I in the plasma electrode is investigated. A multi-pole arrangement with a spacing of 10 mm of the magnet bars holds an extraction hole, optimizing the efficient production of high H− current, and at the same time only a small electron component was co-extracted with the H− ions. The local filter arrangement separates the beam electrons at a low energy. It is shown that the coextracted total electron current is determined principally by the integrated magnetic field flux (Gcm) of the local filter with an extraction system at a constant extraction voltage. When the value of the Gcm is increased, the total electron component is reduced, while the H− electrical efficiency had a broad maximum around the optimized value of the Gcm. A thicker plasma electrode should be necessary for sufficient reduction of electron current. In pure hydrogen operation, the achieved current density of H− is 10 mA/cm2. When Cs is seeded in a filter optimized for pure volume mode H− production, the maximum H− current density obtained is 51 mA/cm2 and the ratio Iele/H− is ∼0.4 without applying a bias potential. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150263
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  • 17
    Electronic Resource
    Electronic Resource
    Simple emittance measurement of H− beams for neutral beam injectors in magnetic fusion (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 2534-2537 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel emittance meter is developed using the pepper-pot method. Kapton foils are used to detect intensity distributions of small beamlets at the "image'' plane of the pepperpot. Emittance of H− beams for the neutral beam injector of the large helical device has been measured. The normalized emittance (95%) of a 6 mA H− beam with an emission current density of about 10 mA/cm2 is ∼0.59 mm mrad. The present system is simple, and it eliminates many complexities of the existing schemes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147207
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  • 18
    Electronic Resource
    Electronic Resource
    A 100 keV operation of a large vacuum-immersed H− ion source : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1029-1031 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large vacuum-immersed H− ion source has been operated on the negative-ion-based neutral beam teststand. The achieved level of the beam and the pulse duration in beam conditioning were limited by a high-voltage breakdown in the vacuum vessel. A baffle plate at grounded potential for shielding completely from the charged particles was successful. A beam with an energy of up to 102 keV and the H− ion current of 0.55 A were achieved for 0.29 s without the breakdown. The ion current of ∼1.5 A was accelerated in cesium-seeded operation. The corresponding ion current density was ∼7 mA/cm2. A magnetic filter (as Type I LV magnetic filter) on the plasma electrode was applied. The electron beam component which was extracted from the plasma source together with H− ions was found to be very reduced. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146747
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  • 19
    Electronic Resource
    Electronic Resource
    Energetic negative ion source for fusion at NIFS (invited) (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1114-1119 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Large high current hydrogen negative ion sources have been developed for the negative ion based neutral beam injector of the Large Helical Device (LHD) at NIFS. The prototype of the negative ion source is required to deliver a negative ion beam of 45 A at the beam energy of 125 keV. The optimization of 1/3 scale ion sources which are multicusp ion source with a rod and an external magnetic filter, respectively, has been investigated for the operation parameter of the plasma source. A total H− current of 16 A is extracted at an operating pressure of 0.9–0.45 Pa with Cs seeding operation. Negative hydrogen ion current is proportional to the input arc power and a beam current density of 45 mA/cm2 is attained. The beam extraction and acceleration characteristics are studied for a single-stage and a two-stage acceleration electrode. A beam divergence angle of 5 mrad is obtained. The results of research and development of a hydrogen negative ion source at NIFS will be reviewed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146854
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  • 20
    Electronic Resource
    Electronic Resource
    Development of an intense negative hydrogen ion source with an external magnetic filter (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2541-2546 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An intense negative hydrogen ion source has been developed, which has a strong external magnetic filter field in the wide area of 35 cm×62 cm produced by a pair of permanent magnet rows located at 35.4 cm separation. The filter strength is 70 G in the center and the line-integrated filter strength is 850 G cm, which keeps the low electron temperature in the extraction region. Strong cusp magnetic field, 1.8 kG on the chamber surface, is generated for improvement of the plasma confinement. These resulted in the high arc efficiency at the low operational gas pressure. 16.2 A of H− ion current with the energy of 47 keV was obtained at the arc efficiency of 0.1 A/kW at the gas pressure of 3.8 mTorr in the cesium-mode operation. The magnetic field in the extraction gap is also strong, 450 G, for the electron suppression. The ratio of the extraction current to the negative ion current was less than 2.2 at the gas pressure of 3 mTorr. The two-stage acceleration was tested, and 13.6 A of H− ion beam was accelerated to 125 keV. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145655
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