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  • 1
    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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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Large ion yields in hydrogen scattering from a graphite surface (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6390-6396 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we report on surface scattering experiments at graphite as to model the interactions at divertor surfaces in tokamaks and conversion electrodes in negative ion sources. The formation of negative and positive hydrogen ions on a graphite surface during positive hydrogenous ion scattering at a projectile energy of 400 eV is observed. A remarkably high H− and H+ ion fraction, both varying between 10% and 30% of all scattered particles, is found during scattering of positive hydrogenous ions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364419
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  • 4
    Electronic Resource
    Electronic Resource
    Formation of positive radial electric field by electron cyclotron heating in compact helical system (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3400-3406 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The radial electric field is driven to positive value by off-axis second harmonic electron cyclotron heating (ECH) in the Compact Helical System [Plasma Physics and Controlled Nuclear Fusion Research 1988, Nice (International Atomic Energy Agency, Vienna, 1989), Vol. II, p. 411]. The observed positive electric field is associated with the outward particle flux enhanced with ECH. The enhanced particle flux triggered by the production of the electrons accelerated perpendicularly to the magnetic field with ECH results in the change of the electric field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870488
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  • 5
    Electronic Resource
    Electronic Resource
    Large current negative hydrogen ion beam production (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2813-2815 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Large current negative hydrogen ions are extracted from a multicusp ion source with an extraction area of 25×44 cm2. By seeding a small amount of cesium vapor into a source chamber, the H− current is enhanced to several times larger than that in a pure hydrogen discharge, accompanied by a reduction of the electron current and the filling gas pressure. A H− current up to 16 A is obtained with a beam energy of 40 keV from 560 extraction holes of 9 mm in diameter each, where the current density is 45 mA/cm2. The H− current increases linearly with the input arc power.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870519
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  • 6
    Electronic Resource
    Electronic Resource
    Observation of loss boundaries and ion flux spectra of end-loss ions in the tandem mirror GAMMA 10 (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 3823-3826 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Loss boundaries and ion flux spectra of end-loss ions have been observed by means of a new diagnostic device in the tandem mirror GAMMA 10 [Nucl. Fusion Suppl. 1, 429 (1983)]. In consequence of measuring simultaneously both the pitch angle profile and energy of the end-loss ions, the loss boundaries were directly ascertained to be composed of two hyperbolic lines characterized by the electrostatic plug potential in the velocity space, and also high outer mirror throat potential was found. The flux spectra were compared with the two types of theoretical results, and discussed from a viewpoint of Coulomb collision.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860338
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  • 7
    Electronic Resource
    Electronic Resource
    Initial long-pulse plasma heating at reduced power with negative-ion-based neutral beam injector in large helical device (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 4260-4265 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have achieved long-pulse plasma heating using a negative-ion-based neutral beam injector (NBI) in the large helical device (LHD), where the confinement magnetic field is generated by only external superconducting coils. In the initial long-pulse experiments at lower power than that in short-pulse experiments, 80 keV–1.1 MW NBI heating lasted for 10 s with a little increase in the plasma density at the pulse end. Almost steady-state plasma heating was achieved for 21 s with 66 keV–0.6 MW NB injection. Plasma relaxation oscillation phenomena at a period of 1–2 s were also observed for 20 s. Above 1 keV plasma was easily sustained with a long-pulse NBI heating in LHD, without the current drive nor the disruption in tokamaks. Negative ion source operation was stable and the cooling water temperature rise of beam accelerator grids was nearly saturated with a temperature rise below 10 °C. For a higher power injection, the pulse duration is determined by the beam blocking, where the reionization loss is exponentially increased together with an increase in outgas in the injection port. The port conditioning by a careful repetition of injection is effective to the extension of the injection duration and the plasma maintenance duration. The initial long-pulse NBI heating at the reduced power has demonstrated an ability of steady-state operation in superconducting LHD. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150063
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  • 8
    Electronic Resource
    Electronic Resource
    Suppression of accelerated electrons in a high-current large negative ion source (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2003-2011 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Accelerated electrons, which would lead to high thermal load of grids, have been suppressed in a high-current large hydrogen negative ion source. An extraction grid, with apertures shaped as the secondary electrons generated on the grid aperture surface would be shielded against the acceleration electric field, works well to prevent the secondary electrons from leaking to the acceleration gap, compared with a straight aperture extraction grid. Although the strong magnetic field at the extraction grid also lowers the electron leakage downstream, the aperture shaping of the extraction grid is more effective for the suppression of the accelerated electrons. The acceleration efficiency, defined by the ratio of the negative-ion current to the acceleration drain current, is improved to around 85%. There remains the accelerated electrons generated in the negative ion neutralization by collision with the residual neutral molecules during the acceleration. The direct interception of the accelerated negative ions with the downstream grid is small. The reduction of the operational gas pressure is quite important to achieve further improvement of the acceleration efficiency. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148088
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  • 9
    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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  • 10
    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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