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  • 1
    Electronic Resource
    Electronic Resource
    Improvement of a large negative ion source for the Large Helical Device neutral beam injector : Papers from the Ninth International Conference on Ion Sources (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1087-1089 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For compensation of the magnetically deflected beamlets, a new type of grid system has been applied to a large negative ion source of a negative-ion-based neutral beam injector in the Large Helical Device (LHD) fusion experimental machine. Corresponding to deviation of the negative ion beamlet trajectory due to the electron suppression magnetic field at the extraction grid, the exit aperture of the extraction grid is displaced to cancel the beamlet deflection by electrostatic lens effect. As a result, the beamlet deflection was suppressed less than 2 mrad in a wide range of energy of 110–180 keV, and the port-through efficiency of the injected beam was improved to 90%–95% from 70%–75% in the case of the previous compensation by the grounded grid aperture displacement. The injected beam power was increased to 3.5 MW with an energy of 165 keV using one injector. To improve beam uniformity of the large area beam, individual arc currents through filaments are controlled for uniform plasma production, with independent 12 arc power supplies connected to 12 filament power supplies. The initial results show good controllability of the individual arc current distribution at a high arc power. The improvement of the ion source performance would lead to an increase in the injection power in the following LHD experimental campaign. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1430528
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    In situ calibration of neutral beam port-through power and estimation of neutral beam deposition on LHD : 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. 590-593 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The neutral beam (NB) shine-through profile is routinely monitored on the Large Helical Device (LHD) both to calibrate the port-through power of the NB and to evaluate the NB-deposition power to LHD plasmas. The profile is measured with a calorimeter (CM) array on an armor plate of the NB counter wall inside the LHD vacuum vessel. An infrared camera is also used to check the beam profile where CMs are not located, and measures a temperature increase of the armor plate due to the NB heat load. The measured beam profile is compared to the calculated NB profile at the armor plate. The measurement indicates that the beam is not uniform at the exit of the ion source and that the steering angle of the beam in the horizontal direction is not the same as the designed value. It is found that the monitoring of the NB shine-through profile is important to estimate the NB port-through power and the NB deposition power, especially when the neutral beam injector (NBI) is based on a large negative-hydrogen ion source. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319867
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  • 4
    Electronic Resource
    Electronic Resource
    Development of fast response calorimeter for neutral beam shine-through measurement on CHS : 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. 586-589 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A fast response calorimeter has been developed for the neutral-beam (NB) shine-through measurement. This calorimeter has the following advantages. (1) Temporal variation of the heat load onto the calorimeter can be measured. (2) Measurement under the relatively high heat flux environment is possible. (3) The calorimetric measurement under continuous and steady-state heat load environment is also possible. The verification of the measurement principle was done using an NB-injection system on the compact helical system (CHS) at the National Institute for Fusion Science (NIFS). The measured NB power densities are compared to the power densities being evaluated by the CHS-NB profile database. It was experimentally confirmed that the time constant of the measurement is about 7 ms. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1324740
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  • 5
    Electronic Resource
    Electronic Resource
    Optimization of Cs deposition in the 1/3 scale hydrogen negative ion source for the large helical device-neutral beam injection system : The 8th interntaional conference on ion sources (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1379-1384 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact cesium deposition system was used for direct deposition of cesium atoms and ions onto the inner surface of the 1/3 scale hydrogen negative ion source for the large helical device-neutral beam injection (LHD-NBI), system. A small, well defined amount of cesium deposition in the range of 3–200 mg was tested. Negative ion extraction and acceleration were carried out both in the pure hydrogen operation mode and in the cesium mode. Single Cs deposition of 3–30 mg to the plasma chamber has produced temporary 2–5 times increases of H− yield, but the yield was decreased within several discharge pulses to the previous steady-state value. Two consecutive 30 mg depositions done within a 3–5 h/60 shot interval, produced a similar temporary increase of H− beam, but reached a large H− yield steady-state value. Deposition of larger 0.1–0.2 g Cs portions with a 20–120 h/150–270 shot interval improved the H− yield for a long (2–5 days) period of operation. Directed depositions of Cs to the various walls of the plasma chamber showed approximately the same H− increase. Deposition of 0.13 g Cs to a surface polluted by a water leak, produced a temporary increase, and a H− steady-state level similar to that from a single 30 mg cesium deposition. Deposition of 0.1 g with a cesium plasma produced one half the H− yield obtained by deposition of the same amount of cesium atoms. A higher steady-state H− current value and a smaller rate of H− yield decrease was recorded during the eight filament discharge operation, as compared to the 12 filament operation at the same discharge power. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150449
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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    A large negative-ion source immersed in the vacuum vessel on the NBI test stand at the NIFS : Proceedings of the 5th international conference on ion sources (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 1192-1194 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: To develop the powerful negative-ion-based neutral beam injection system for the large helical device, a 1/3 scaled H− source has been tested, which is immersed in the vacuum vessel. Intrinsic features of the vacuum-immersed large H− source are described. Plasma density of higher than about 1012 e/cm3 is produced. During the beam extraction, it was found that a beam-induced thin plasma exists in the vacuum vessel. In order to get a long pulse beam, this plasma was shielded and then the beam conditioning was completed up to the total beam energy of 70 keV for 100 ms, with the arc power up to about 50 kW. It is confirmed that H− current scaling as well as the plasma parameters would be similar to the scaling which is achieved by the previous 1/3 source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145054
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  • 9
    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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  • 10
    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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