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M Kisaki,
K Tsumori,
H Nakano,
K Ikeda,
M Osakabe,
K Nagaoka, M Shibuya,
M Sato,
H Sekiguchi,
S Komada,
T Kondo,
H Hayashi,
E Asano,
Y Takeiri,
O Kaneko
[show abstract]
[hide abstract]
ABSTRACT: Electron density measurements of a large-scaled negative ion source were carried out with a surface wave probe. By comparison of the electron densities determined with the surface wave probe and a Langmuir probe, it was confirmed that the surface wave probe is highly available for diagnostic of the electron density in H(-) ion sources. In addition, it was found that the ratio of the electron density to the H(-) ion density dramatically decreases with increase of a bias voltage and the H(-) ions become dominant negative particles at the bias voltage of more than 6 V.
The Review of scientific instruments 02/2012; 83(2):02B113. · 1.52 Impact Factor
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K Tsumori,
H Nakano,
M Kisaki,
K Ikeda,
K Nagaoka,
M Osakabe,
Y Takeiri,
O Kaneko, M Shibuya,
E Asano,
T Kondo,
M Sato,
S Komada,
H Sekiguchi,
N Kameyama,
T Fukuyama,
S Wada,
A Hatayama
[show abstract]
[hide abstract]
ABSTRACT: We report on the characteristics of the electronegative plasma in a large-scale hydrogen negative ion (H(-)) source. The measurement has been made with a time-resolved Langmuir probe installed in the beam extraction region. The H(-) density is monitored with a cavity ring-down system to identify the electrons in the negative charges. The electron-saturation current decreases rapidly after starting to seed Cs, and ion-ion plasma is observed in the extraction region. The H(-) density steps down during the beam extraction and the electron density jumps up correspondingly. The time integral of the decreasing H(-) charge density agrees well with the electron charge collected with the probe. The agreement of the charges is interpreted to indicate that the H(-) density decreasing at the beam extraction is compensated by the electrons diffusing from the driver region. In the plasmas with very low electron density, the pre-sheath of the extraction field penetrates deeply inside the plasmas. That is because the shielding length in those plasmas is longer than that in the usual electron-ion plasmas, and furthermore the electrons are suppressed to diffuse to the extraction region due to the strong magnetic field.
The Review of scientific instruments 02/2012; 83(2):02B116. · 1.52 Impact Factor
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H Nakano,
M Osakabe,
K Tsumori,
M Sato, M Shibuya,
K Ikeda,
K Nagaoka,
O Kaneko,
E Asano,
T Kondo,
S Komada,
Y Takeiri
[show abstract]
[hide abstract]
ABSTRACT: An additional beamline, BL5, equipped with four positive ion sources will be installed on Large Helical Device (LHD) in 2010. The performance of an ion source which generates 80 keV deuterium and 60 keV hydrogen beams was investigated. The structure of the ion source is based on that of a BL4 ion source on LHD. The main differences between the ion sources for the BL4 and BL5 are the acceleration voltages and the materials of plasma electrodes: copper and molybdenum, respectively. The molybdenum plasma electrode for BL5 has better performance than the copper plasma electrode of BL4. The integrated performance of the ion source for BL5 reached a value equivalent to approximately 58 A in the beam current of hydrogen positive ion at 60 keV in the beam energy.
The Review of scientific instruments 02/2010; 81(2):02B116. · 1.52 Impact Factor
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K Tsumori,
M Osakabe,
Y Takeiri,
O Kaneko,
K Nagaoka,
K Ikeda,
H Nakano,
Y Oka, M Shibuya,
E Asano,
S Komada,
T Kondo,
M Sato
[show abstract]
[hide abstract]
ABSTRACT: Characteristics of multibeamlets are investigated by means of beamlet monitoring technique. The beamlets are extracted from an accelerator with multislot grounded grid and the profiles are observed as infrared images of temperature distributions on a cold isostatic pressed graphite plate exposed by H-beamlets. The optimal horizontal and vertical divergence angles of single beamlet are estimated at 4.1 and 6.1 mrad, respectively.
The Review of scientific instruments 02/2010; 81(2):02B117. · 1.52 Impact Factor
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K Tsumori,
M Osakabe,
O Kaneko,
Y Takeiri,
K Nagaoka,
Y Oka,
K Ikeda, M Shibuya,
E Asano,
S Komada,
T Kondo,
M Sato
[show abstract]
[hide abstract]
ABSTRACT: The beam profiles, port-through, rates and injection powers obtained with an improved accelerator with the multislot grounded grid are described. The accelerator has a combination of a steering grid with racetrack shaped aperture and multislot grounded grid to improve the beam optics. The optimal beam optics is obtained at the voltage ratio of 16.5-16.8, and the profiles are well fit by superposing multibeamlets with the divergent angles of 5.0 and 7.2 mrad along the direction parallel to the long and short axes of the slots of grounded grid. By adopting the racetrack shaped steering grid, the port-through rate increases from 34% to 38%, and the maximum injection power reaches 6 MW/187 keV.
Review of Scientific Instruments 03/2008; 79(2 Pt 2):02C107. · 1.37 Impact Factor
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Y Oka,
K Tsumori,
K Ikeda,
O Kaneko,
K Nagaoka,
M Osakabe,
Y Takeiri,
E Asano,
S Komada,
T Kondo,
M Sato, M Shibuya,
L R Grisham,
Y Ikeda,
M Hanada,
N Umeda
[show abstract]
[hide abstract]
ABSTRACT: In the large area negative ion source for the LHD negative-ion-(H(-))-based neutral beam system, (I) we used the spectrometer to measure caesium lines in the source plasma during beam shots. (II) With Doppler-shifted measurements, the H(alpha) line at three different locations along the beam as well as the spectrum profile for cases of different plasma grid areas. (III) Caesium deposition monitor with a high speed shutter was tested to measure the weight of the deposited Cs layer. In the observation, cleaner spectra of Doppler-shifted H(alpha) line with only a small level of background light were obtained at a new observation port which viewed the blueshifted light in the drift region after the accelerator of a LHD ion source. Both the amounts of Cs I (852 nm, neutral Cs(0)) and Cs II (522 nm, Cs(+)) in the source plasma light rose sharply when beam acceleration began, and continued rising during a 10 s pulse. It was thought that this was because the cesium was evaporated/sputtered from the source back plate by the back-streaming positive ions. Cs deposition rate to the crystal sensor measured by adjusting the shutter open time was evaluated to be 2.9 nanograms/s cm(2) for preliminary testing. More neutral Cs tended to be evolved in the source after arc discharge. Much Cs could be consumed in a high rate-pulsed operation (such as LHD source).
Review of Scientific Instruments 03/2008; 79(2 Pt 2):02C105. · 1.37 Impact Factor
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K Tsumori,
Y Takeiri,
K Nagaoka,
K Ikeda,
M Osakabe,
Y Oka,
O Kaneko, M Shibuya,
T Kondo,
M Sato,
E Asano
[show abstract]
[hide abstract]
ABSTRACT: The results on high power injection with the neutral beam injection (NBI) system for the Large Helical Device (LHD) are reported. The system consists of three beam-lines with two hydrogen negative ion (H− ion) sources installed in each beam-line. In order to improve the injection power, a new beam accelerator with a multi-slot grounded grid (MSGG) has been developed and applied to one beam-line. Using the accelerator, a maximum power of 5.7 MW was achieved in 2003 and 2004, and the maximum energy of 189 keV was reached. The power and energy exceeded the design values of the individual beam-line for LHD. The other beam-lines also increased their injection power up to about 4 MW, and the total injection power of 13.1 MW was achieved with three beam-lines in 2003. Although the accelerator had an advantage in high power beam injection, extracted beams expand in the short side direction of the ground-grid slot. The disadvantage has been resolved by modifying the aperture shapes of the steering grid.
Plasma Science and Technology 04/2006; 8(1):24. · 0.41 Impact Factor
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Y. Oka,
K. Ikeda,
Y. Takeiri,
K. Tsumori,
O. Kaneko,
K. Nagaoka,
M. Osakabe,
E. Asano,
T. Kondo,
M. Sato, M. Shibuya,
L. Grisham,
N. Umeda,
A. Honda,
Y. Ikeda,
T. Yamamoto
[show abstract]
[hide abstract]
ABSTRACT: The velocity spectra of the negative-ion-(H−) based neutral beams are studied in high-performance large-area ion sources during injection into large helical device fusion plasmas. We are conducting systematic observations in standard neutral beam injection to correlate beam spectra with source operating conditions. Almost all of the transmitted beam power was at full acceleration energy ( ∼ 170 keV). The small stripping beam component which was produced in the extraction gap was evaluated to be about 9%–22% by amplitude of the measured spectra for the sources in beam lines 1 and 2. H− production uniformity from the spectrum profile was 86%–90% for three sources. For the longest pulse injection during 74 and 128 s, a full energy component tended to decrease with time, while the accelerator gap stripping tail tended to increase slightly with time, which is attributed to beam-induced outgassing in the accelerator. A higher conductance multislot ground grid accelerator appeared to show little growth in the accelerator gap beam stripping during long pulses compared to the conventional multiaperture ground grid. The beam uniformity appeared to vary in part with the Cs uniformity on the plasma grid.
Review of Scientific Instruments 03/2006; 77(3):03A538-03A538-4. · 1.37 Impact Factor
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Y. Oka,
K. Ikeda,
O. Kaneko,
K. Nagaoka,
M. Osakabe,
Y. Takeiri,
K. Tsumori,
E. Asano,
T. Kondo,
M. Sato, M. Shibuya,
T. Shoji
[show abstract]
[hide abstract]
ABSTRACT: A new multiantenna system for large area radio-frequency H− ion source using a filamentless ion source was tested to extract ions from dense plasmas with high rf input power. A 1/6 scale large helical device ion source was equipped inside a plasma chamber with four linear antenna rods. Positive-ion extraction with a single hole extractor was studied in detail, while a negative one only showed preliminary results. The positive-ion current density of 34 mA/cm2 to the collector plate was achieved with a new multiantenna after optimization of the antenna number and source gas pressure, where the number of the antennae was 2 with ∼ 36 kW of rf input power and with a gas pressure of ∼ 0.1 Pa with H2. If the external magnetic filter optimized for negative-ion production in the multifilament discharge source is taken off, the current density is estimated to reach about 120 mA/cm2. This corresponded closely to the value measured with a Langmuir probe near the center. Two antennae appear to be required to generate uniform plasmas as well as dense plasmas in the present size of the 35×35 cm2 source. A negative-ion current density of 0.3 mA/cm2 to the collector plate was detected with hydrogen without optimization. This multiantenna rf ion source is expected to be adaptable advantageously to large area positive- and negative-ion sources, owing to not only a filamentless source but also potentially due to uniform plasmas as well as probable low-electron-temperature plasmas, compared to that with a one-turn coil system.
Review of Scientific Instruments 03/2006; 77(3):03B506-03B506-3. · 1.37 Impact Factor
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Y Takeiri,
K Tsumori,
K Ikeda,
M Osakabe,
K Nagaoka,
Y Oka,
E Asano,
T Kondo,
M Sato, M Shibuya,
S Komada,
O Kaneko
[show abstract]
[hide abstract]
ABSTRACT: The negative-ion-based neutral beam injectors (negative-NBIs) have been operated for 10 years in Large Helical Device (LHD), which is the world's largest superconducting fusion-experimental machine. The LHD is equipped with three negative-NBIs, the injection energy of which is 180keV with hydrogen beams [1,2]. The injection power has been increased year by year and achieved to 15MW with three injectors, due to the successive improvement of the negative ion sources. The ion sources produce high-current negative ions of more than 30A, corresponding to 30mA/cm 2 of the current density. Improvement of the voltage holding ability in the beam acceleration mainly contributes to the increase in the negative-ion beam power. As well as the multi-slotted grounded grid (GG) [3], enlargement of the round aperture of the GG is effective to raising the acceleration voltage. Higher transparency of the GG results in the reduction of the heat load of GG, which should contribute to the rise in the acceleration voltage. Reduction of the co-accelerated electrons is also important to the improvement of the voltage holding. The steering grid (SG), located just downstream the extraction grid (EG), plays a role in preventing the secondary electron generated inside the EG aperture from entering the acceleration gap. The combination of the shape of SG and EG apertures has an influence on the amount of the electron acceleration, and the reduction of the accelerated electrons leads to the improvement of the voltage holding. The Cs consumption rate is a concern for a long-period operation. Higher-current H -production needs higher arc discharges, and the evaporation of tungsten filaments is enhanced. Proportional to the tungsten evaporation, the Cs consumption is observed to increase. Related to the Cs recycling, the optical emission spectroscopy is applied to the measurement of the Cs distribution in the arc chamber [4]. Along a line of sight parallel to the magnetic filter field near the plasma grid, an increase in the neutral Cs is observed during the beam extraction. Recent progress in the negative-NBIs in LHD is overviewed, highlighted to the improved performance of the high-power negative ion sources.
Nucl. Fusion AIP Conference Proceedings Rev. Sci. Instrum. Rev. Sci. Instrum. 01/2006; 4634(79):199-211.
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Y Oka,
K Ikeda,
Y. Takeiri,
K. Tsumori,
O. Kaneko,
K. Nagaoka,
M. Osakabe,
E. Asano,
S Komada,
T Kondo,
M Sato, M Shibuya,
L. Grisham,
N Umeda,
A Honda
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Y. Takeiri,
O. Kaneko,
Y Oka,
K. Tsumori,
K Ikeda,
K. Nagaoka,
E. Asano,
M Sato, M Shibuya,
S Komada,
M. Osakabe,
T Kondo
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Y. Takeiri,
O. Kaneko,
Y Oka,
K. Tsumori,
M. Osakabe,
K Ikeda,
K. Nagaoka,
E. Asano,
T Kondo,
M Sato, M Shibuya,
S Komada
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K. Tsumori,
K. Nagaoka,
M. Osakabe,
K Ikeda,
Y. Takeiri,
O. Kaneko,
Y Oka, M Shibuya,
E. Asano,
M Sato,
T Kondo,
S Asano,
J Watanabe,
Y Suzuki,
K Ichihashi,
T Okuyama
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Y Oka,
L. Grisham,
N Umeda,
K Ikeda,
Y. Takeiri,
K. Tsumori,
A Honda,
Y Ikeda,
O. Kaneko,
K. Nagaoka,
M. Osakabe,
T Yamamoto,
E. Asano,
T Kondo,
M Sato, M Shibuya
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Y. Takeiri,
O. Kaneko,
K. Tsumori,
M. Osakabe,
K Ikeda,
K. Nagaoka,
H Nakano,
E. Asano,
T Kondo,
M Sato, M Shibuya,
S Komada
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Y. Takeiri,
K. Tsumori,
M. Osakabe,
K Ikeda,
K. Nagaoka,
H Nakano,
E. Asano,
T Kondo,
M Sato, M Shibuya,
S Komada,
O. Kaneko
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K. Tsumori,
M. Osakabe,
O. Kaneko,
Y. Takeiri,
K. Nagaoka,
K Ikeda,
H Nakano, M Shibuya,
E. Asano,
M Sato,
T Kondo,
S Komada
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H Nakano,
K. Tsumori,
K. Nagaoka, M Shibuya,
K Ikeda,
M. Osakabe,
O. Kaneko,
E. Asano,
T Kondo,
M Sato,
S Komada,
Y. Takeiri
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Y. Takeiri,
K Ikeda,
Y Oka,
K. Tsumori,
M. Osakabe,
K. Nagaoka,
O. Kaneko,
E. Asano,
T Kondo,
M Sato, M Shibuya,
S Komada
[show abstract]
[hide abstract]
ABSTRACT: The injection duration has been extended beyond 100 s with a high-power hydrogen negative-ion source in a negative-ion-based neutral beam injector of the Large Helical Device superconducting fusion machine. The ion source is a cesium-seeded source with a thermally insulated plasma grid (PG), and optimized for a short-pulse operation of 2–3 s. The negative-ion production efficiency is strongly dependent on the PG temperature, and in the long-pulse operation it exceeds an appropriate temperature range of 200–300 °C, at which the optimum cesium coverage is formed on the PG surface. By making the PG temperature rise slower with a reduced arc power, the injection duration was extended to 110 s with an injection power of 110 kW. To extend the injection duration further with a higher injection power, stainless-steel cooling tubes have been mechanically attached to the PG for suppression of the PG temperature rise in the long-pulse operation. As a result, a long-pulse injection with an injection power of 200 kW was extended to 128 s until it was manually stopped due to the plasma collapse. However, the beam duration could be limited to around 3 min because the PG temperature rise was not saturated due to a low thermal conductivity with the thickness of the stainless-steel tube determined so that the short-pulse operation is also possible. On the other hand, the longitudinal beam distribution in a grid area of 25×125 cm^2 is observed to be more uniform than that with the uncooled PG. The temperature distribution of the individual grid parts becomes more uniform with the cooled PG, which should contribute to the improvement of the beam uniformity.
