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M. Hanada - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the beam halo in Negative Ion sources by using 3d3v pic code
    Review of Scientific Instruments, 2016
    Co-Authors: K Miyamoto, M. Hanada, Akiyoshi Hatayama, A Kojima, S Nishioka, I Goto, J Hiratsuka
    Abstract:

    The physical mechanism of the formatIon of the Negative Ion beam halo and the heat loads of the multi-stage acceleratIon grids are investigated with the 3D PIC (particle in cell) simulatIon. The following physical mechanism of the beam halo formatIon is verified: The beam core and the halo consist of the Negative Ions extracted from the center and the periphery of the meniscus, respectively. This difference of Negative Ion extractIon locatIon results in a geometrical aberratIon. Furthermore, it is shown that the heat loads on the first acceleratIon grid and the second acceleratIon grid are quantitatively improved compared with those for the 2D PIC simulatIon result.

  • 22 a beam productIon of the uniform Negative Ions in the jt 60 Negative Ion source
    Fusion Engineering and Design, 2015
    Co-Authors: Masafumi Yoshida, M Kashiwagi, M. Hanada, Akiyoshi Hatayama, L. R. Grisham, N. Akino, A Kojima, T Shibata, Takashi Yamamoto, Y. Endo
    Abstract:

    Abstract In order to improve the spatial uniformity of the Negative Ion beam and to produce high current Negative Ion beams in a large Negative Ion source, a magnetic field configuratIon is modified from an original transverse filter to a tent-shaped filter, in combinatIon with reducing the magnetic field strength in the JT-60 Negative Ion source. As a result, the beam uniformity is improved from 68% to 83% over an area of the whole extractIon area of 450 × 1100 mm 2 . The improvement of the beam uniformity leads to the productIon of 32 A H − Ion beams with the whole extractIon area. The obtained beam current fulfills the requirement for JT-60SA.

  • progress in long pulse productIon of powerful Negative Ion beams for jt 60sa and iter
    Nuclear Fusion, 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, N. Akino, M. Komata, M Yoshida, N Umeda, K. Mogaki
    Abstract:

    Significant progress in the extensIon of pulse duratIons of powerful Negative Ion beams has been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long-pulse productIon/acceleratIon of Negative Ion beams in JT-60SA and ITER, new technologies have been developed in the JT-60SA Ion source and the MeV accelerator in Japan Atomic Energy Agency.As for the long-pulse productIon of high-current Negative Ions for the JT-60SA Ion source, the pulse duratIons have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA Ion source, which satisfies the required pulse duratIon of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform Negative Ion productIons with the modified tent-shaped filter field configuratIon. Moreover, each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER Ion source because the sustainment of the caesium coverage in the large extractIon area is one of the common issues between JT-60SA and ITER.As for the long-pulse acceleratIon of high power density beams in the MeV accelerator for ITER, the pulse duratIon of MeV-class Negative Ion beams has been extended by more than 2 orders of magnitude by modifying the extractIon grid with a high cooling capability and a high transmissIon of Negative Ions. A long-pulse acceleratIon of 60 s has been achieved at 70 MW m−2 (683 keV, 100 A m−2) which has reached the power density of JT-60SA level of 65 MW m−2. No degradatIons of the voltage holding capability of the acceleratIon voltage and the beam optics due to the distortIon of the acceleratIon grids have been observed in this power density level.These results are the longest pulse duratIons of high-current and high-power-density Negative Ion beams in the world.

  • long pulse productIon of high current Negative Ion beam by using actively temperature controlled plasma grid for jt 60sa Negative Ion source
    FOURTH INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS BEAMS AND SOURCES (NIBS 2014), 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, M Yoshida, N Umeda, J Hiratsuka, L. R. Grisham
    Abstract:

    The temperature control system of the large-size plasma grid has been developed to realize the long pulse productIon of high-current Negative Ions for JT-60SA. By using this prototype system for the JT-60SA Ion source, 15 A Negative Ions has been sustained for 100 s for the first time, which is three times longer than that obtained in JT-60U. In this system, a high-temperature fluorinated fluid with a high boiling point of 270 degree Celsius is circulated in the cooling channels of the plasma grids (PG) where a cesium (Cs) coverage is formed to enhance the Negative Ion productIon. Because the PG temperature control had been applied to only 10% of the extractIon area previously, the prototype PG with the full extractIon area (110 cm × 45 cm) was developed to increase the Negative Ion current in this time. In the preliminary results of long pulse productIons of high-current Negative Ions at a Cs conditIoning phase, the Negative Ion productIon was gradually degraded in the last half of 100 s pulse where the ...

  • achievement of 500 kev Negative Ion beam acceleratIon on jt 60u Negative Ion based neutral beam injector
    Nuclear Fusion, 2011
    Co-Authors: A Kojima, M. Hanada, N. Akino, M. Komata, K. Mogaki, M Kawai, M Kazawa, Y Tanaka, K Usui, S Sasaki
    Abstract:

    Hydrogen Negative Ion beams of 507 keV, 1 A and 486 keV, 2.8 A have been successfully produced in the JT-60U Negative Ion source with a three-stage accelerator by overcoming a poor voltage holding of the accelerator with large-size grids of ~2 m2. This is the first result of H− beam acceleratIon up to 500 keV at a high current of over 1 A. In order to improve the voltage holding capability, the breakdown voltages of the large-size grids and small-size electrodes with uniform and locally strong electric fields were examined by changing the gap length. It was found that the voltage holding of the large-size grids was below half of that of the small-size electrodes with a uniform electric field which was used in the design of the accelerator. This degradatIon was found to be caused by the local electric field concentratIons in additIon to the size. Based on the results of the voltage holding tests and beam optics calculatIons, the gap lengths of the large-size grids were tuned to have a capability to sustain 600 kV. As a result, the gap tuning realized stable voltage holding during beam acceleratIons without significant degradatIons of the beam optics and stripping loss. These results indicated that stable 500 keV beam acceleratIons required for JT-60SA are feasible and this gap tuning is also applicable for the design of ITER accelerator.

K. Watanabe - One of the best experts on this subject based on the ideXlab platform.

  • progress in long pulse productIon of powerful Negative Ion beams for jt 60sa and iter
    Nuclear Fusion, 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, N. Akino, M. Komata, M Yoshida, N Umeda, K. Mogaki
    Abstract:

    Significant progress in the extensIon of pulse duratIons of powerful Negative Ion beams has been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long-pulse productIon/acceleratIon of Negative Ion beams in JT-60SA and ITER, new technologies have been developed in the JT-60SA Ion source and the MeV accelerator in Japan Atomic Energy Agency.As for the long-pulse productIon of high-current Negative Ions for the JT-60SA Ion source, the pulse duratIons have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA Ion source, which satisfies the required pulse duratIon of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform Negative Ion productIons with the modified tent-shaped filter field configuratIon. Moreover, each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER Ion source because the sustainment of the caesium coverage in the large extractIon area is one of the common issues between JT-60SA and ITER.As for the long-pulse acceleratIon of high power density beams in the MeV accelerator for ITER, the pulse duratIon of MeV-class Negative Ion beams has been extended by more than 2 orders of magnitude by modifying the extractIon grid with a high cooling capability and a high transmissIon of Negative Ions. A long-pulse acceleratIon of 60 s has been achieved at 70 MW m−2 (683 keV, 100 A m−2) which has reached the power density of JT-60SA level of 65 MW m−2. No degradatIons of the voltage holding capability of the acceleratIon voltage and the beam optics due to the distortIon of the acceleratIon grids have been observed in this power density level.These results are the longest pulse duratIons of high-current and high-power-density Negative Ion beams in the world.

  • long pulse productIon of high current Negative Ion beam by using actively temperature controlled plasma grid for jt 60sa Negative Ion source
    FOURTH INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS BEAMS AND SOURCES (NIBS 2014), 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, M Yoshida, N Umeda, J Hiratsuka, L. R. Grisham
    Abstract:

    The temperature control system of the large-size plasma grid has been developed to realize the long pulse productIon of high-current Negative Ions for JT-60SA. By using this prototype system for the JT-60SA Ion source, 15 A Negative Ions has been sustained for 100 s for the first time, which is three times longer than that obtained in JT-60U. In this system, a high-temperature fluorinated fluid with a high boiling point of 270 degree Celsius is circulated in the cooling channels of the plasma grids (PG) where a cesium (Cs) coverage is formed to enhance the Negative Ion productIon. Because the PG temperature control had been applied to only 10% of the extractIon area previously, the prototype PG with the full extractIon area (110 cm × 45 cm) was developed to increase the Negative Ion current in this time. In the preliminary results of long pulse productIons of high-current Negative Ions at a Cs conditIoning phase, the Negative Ion productIon was gradually degraded in the last half of 100 s pulse where the ...

  • analysis of electron temperature distributIon by kinetic modeling of electron energy distributIon functIon in jaea 10 ampere Negative Ion source
    THIRD INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS BEAMS AND SOURCES (NIBS 2012), 2013
    Co-Authors: T Shibata, M Kashiwagi, M. Taniguchi, K. Watanabe, Hiroyuki Tobari, T Inoue, N Umeda, R Terasaki, M Dairaku, K Sakamto
    Abstract:

    In large Negative Ion sources of the neutral beam injector (NBI) for large fusIon devices, such as ITER and JT-60SA, one of issues is that Negative Ion beam might be partially intercepted at acceleratIon grids due to a spatial non-uniformity of Negative Ion productIon on large extractIon area. Previous experiments have shown that fast electrons emitted from filament cathodes are transported in a longitudinal directIon by B × grad B drift and the spatial distributIon of electron temperature (Te) is strongly related with the non-uniformity of Negative Ion productIon. In this study, a three-dimensIonal electron transport analysis code including detailed collisIon processes has been developed to clarify a physical mechanism of non-uniform Te distributIon. Electron density and temperature in the analysis agree well with measurements by Langmuir probe in the JAEA 10A Ion source. Then, this study has clarified that the non-uniformity of Te distributIon is mainly caused by the following reasons; i) fast electrons...

  • improvement of voltage holding capability in the 500 kev Negative Ion source for jt 60sa
    Review of Scientific Instruments, 2010
    Co-Authors: Y Tanaka, M. Hanada, M. Taniguchi, K. Watanabe, T Inoue, N. Akino, A Kojima, Tatsuo Shimizu, K Ohshima, M Kashiwagi
    Abstract:

    Voltage holding capability of JT-60 Negative Ion source that has a large electrostatic Negative Ion accelerator with 45 cm×1.1 m acceleratIon grids was experimentally examined and improved to realize 500 keV, 22 A, and 100 s D− Ion beams for JT-60 Super Advanced. The gap lengths in the acceleratIon stages were extended to reduce electric fields in a gap between the large grids and at the corner of the support flanges from the original 4–5 to 3–4 kV/mm. As a result, the voltage holding capability without beam acceleratIon has been successfully improved from 400 to 500 kV. The pulse duratIon to hold 500 kV reached 40 s of the power supply limitatIon.

  • the origin of beam non uniformity in a large cs seeded Negative Ion source
    Nuclear Fusion, 2006
    Co-Authors: M. Hanada, M Kashiwagi, Akiyoshi Hatayama, M. Taniguchi, T. Seki, Naoyuki Takado, T Inoue, T Mizuno, K Sakamoto, K. Watanabe
    Abstract:

    The origin of longitudinal beam non-uniformity, which is one of the key issues in large caesium (Cs)-seeded Negative Ion sources for fusIon applicatIon, was experimentally investigated in the JAERI 10 A Negative Ion source. A sufficient caesium was seeded in the Negative Ion source to enhance the Negative Ion productIon. The beam intensity with Cs was typically four times higher than that without Cs, and was relatively high in the upper regIon where the electron temperature and plasma density were relatively high. This distributIon was significantly different from that without Cs. From the correlatIon between the beam intensity and the plasma parameters, it was found that the beam non-uniformity was due to the localizatIon of the plasma.The front edge of the filaments was bent towards the plasma grid to suppress the plasma localizatIon. This resulted in the significant improvement of the beam uniformity. The root-mean-square deviatIon of the beam intensity from the averaged value decreased to a half of that before the modificatIon while the beam intensity integrated along the longitudinal directIon was kept constant. This result indicates that the suppressIon of the plasma localizatIon by the filament modificatIon is effective for improving the beam uniformity in the Cs-seeded Negative Ion source.

N. Akino - One of the best experts on this subject based on the ideXlab platform.

  • 22 a beam productIon of the uniform Negative Ions in the jt 60 Negative Ion source
    Fusion Engineering and Design, 2015
    Co-Authors: Masafumi Yoshida, M Kashiwagi, M. Hanada, Akiyoshi Hatayama, L. R. Grisham, N. Akino, A Kojima, T Shibata, Takashi Yamamoto, Y. Endo
    Abstract:

    Abstract In order to improve the spatial uniformity of the Negative Ion beam and to produce high current Negative Ion beams in a large Negative Ion source, a magnetic field configuratIon is modified from an original transverse filter to a tent-shaped filter, in combinatIon with reducing the magnetic field strength in the JT-60 Negative Ion source. As a result, the beam uniformity is improved from 68% to 83% over an area of the whole extractIon area of 450 × 1100 mm 2 . The improvement of the beam uniformity leads to the productIon of 32 A H − Ion beams with the whole extractIon area. The obtained beam current fulfills the requirement for JT-60SA.

  • progress in long pulse productIon of powerful Negative Ion beams for jt 60sa and iter
    Nuclear Fusion, 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, N. Akino, M. Komata, M Yoshida, N Umeda, K. Mogaki
    Abstract:

    Significant progress in the extensIon of pulse duratIons of powerful Negative Ion beams has been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long-pulse productIon/acceleratIon of Negative Ion beams in JT-60SA and ITER, new technologies have been developed in the JT-60SA Ion source and the MeV accelerator in Japan Atomic Energy Agency.As for the long-pulse productIon of high-current Negative Ions for the JT-60SA Ion source, the pulse duratIons have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA Ion source, which satisfies the required pulse duratIon of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform Negative Ion productIons with the modified tent-shaped filter field configuratIon. Moreover, each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER Ion source because the sustainment of the caesium coverage in the large extractIon area is one of the common issues between JT-60SA and ITER.As for the long-pulse acceleratIon of high power density beams in the MeV accelerator for ITER, the pulse duratIon of MeV-class Negative Ion beams has been extended by more than 2 orders of magnitude by modifying the extractIon grid with a high cooling capability and a high transmissIon of Negative Ions. A long-pulse acceleratIon of 60 s has been achieved at 70 MW m−2 (683 keV, 100 A m−2) which has reached the power density of JT-60SA level of 65 MW m−2. No degradatIons of the voltage holding capability of the acceleratIon voltage and the beam optics due to the distortIon of the acceleratIon grids have been observed in this power density level.These results are the longest pulse duratIons of high-current and high-power-density Negative Ion beams in the world.

  • Improvement of uniformity of the Negative Ion beams by tent-shaped magnetic field in the JT-60 Negative Ion source.
    Review of Scientific Instruments, 2014
    Co-Authors: Masafumi Yoshida, Mieko Kashiwagi, Masaya Hanada, Atsushi Kojima, L. R. Grisham, N. Akino, Y. Endo, M. Komata, K. Mogaki, S. Nemoto
    Abstract:

    Non-uniformity of the Negative Ion beams in the JT-60 Negative Ion source with the world-largest Ion extractIon area was improved by modifying the magnetic filter in the source from the plasma grid (PG) filter to a tent-shaped filter. The magnetic design via electron trajectory calculatIon showed that the tent-shaped filter was expected to suppress the localizatIon of the primary electrons emitted from the filaments and created uniform plasma with positive Ions and atoms of the parent particles for the Negative Ions. By modifying the magnetic filter to the tent-shaped filter, the uniformity defined as the deviatIon from the averaged beam intensity was reduced from 14% of the PG filter to ∼10% without a reductIon of the Negative Ion productIon.

  • achievement of 500 kev Negative Ion beam acceleratIon on jt 60u Negative Ion based neutral beam injector
    Nuclear Fusion, 2011
    Co-Authors: A Kojima, M. Hanada, N. Akino, M. Komata, K. Mogaki, M Kawai, M Kazawa, Y Tanaka, K Usui, S Sasaki
    Abstract:

    Hydrogen Negative Ion beams of 507 keV, 1 A and 486 keV, 2.8 A have been successfully produced in the JT-60U Negative Ion source with a three-stage accelerator by overcoming a poor voltage holding of the accelerator with large-size grids of ~2 m2. This is the first result of H− beam acceleratIon up to 500 keV at a high current of over 1 A. In order to improve the voltage holding capability, the breakdown voltages of the large-size grids and small-size electrodes with uniform and locally strong electric fields were examined by changing the gap length. It was found that the voltage holding of the large-size grids was below half of that of the small-size electrodes with a uniform electric field which was used in the design of the accelerator. This degradatIon was found to be caused by the local electric field concentratIons in additIon to the size. Based on the results of the voltage holding tests and beam optics calculatIons, the gap lengths of the large-size grids were tuned to have a capability to sustain 600 kV. As a result, the gap tuning realized stable voltage holding during beam acceleratIons without significant degradatIons of the beam optics and stripping loss. These results indicated that stable 500 keV beam acceleratIons required for JT-60SA are feasible and this gap tuning is also applicable for the design of ITER accelerator.

  • improvement of voltage holding capability in the 500 kev Negative Ion source for jt 60sa
    Review of Scientific Instruments, 2010
    Co-Authors: Y Tanaka, M. Hanada, M. Taniguchi, K. Watanabe, T Inoue, N. Akino, A Kojima, Tatsuo Shimizu, K Ohshima, M Kashiwagi
    Abstract:

    Voltage holding capability of JT-60 Negative Ion source that has a large electrostatic Negative Ion accelerator with 45 cm×1.1 m acceleratIon grids was experimentally examined and improved to realize 500 keV, 22 A, and 100 s D− Ion beams for JT-60 Super Advanced. The gap lengths in the acceleratIon stages were extended to reduce electric fields in a gap between the large grids and at the corner of the support flanges from the original 4–5 to 3–4 kV/mm. As a result, the voltage holding capability without beam acceleratIon has been successfully improved from 400 to 500 kV. The pulse duratIon to hold 500 kV reached 40 s of the power supply limitatIon.

M Kashiwagi - One of the best experts on this subject based on the ideXlab platform.

  • 22 a beam productIon of the uniform Negative Ions in the jt 60 Negative Ion source
    Fusion Engineering and Design, 2015
    Co-Authors: Masafumi Yoshida, M Kashiwagi, M. Hanada, Akiyoshi Hatayama, L. R. Grisham, N. Akino, A Kojima, T Shibata, Takashi Yamamoto, Y. Endo
    Abstract:

    Abstract In order to improve the spatial uniformity of the Negative Ion beam and to produce high current Negative Ion beams in a large Negative Ion source, a magnetic field configuratIon is modified from an original transverse filter to a tent-shaped filter, in combinatIon with reducing the magnetic field strength in the JT-60 Negative Ion source. As a result, the beam uniformity is improved from 68% to 83% over an area of the whole extractIon area of 450 × 1100 mm 2 . The improvement of the beam uniformity leads to the productIon of 32 A H − Ion beams with the whole extractIon area. The obtained beam current fulfills the requirement for JT-60SA.

  • progress in long pulse productIon of powerful Negative Ion beams for jt 60sa and iter
    Nuclear Fusion, 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, N. Akino, M. Komata, M Yoshida, N Umeda, K. Mogaki
    Abstract:

    Significant progress in the extensIon of pulse duratIons of powerful Negative Ion beams has been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long-pulse productIon/acceleratIon of Negative Ion beams in JT-60SA and ITER, new technologies have been developed in the JT-60SA Ion source and the MeV accelerator in Japan Atomic Energy Agency.As for the long-pulse productIon of high-current Negative Ions for the JT-60SA Ion source, the pulse duratIons have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA Ion source, which satisfies the required pulse duratIon of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform Negative Ion productIons with the modified tent-shaped filter field configuratIon. Moreover, each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER Ion source because the sustainment of the caesium coverage in the large extractIon area is one of the common issues between JT-60SA and ITER.As for the long-pulse acceleratIon of high power density beams in the MeV accelerator for ITER, the pulse duratIon of MeV-class Negative Ion beams has been extended by more than 2 orders of magnitude by modifying the extractIon grid with a high cooling capability and a high transmissIon of Negative Ions. A long-pulse acceleratIon of 60 s has been achieved at 70 MW m−2 (683 keV, 100 A m−2) which has reached the power density of JT-60SA level of 65 MW m−2. No degradatIons of the voltage holding capability of the acceleratIon voltage and the beam optics due to the distortIon of the acceleratIon grids have been observed in this power density level.These results are the longest pulse duratIons of high-current and high-power-density Negative Ion beams in the world.

  • long pulse productIon of high current Negative Ion beam by using actively temperature controlled plasma grid for jt 60sa Negative Ion source
    FOURTH INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS BEAMS AND SOURCES (NIBS 2014), 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, M Yoshida, N Umeda, J Hiratsuka, L. R. Grisham
    Abstract:

    The temperature control system of the large-size plasma grid has been developed to realize the long pulse productIon of high-current Negative Ions for JT-60SA. By using this prototype system for the JT-60SA Ion source, 15 A Negative Ions has been sustained for 100 s for the first time, which is three times longer than that obtained in JT-60U. In this system, a high-temperature fluorinated fluid with a high boiling point of 270 degree Celsius is circulated in the cooling channels of the plasma grids (PG) where a cesium (Cs) coverage is formed to enhance the Negative Ion productIon. Because the PG temperature control had been applied to only 10% of the extractIon area previously, the prototype PG with the full extractIon area (110 cm × 45 cm) was developed to increase the Negative Ion current in this time. In the preliminary results of long pulse productIons of high-current Negative Ions at a Cs conditIoning phase, the Negative Ion productIon was gradually degraded in the last half of 100 s pulse where the ...

  • analysis of electron temperature distributIon by kinetic modeling of electron energy distributIon functIon in jaea 10 ampere Negative Ion source
    THIRD INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS BEAMS AND SOURCES (NIBS 2012), 2013
    Co-Authors: T Shibata, M Kashiwagi, M. Taniguchi, K. Watanabe, Hiroyuki Tobari, T Inoue, N Umeda, R Terasaki, M Dairaku, K Sakamto
    Abstract:

    In large Negative Ion sources of the neutral beam injector (NBI) for large fusIon devices, such as ITER and JT-60SA, one of issues is that Negative Ion beam might be partially intercepted at acceleratIon grids due to a spatial non-uniformity of Negative Ion productIon on large extractIon area. Previous experiments have shown that fast electrons emitted from filament cathodes are transported in a longitudinal directIon by B × grad B drift and the spatial distributIon of electron temperature (Te) is strongly related with the non-uniformity of Negative Ion productIon. In this study, a three-dimensIonal electron transport analysis code including detailed collisIon processes has been developed to clarify a physical mechanism of non-uniform Te distributIon. Electron density and temperature in the analysis agree well with measurements by Langmuir probe in the JAEA 10A Ion source. Then, this study has clarified that the non-uniformity of Te distributIon is mainly caused by the following reasons; i) fast electrons...

  • improvement of voltage holding capability in the 500 kev Negative Ion source for jt 60sa
    Review of Scientific Instruments, 2010
    Co-Authors: Y Tanaka, M. Hanada, M. Taniguchi, K. Watanabe, T Inoue, N. Akino, A Kojima, Tatsuo Shimizu, K Ohshima, M Kashiwagi
    Abstract:

    Voltage holding capability of JT-60 Negative Ion source that has a large electrostatic Negative Ion accelerator with 45 cm×1.1 m acceleratIon grids was experimentally examined and improved to realize 500 keV, 22 A, and 100 s D− Ion beams for JT-60 Super Advanced. The gap lengths in the acceleratIon stages were extended to reduce electric fields in a gap between the large grids and at the corner of the support flanges from the original 4–5 to 3–4 kV/mm. As a result, the voltage holding capability without beam acceleratIon has been successfully improved from 400 to 500 kV. The pulse duratIon to hold 500 kV reached 40 s of the power supply limitatIon.

A Kojima - One of the best experts on this subject based on the ideXlab platform.

  • analysis of the beam halo in Negative Ion sources by using 3d3v pic code
    Review of Scientific Instruments, 2016
    Co-Authors: K Miyamoto, M. Hanada, Akiyoshi Hatayama, A Kojima, S Nishioka, I Goto, J Hiratsuka
    Abstract:

    The physical mechanism of the formatIon of the Negative Ion beam halo and the heat loads of the multi-stage acceleratIon grids are investigated with the 3D PIC (particle in cell) simulatIon. The following physical mechanism of the beam halo formatIon is verified: The beam core and the halo consist of the Negative Ions extracted from the center and the periphery of the meniscus, respectively. This difference of Negative Ion extractIon locatIon results in a geometrical aberratIon. Furthermore, it is shown that the heat loads on the first acceleratIon grid and the second acceleratIon grid are quantitatively improved compared with those for the 2D PIC simulatIon result.

  • 22 a beam productIon of the uniform Negative Ions in the jt 60 Negative Ion source
    Fusion Engineering and Design, 2015
    Co-Authors: Masafumi Yoshida, M Kashiwagi, M. Hanada, Akiyoshi Hatayama, L. R. Grisham, N. Akino, A Kojima, T Shibata, Takashi Yamamoto, Y. Endo
    Abstract:

    Abstract In order to improve the spatial uniformity of the Negative Ion beam and to produce high current Negative Ion beams in a large Negative Ion source, a magnetic field configuratIon is modified from an original transverse filter to a tent-shaped filter, in combinatIon with reducing the magnetic field strength in the JT-60 Negative Ion source. As a result, the beam uniformity is improved from 68% to 83% over an area of the whole extractIon area of 450 × 1100 mm 2 . The improvement of the beam uniformity leads to the productIon of 32 A H − Ion beams with the whole extractIon area. The obtained beam current fulfills the requirement for JT-60SA.

  • progress in long pulse productIon of powerful Negative Ion beams for jt 60sa and iter
    Nuclear Fusion, 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, N. Akino, M. Komata, M Yoshida, N Umeda, K. Mogaki
    Abstract:

    Significant progress in the extensIon of pulse duratIons of powerful Negative Ion beams has been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long-pulse productIon/acceleratIon of Negative Ion beams in JT-60SA and ITER, new technologies have been developed in the JT-60SA Ion source and the MeV accelerator in Japan Atomic Energy Agency.As for the long-pulse productIon of high-current Negative Ions for the JT-60SA Ion source, the pulse duratIons have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA Ion source, which satisfies the required pulse duratIon of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform Negative Ion productIons with the modified tent-shaped filter field configuratIon. Moreover, each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER Ion source because the sustainment of the caesium coverage in the large extractIon area is one of the common issues between JT-60SA and ITER.As for the long-pulse acceleratIon of high power density beams in the MeV accelerator for ITER, the pulse duratIon of MeV-class Negative Ion beams has been extended by more than 2 orders of magnitude by modifying the extractIon grid with a high cooling capability and a high transmissIon of Negative Ions. A long-pulse acceleratIon of 60 s has been achieved at 70 MW m−2 (683 keV, 100 A m−2) which has reached the power density of JT-60SA level of 65 MW m−2. No degradatIons of the voltage holding capability of the acceleratIon voltage and the beam optics due to the distortIon of the acceleratIon grids have been observed in this power density level.These results are the longest pulse duratIons of high-current and high-power-density Negative Ion beams in the world.

  • long pulse productIon of high current Negative Ion beam by using actively temperature controlled plasma grid for jt 60sa Negative Ion source
    FOURTH INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS BEAMS AND SOURCES (NIBS 2014), 2015
    Co-Authors: A Kojima, M Kashiwagi, M. Hanada, K. Watanabe, Hiroyuki Tobari, M Yoshida, N Umeda, J Hiratsuka, L. R. Grisham
    Abstract:

    The temperature control system of the large-size plasma grid has been developed to realize the long pulse productIon of high-current Negative Ions for JT-60SA. By using this prototype system for the JT-60SA Ion source, 15 A Negative Ions has been sustained for 100 s for the first time, which is three times longer than that obtained in JT-60U. In this system, a high-temperature fluorinated fluid with a high boiling point of 270 degree Celsius is circulated in the cooling channels of the plasma grids (PG) where a cesium (Cs) coverage is formed to enhance the Negative Ion productIon. Because the PG temperature control had been applied to only 10% of the extractIon area previously, the prototype PG with the full extractIon area (110 cm × 45 cm) was developed to increase the Negative Ion current in this time. In the preliminary results of long pulse productIons of high-current Negative Ions at a Cs conditIoning phase, the Negative Ion productIon was gradually degraded in the last half of 100 s pulse where the ...

  • achievement of 500 kev Negative Ion beam acceleratIon on jt 60u Negative Ion based neutral beam injector
    Nuclear Fusion, 2011
    Co-Authors: A Kojima, M. Hanada, N. Akino, M. Komata, K. Mogaki, M Kawai, M Kazawa, Y Tanaka, K Usui, S Sasaki
    Abstract:

    Hydrogen Negative Ion beams of 507 keV, 1 A and 486 keV, 2.8 A have been successfully produced in the JT-60U Negative Ion source with a three-stage accelerator by overcoming a poor voltage holding of the accelerator with large-size grids of ~2 m2. This is the first result of H− beam acceleratIon up to 500 keV at a high current of over 1 A. In order to improve the voltage holding capability, the breakdown voltages of the large-size grids and small-size electrodes with uniform and locally strong electric fields were examined by changing the gap length. It was found that the voltage holding of the large-size grids was below half of that of the small-size electrodes with a uniform electric field which was used in the design of the accelerator. This degradatIon was found to be caused by the local electric field concentratIons in additIon to the size. Based on the results of the voltage holding tests and beam optics calculatIons, the gap lengths of the large-size grids were tuned to have a capability to sustain 600 kV. As a result, the gap tuning realized stable voltage holding during beam acceleratIons without significant degradatIons of the beam optics and stripping loss. These results indicated that stable 500 keV beam acceleratIons required for JT-60SA are feasible and this gap tuning is also applicable for the design of ITER accelerator.