The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform

Keishi Sakamoto - One of the best experts on this subject based on the ideXlab platform.

  • A study on multi frequency operation of RF transmission System for EC H&Cd System
    Nuclear Fusion, 2018
    Co-Authors: Yasuhisa Oda, Ryosuke Ikeda, Ken Kajiwara, Koji Takahashi, J.p. Anderson, John L. Doane, Keishi Sakamoto
    Abstract:

    To study the performance of multi frequency operation of transmission lines for electron cyclotron heating and current drive (EC H&Cd) Systems, the performance of a transmission line (TL) with 104 GHz/137 GHz/170 GHz operation was evaluated using a multi frequency gyrotron. The TL test stand for multi frequency high-power operation was composed from corrugated waveguides with 63.5 mm inner diameter and TL components, such as miter bends. The coupling efficiency of gyrotron power into the TL inlet, mode purity at the TL end, and power transmission efficiency were measured for three frequency operations. The transmission efficiency of the 40 m length TL remained at 94%–95% for three frequencies and that of the MOU varied because of the quasi-optical design in the MOU. The mode conversion in TL was found to be less than 2% for three frequencies. These results indicate that the TL using corrugated waveguide can deliver radio frequency power from the gyrotron to the launcher with similar performance expected in single frequency operation in ITER

  • Study of sub-terahertz high power gyrotron for ECH&Cd System of DEMO
    2015 IEEE International Conference on Plasma Sciences (ICOPS), 2015
    Co-Authors: Keishi Sakamoto, Tsuyoshi Kariya, Yasuhisa Oda, Ryutaro Minami, Ryosuke Ikeda, Ken Kajiwara, Takayuki Kobayashi, Koji Takahashi, Shinichi Moriyama, Tsuyoshi Imai
    Abstract:

    For the Electron cyclotron resonance heating and current drive (ECH&Cd) System on fusion DEMO reactor, the high power mm-wave of 200 GHz ∼300 GHz is expected. To increase the gyrotron frequency, extremely high-order oscillation mode should be adopted to suppress the Ohmic loss on the resonator wall less than ∼20 MW/m2. Here, we designed and fabricated a 300 GHz gyrotron of TE 32,18 mode oscillation and started a short pulse experiment to investigate the oscillation characteristics of the high order mode at ∼300 GHz. As a preliminary result, we demonstrated the power generation of ∼0.5 MW at ∼300 GHz oscillation at the oscillation mode of TE 32,18 , and other modes.

  • High power millimeter wave experiment of torus diamond window prototype for ITER EC H&Cd System
    Fusion Engineering and Design, 2013
    Co-Authors: Koji Takahashi, Keishi Sakamoto, Yasuhisa Oda, Ken Kajiwara, T. Omori, M. A. Henderson
    Abstract:

    Abstract The design of the torus diamond window for the ITER electron cyclotron heating and current drive (EC H&Cd) System has advanced considering a reliable and manufacturable structure. The diamond window prototype was fabricated based on the design and the high power experiment was carried out to verify the millimeter wave transmission capability. Transmission of 740 kW-100 s was demonstrated and no significant temperature increase of the window structure and no damage on the diamond disk were obtained. The temperature saturation of the cooling water for the window was observed and loss tangent of 7.8 × 10−6, which was the lowest value that we had ever obtained at JAEA, was evaluated. This result indicates that the diamond window design is feasible and promising the high power more than 1 MW transmission.

  • Development of high voltage power supply for the KSTAR 170 GHz ECH and Cd System
    Fusion Engineering and Design, 2013
    Co-Authors: J.h. Jeong, Y.s. Bae, M. Joung, H. J. Kim, S.i. Park, W. S. Han, Jik-soo Kim, H.l. Yang, Jong-gu Kwak, Keishi Sakamoto
    Abstract:

    Abstract A 3.6 MW (66 kV/55 A) DC power supply System was developed for the 170 GHz EC H&Cd System in KSTAR. The power supply System consists of a cathode power supply (CPS), an anode power supply (APS) and a body power supply (BPS). The cathode power supply is capable of supplying a maximum voltage of −66 kV and a current of 55 A to the cathode with respect to the collector using pulse step modulation (PSM). The high voltage switching System for the cathode is made by a fast MOS-FET solid-state switch which can turn off the high voltage to the cathode within 3 μs in the occurrence of gyrotron faults. The APS is a voltage divider System consisting of a fixed resistor and zener diode units with the capability of 60 kV stand-off voltage. The anode voltage with respect to the cathode is controlled in a range of 0–60 kV by turning the MOS-FET switches connected in parallel to each zener diode on and off. For high frequency current modulation of the gyrotron, the parallel discharge switch is introduced between the cathode and anode in order to clamp the charged voltage in the stray capacitance. The BPS is a DC power supply with the capability of 50 kV/160 mA. The nominal operation parameter of BPS was 23 kV and 10 mA, respectively, and the voltage output is regulated with a stability of 0.025% of the rated voltage. The series MOS-FET solid-state switch is used for on/off modulation in the body voltage sychronizing with anode voltage. The parallel discharge switch is also introduced between the body and collector for high frequency RF modulation. This paper describes the key features of the high voltage power supply System of the KSTAR 170 GHz gyrotron as well as the test results of the power supply.

  • High power-long pulse transmission experiment of torus diamond window for ITER EC H&Cd System
    2011 International Conference on Infrared Millimeter and Terahertz Waves, 2011
    Co-Authors: Koji Takahashi, Ken Kajiwara, Yasuhisa Oda, Keishi Sakamoto
    Abstract:

    A torus diamond window prototype for an ITER electron cyclotron heating and current drive (EC H&Cd) System was fabricated based on the latest design. It was installed in the ITER relevant transmission line and high power-long pulse experiment was carried out. Transmission of 740kW–100sec and was performed. It was observed that the cooling water temperature was stabilized and significant low loss tangent, 5.54 × 10−6 was estimated. The results promise that our torus diamond window is feasible to high power-long pulse transmission.

Yinhua Xia - One of the best experts on this subject based on the ideXlab platform.

  • discontinuous galerkin methods for short pulse type equations via hodograph transformations
    Journal of Computational Physics, 2019
    Co-Authors: Qian Zhang, Yinhua Xia
    Abstract:

    Abstract In the present paper, we consider the discontinuous Galerkin (DG) methods for solving short pulse (SP) type equations. The short pulse equation has been shown to be completely integrable, which admits the loop-soliton, cuspon-soliton solutions as well as smooth-soliton solutions. Through hodograph transformations, these nonclassical solutions can be profiled as the smooth solutions of the coupled dispersionless (Cd) System or the sine-Gordon equation. Therefore, DG methods can be developed for the Cd System or the sine-Gordon equation to simulate the loop-soliton or cuspon-soliton solutions of the SP equation. The conservativeness or dissipation of the Hamiltonian or momentum for the semi-discrete DG schemes can be proved. Also we modify the above DG schemes and obtain an integration DG scheme. Theoretically the a-priori error estimates have been provided for the momentum conserved DG scheme and the integration DG scheme. We also propose the DG scheme and the integration DG scheme for the sine-Gordon equation, in case the SP equation can not be transformed to the Cd System. All these DG schemes can be applied to the generalized or modified SP type equations. Numerical experiments are provided to illustrate the optimal order of accuracy and capability of these DG schemes.

  • discontinuous galerkin methods for short pulse type equations via hodograph transformations
    arXiv: Numerical Analysis, 2019
    Co-Authors: Qian Zhang, Yinhua Xia
    Abstract:

    In the present paper, we consider the discontinuous Galerkin (DG) methods for solving short pulse (SP) type equations. The short pulse equation has been shown to be completely integrable, which admits the loop-soliton, cuspon-soliton solutions as well as smooth-soliton solutions. Through hodograph transformations, these nonclassical solutions can be profiled as the smooth solutions of the coupled dispersionless (Cd) System or the sine-Gordon equation. Thus, DG methods can be developed for the Cd System or the sine-Gordon equation to simulate the loop-soliton or cuspon-soliton solutions of the SP equation. The conservativeness or dissipation of the Hamiltonian or momentum for the semi-discrete DG schemes can be proved. Also we modify the above DG schemes and obtain an integration DG scheme. Theoretically the a-priori error estimates have been provided for the momentum conserved DG scheme and the integration DG scheme. We also propose the DG scheme and the integration DG scheme for the sine-Gordon equation, in case the SP equation can not be transformed to the Cd System. All these DG schemes can be adopted to the generalized or modified SP type equations. Numerical experiments are provided to illustrate the optimal order of accuracy and capability of these DG schemes.

Koji Takahashi - One of the best experts on this subject based on the ideXlab platform.

  • A study on multi frequency operation of RF transmission System for EC H&Cd System
    Nuclear Fusion, 2018
    Co-Authors: Yasuhisa Oda, Ryosuke Ikeda, Ken Kajiwara, Koji Takahashi, J.p. Anderson, John L. Doane, Keishi Sakamoto
    Abstract:

    To study the performance of multi frequency operation of transmission lines for electron cyclotron heating and current drive (EC H&Cd) Systems, the performance of a transmission line (TL) with 104 GHz/137 GHz/170 GHz operation was evaluated using a multi frequency gyrotron. The TL test stand for multi frequency high-power operation was composed from corrugated waveguides with 63.5 mm inner diameter and TL components, such as miter bends. The coupling efficiency of gyrotron power into the TL inlet, mode purity at the TL end, and power transmission efficiency were measured for three frequency operations. The transmission efficiency of the 40 m length TL remained at 94%–95% for three frequencies and that of the MOU varied because of the quasi-optical design in the MOU. The mode conversion in TL was found to be less than 2% for three frequencies. These results indicate that the TL using corrugated waveguide can deliver radio frequency power from the gyrotron to the launcher with similar performance expected in single frequency operation in ITER

  • Study of sub-terahertz high power gyrotron for ECH&Cd System of DEMO
    2015 IEEE International Conference on Plasma Sciences (ICOPS), 2015
    Co-Authors: Keishi Sakamoto, Tsuyoshi Kariya, Yasuhisa Oda, Ryutaro Minami, Ryosuke Ikeda, Ken Kajiwara, Takayuki Kobayashi, Koji Takahashi, Shinichi Moriyama, Tsuyoshi Imai
    Abstract:

    For the Electron cyclotron resonance heating and current drive (ECH&Cd) System on fusion DEMO reactor, the high power mm-wave of 200 GHz ∼300 GHz is expected. To increase the gyrotron frequency, extremely high-order oscillation mode should be adopted to suppress the Ohmic loss on the resonator wall less than ∼20 MW/m2. Here, we designed and fabricated a 300 GHz gyrotron of TE 32,18 mode oscillation and started a short pulse experiment to investigate the oscillation characteristics of the high order mode at ∼300 GHz. As a preliminary result, we demonstrated the power generation of ∼0.5 MW at ∼300 GHz oscillation at the oscillation mode of TE 32,18 , and other modes.

  • High power millimeter wave experiment of torus diamond window prototype for ITER EC H&Cd System
    Fusion Engineering and Design, 2013
    Co-Authors: Koji Takahashi, Keishi Sakamoto, Yasuhisa Oda, Ken Kajiwara, T. Omori, M. A. Henderson
    Abstract:

    Abstract The design of the torus diamond window for the ITER electron cyclotron heating and current drive (EC H&Cd) System has advanced considering a reliable and manufacturable structure. The diamond window prototype was fabricated based on the design and the high power experiment was carried out to verify the millimeter wave transmission capability. Transmission of 740 kW-100 s was demonstrated and no significant temperature increase of the window structure and no damage on the diamond disk were obtained. The temperature saturation of the cooling water for the window was observed and loss tangent of 7.8 × 10−6, which was the lowest value that we had ever obtained at JAEA, was evaluated. This result indicates that the diamond window design is feasible and promising the high power more than 1 MW transmission.

  • High power-long pulse transmission experiment of torus diamond window for ITER EC H&Cd System
    2011 International Conference on Infrared Millimeter and Terahertz Waves, 2011
    Co-Authors: Koji Takahashi, Ken Kajiwara, Yasuhisa Oda, Keishi Sakamoto
    Abstract:

    A torus diamond window prototype for an ITER electron cyclotron heating and current drive (EC H&Cd) System was fabricated based on the latest design. It was installed in the ITER relevant transmission line and high power-long pulse experiment was carried out. Transmission of 740kW–100sec and was performed. It was observed that the cooling water temperature was stabilized and significant low loss tangent, 5.54 × 10−6 was estimated. The results promise that our torus diamond window is feasible to high power-long pulse transmission.

Yasuhisa Oda - One of the best experts on this subject based on the ideXlab platform.

  • A study on multi frequency operation of RF transmission System for EC H&Cd System
    Nuclear Fusion, 2018
    Co-Authors: Yasuhisa Oda, Ryosuke Ikeda, Ken Kajiwara, Koji Takahashi, J.p. Anderson, John L. Doane, Keishi Sakamoto
    Abstract:

    To study the performance of multi frequency operation of transmission lines for electron cyclotron heating and current drive (EC H&Cd) Systems, the performance of a transmission line (TL) with 104 GHz/137 GHz/170 GHz operation was evaluated using a multi frequency gyrotron. The TL test stand for multi frequency high-power operation was composed from corrugated waveguides with 63.5 mm inner diameter and TL components, such as miter bends. The coupling efficiency of gyrotron power into the TL inlet, mode purity at the TL end, and power transmission efficiency were measured for three frequency operations. The transmission efficiency of the 40 m length TL remained at 94%–95% for three frequencies and that of the MOU varied because of the quasi-optical design in the MOU. The mode conversion in TL was found to be less than 2% for three frequencies. These results indicate that the TL using corrugated waveguide can deliver radio frequency power from the gyrotron to the launcher with similar performance expected in single frequency operation in ITER

  • progress and status of the gyrotron development for the jt 60sa ech Cd System
    International Conference on Infrared Millimeter and Terahertz Waves, 2015
    Co-Authors: Takayuki Kobayashi, Yasuhisa Oda, Ryosuke Ikeda, Masayuki Sawahata, M. Terakado, S. Hiranai, K. Wada, J. Hinata, K. Yokokura, Katsumichi Hoshino
    Abstract:

    High-power, long-pulse operations of a gyrotron for JT-60SA (Super-Advanced) have been carried out at 110 GHz (1 MW/100 s) and 138 GHz (1 MW/100 s). These results fully satisfied the requirements of the electron cyclotron heating and current drive (ECH/Cd) System in JT-60SA. It was experimentally shown that the higher power operation at each frequency is expected to be acceptable for this gyrotron from the viewpoint of heat load at the cavity resonator, collector, and stray radiation absorbers. An oscillation of 1 MW for 1 s at 82 GHz has been demonstrated as an additional frequency of the same gyrotron. Experiments toward 1.5 MW or higher at 110 GHz and 138GHz are ongoing.

  • Study of sub-terahertz high power gyrotron for ECH&Cd System of DEMO
    2015 IEEE International Conference on Plasma Sciences (ICOPS), 2015
    Co-Authors: Keishi Sakamoto, Tsuyoshi Kariya, Yasuhisa Oda, Ryutaro Minami, Ryosuke Ikeda, Ken Kajiwara, Takayuki Kobayashi, Koji Takahashi, Shinichi Moriyama, Tsuyoshi Imai
    Abstract:

    For the Electron cyclotron resonance heating and current drive (ECH&Cd) System on fusion DEMO reactor, the high power mm-wave of 200 GHz ∼300 GHz is expected. To increase the gyrotron frequency, extremely high-order oscillation mode should be adopted to suppress the Ohmic loss on the resonator wall less than ∼20 MW/m2. Here, we designed and fabricated a 300 GHz gyrotron of TE 32,18 mode oscillation and started a short pulse experiment to investigate the oscillation characteristics of the high order mode at ∼300 GHz. As a preliminary result, we demonstrated the power generation of ∼0.5 MW at ∼300 GHz oscillation at the oscillation mode of TE 32,18 , and other modes.

  • Progress and status of the gyrotron development for the JT-60SA ECH/Cd System
    2015 40th International Conference on Infrared Millimeter and Terahertz waves (IRMMW-THz), 2015
    Co-Authors: Takayuki Kobayashi, Yasuhisa Oda, Ryosuke Ikeda, Masayuki Sawahata, M. Terakado, S. Hiranai, K. Wada, J. Hinata, K. Yokokura, Katsumichi Hoshino
    Abstract:

    High-power, long-pulse operations of a gyrotron for JT-60SA (Super-Advanced) have been carried out at 110 GHz (1 MW/100 s) and 138 GHz (1 MW/100 s). These results fully satisfied the requirements of the electron cyclotron heating and current drive (ECH/Cd) System in JT-60SA. It was experimentally shown that the higher power operation at each frequency is expected to be acceptable for this gyrotron from the viewpoint of heat load at the cavity resonator, collector, and stray radiation absorbers. An oscillation of 1 MW for 1 s at 82 GHz has been demonstrated as an additional frequency of the same gyrotron. Experiments toward 1.5 MW or higher at 110 GHz and 138GHz are ongoing.

  • High power millimeter wave experiment of torus diamond window prototype for ITER EC H&Cd System
    Fusion Engineering and Design, 2013
    Co-Authors: Koji Takahashi, Keishi Sakamoto, Yasuhisa Oda, Ken Kajiwara, T. Omori, M. A. Henderson
    Abstract:

    Abstract The design of the torus diamond window for the ITER electron cyclotron heating and current drive (EC H&Cd) System has advanced considering a reliable and manufacturable structure. The diamond window prototype was fabricated based on the design and the high power experiment was carried out to verify the millimeter wave transmission capability. Transmission of 740 kW-100 s was demonstrated and no significant temperature increase of the window structure and no damage on the diamond disk were obtained. The temperature saturation of the cooling water for the window was observed and loss tangent of 7.8 × 10−6, which was the lowest value that we had ever obtained at JAEA, was evaluated. This result indicates that the diamond window design is feasible and promising the high power more than 1 MW transmission.

Qian Zhang - One of the best experts on this subject based on the ideXlab platform.

  • discontinuous galerkin methods for short pulse type equations via hodograph transformations
    Journal of Computational Physics, 2019
    Co-Authors: Qian Zhang, Yinhua Xia
    Abstract:

    Abstract In the present paper, we consider the discontinuous Galerkin (DG) methods for solving short pulse (SP) type equations. The short pulse equation has been shown to be completely integrable, which admits the loop-soliton, cuspon-soliton solutions as well as smooth-soliton solutions. Through hodograph transformations, these nonclassical solutions can be profiled as the smooth solutions of the coupled dispersionless (Cd) System or the sine-Gordon equation. Therefore, DG methods can be developed for the Cd System or the sine-Gordon equation to simulate the loop-soliton or cuspon-soliton solutions of the SP equation. The conservativeness or dissipation of the Hamiltonian or momentum for the semi-discrete DG schemes can be proved. Also we modify the above DG schemes and obtain an integration DG scheme. Theoretically the a-priori error estimates have been provided for the momentum conserved DG scheme and the integration DG scheme. We also propose the DG scheme and the integration DG scheme for the sine-Gordon equation, in case the SP equation can not be transformed to the Cd System. All these DG schemes can be applied to the generalized or modified SP type equations. Numerical experiments are provided to illustrate the optimal order of accuracy and capability of these DG schemes.

  • discontinuous galerkin methods for short pulse type equations via hodograph transformations
    arXiv: Numerical Analysis, 2019
    Co-Authors: Qian Zhang, Yinhua Xia
    Abstract:

    In the present paper, we consider the discontinuous Galerkin (DG) methods for solving short pulse (SP) type equations. The short pulse equation has been shown to be completely integrable, which admits the loop-soliton, cuspon-soliton solutions as well as smooth-soliton solutions. Through hodograph transformations, these nonclassical solutions can be profiled as the smooth solutions of the coupled dispersionless (Cd) System or the sine-Gordon equation. Thus, DG methods can be developed for the Cd System or the sine-Gordon equation to simulate the loop-soliton or cuspon-soliton solutions of the SP equation. The conservativeness or dissipation of the Hamiltonian or momentum for the semi-discrete DG schemes can be proved. Also we modify the above DG schemes and obtain an integration DG scheme. Theoretically the a-priori error estimates have been provided for the momentum conserved DG scheme and the integration DG scheme. We also propose the DG scheme and the integration DG scheme for the sine-Gordon equation, in case the SP equation can not be transformed to the Cd System. All these DG schemes can be adopted to the generalized or modified SP type equations. Numerical experiments are provided to illustrate the optimal order of accuracy and capability of these DG schemes.