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Journal Articles

Optimization of millimeter wave system in ITER equatorial EC H&CD launcher

Kajiwara, Ken; Takahashi, Koji; Oda, Yasuhisa; Kobayashi, Noriyuki*; Sakamoto, Keishi

Fusion Engineering and Design, 89(1), p.6 - 10, 2014/01

 Times Cited Count:3 Percentile:24.12(Nuclear Science & Technology)

Journal Articles

A Framework for analysis of abortive colony size distributions using a model of branching processes in irradiated normal human fibroblasts

Sakashita, Tetsuya; Hamada, Nobuyuki*; Kawaguchi, Isao*; Ouchi, Noriyuki; Hara, Takamitsu*; Kobayashi, Yasuhiko; Saito, Kimiaki

PLOS ONE (Internet), 8(7), p.e70291_1 - e70291_10, 2013/07

 Times Cited Count:7 Percentile:33.97(Multidisciplinary Sciences)

Clonogenicity gives important information about the cellular reproductive potential following ionizing irradiation. We firstly plotted the experimentally determined colony size distribution of abortive colonies in irradiated normal human fibroblasts, and found the linear relationship on the log-log plot. By applying the simple model of branching processes to the linear relationship, we found the persistent reproductive cell death (RCD) over several generations following irradiation. To verify the estimated probability of RCD, abortive colony size distribution ($$leq$$15 cells/colony) and the surviving fraction were simulated by the Monte Carlo computational approach. Radiation-induced RCD (i.e. excess probability) lasted over 16 generations and mainly consisted of two components in the early and late phases. We found that short-term RCD is critical to the abortive colony size distribution, and long-lasting RDC is important for the dose response of the surviving fraction.

Journal Articles

Nuclear analysis of ITER equatorial EC launcher

Takahashi, Koji; Iida, Hiromasa*; Kobayashi, Noriyuki*; Kajiwara, Ken; Sakamoto, Keishi; Omori, Toshimichi*; Henderson, M.*

Fusion Science and Technology, 63(1T), p.156 - 159, 2013/05

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Nuclear analysis of the ITER equatorial EC launcher has been carried out to determine heat and/or particle loads on its components and also to evaluate the possibility of "hands-on maintainability" (personnel accessibility) to the launcher back-end. Monte Carlo code "MCNP5" is applied to simulate the radiation leak from fusion plasma to the special region around the launcher. The results indicate a significant radiation leak at the gaps between the port walls and port plug frame and at the waveguide bundles in the launcher. Another significant neutron leakage is through the port wall consisting of only stainless steel but without light isotopes such as water. The shut down dose rates was estimated at the port interspace behind the launcher at the level of the required value of 100 $$mu$$Sv/h. This analysis offers the potential to modify the launchers shielding layout to minimize the above leakage and further reduce the shut down dose rates in the regions of personnel access.

Journal Articles

Development of ITER equatorial EC launcher

Takahashi, Koji; Kajiwara, Ken; Oda, Yasuhisa; Kobayashi, Noriyuki*; Sakamoto, Keishi; Omori, Toshimichi*; Henderson, M.*

Proceedings of 24th IAEA Fusion Energy Conference (FEC 2012) (CD-ROM), 8 Pages, 2013/03

The ITER equatorial EC launcher is making a large technology to injecting $$geq$$20 M and CW operation. The design of the shield blanket structure that tolerates thermal and electromagnetic load is attained. The port plug structure considering the fabrication process applying HIP and TIG-welding are designed. The mm-wave design that enables to guide the wave power of $$geq$$20 MW into plasma with toroidal steering capability of 20$$^{circ}$$ $$sim$$ 40$$^{circ}$$ and efficiency of 98.4 $$sim$$ 99% assuming HE11 fundamental wave mode + TEM000 gaussian mode are proceeded. Reduction of the heat load to 2.1 MW/m$$^{2}$$ on the steering mirror are attained. These results allow the transmission of 2.0 MW per a waveguide and the required radiation profile from the launcher. The full scale mock-up of the mm-wave launching system consisting of the waveguides and the mirrors and the subcomponents such as the steering mechanism of the mirror, the cooling water lines and etc., are fabricated to investigate the design availability. High power (0.5 MW) experiment of the mock-up confirmed the expected wave beam propagation and steering capability of 20$$^{circ}$$ $$sim$$ 40$$^{circ}$$. The mock-up of the shield blanket module and the partial mock-up of the port plug structure are fabricated based on the present design to investigate the manufacturability and the performance of the cooling water flow. The results will reflect back to the fabrication design of the structural components of the equatorial launcher.

Journal Articles

High power millimeter wave experiment of ITER relevant electron cyclotron heating and current drive system

Takahashi, Koji; Kajiwara, Ken; Oda, Yasuhisa; Kasugai, Atsushi; Kobayashi, Noriyuki*; Sakamoto, Keishi; Doane, J.*; Olstad, R.*; Henderson, M.*

Review of Scientific Instruments, 82(6), p.063506_1 - 063506_7, 2011/06

 Times Cited Count:19 Percentile:64.3(Instruments & Instrumentation)

High power, long pulse millimeter (mm) wave experiments of the RF test stand (RFTS) of JAEA were performed. The system consists of a 1 MW/170 GHz gyrotron, a long and short distance transmission line (TL) and an equatorial launcher (EL) mock-up. The RFTS has an ITER-relevant configuration, i.e., that is consisted by a 1 MW-170 GHz gyrotron, mm wave TL and EL mock-up. The TL is composed of a matching optics unit, evacuated circular corrugated waveguides, 6 miter bends, an in-line waveguide switch, an isolation valve. The Gaussian-like beam radiation with the steering capability of 20-40$$^{circ}$$ from the EL mock-up was also successfully proved. The high power long pulse power transmission test was conducted with the metallic load replaced by the EL mock-up, and the transmission of 1 MW/800 s and 0.5 MW/1000 sec were successfully demonstrated with no arcing and no damages. The transmission efficiency of the TL was 96%. The results prove the feasibility of the ITER electron cyclotron heating and current drive system.

Journal Articles

Progress of high power 170 GHz gyrotron in JAEA

Sakamoto, Keishi; Kasugai, Atsushi; Kajiwara, Ken; Takahashi, Koji; Oda, Yasuhisa; Hayashi, Kazuo; Kobayashi, Noriyuki*

Nuclear Fusion, 49(9), p.095019_1 - 095019_6, 2009/09

Recent progress on the high power gyrotron development in JAEA is presented. The gyrotron is featured to have a triode type magnetron injection gun, a cylindrical resonator working at 170 GHz with TE$$_{31,8}$$ mode, a water-cooled diamond window and a depressed collector. After the demonstration of ITER basic performance, the gyrotron has been operated for 3 years, and recorded $$sim$$ 200 GJ of total output energy. In the next, a gyrotron which oscillates at higher order resonator mode, TE$$_{31,12}$$, is designed and fabricated to study the long pulse oscillation at greater than 1 MW. In parallel, feasibility studies of a CW-power modulation for NTM (Neo classical Tearing Mode) stabilization, a dual frequency gyrotron and a rapid frequency control are carried out. It is shown that these gyrotrons will be available with present technologies.

Journal Articles

Progress of high power 170 GHz gyrotron in JAEA

Sakamoto, Keishi; Kasugai, Atsushi; Kajiwara, Ken; Takahashi, Koji; Oda, Yasuhisa; Hayashi, Kazuo; Kobayashi, Noriyuki*

Nuclear Fusion, 49(9), p.095019_1 - 095019_6, 2009/09

 Times Cited Count:73 Percentile:92.81(Physics, Fluids & Plasmas)

Journal Articles

Progress on the heating and current drive systems for ITER

Jacquinot, J.*; Albajar, F.*; Beaumont, B.*; Becoulet, A.*; Bonicelli, T.*; Bora, D.*; Campbell, D.*; Chakraborty, A.*; Darbos, C.*; Decamps, H.*; et al.

Fusion Engineering and Design, 84(2-6), p.125 - 130, 2009/06

 Times Cited Count:24 Percentile:82.52(Nuclear Science & Technology)

The electron cyclotron (EC), ion cyclotron (IC), neutral beam (NB) and, lower hybrid (LH) systems for ITER have been reviewed in 2007/2008 in light of progress of physics and technology. Although the overall specifications are unchanged, notable changes have been approved. Firstly, the full 73MW should be commissioned and available on a routine basis before the D/T phase. Secondly, the possibility to operate the NB at full power during the hydrogen phase requiring new shine through protection; IC with 2 antennas with increased robustness; 2 MW transmission systems to provide an easier upgrading of the EC power; the addition of a building dedicated to the RF power sources and to a testing facility for acceptance of diagnostics and heating port plugs. Thirdly, the need of a plan for developing, in time for the active phase, a CD system such as LH suitable for very long pulse operation of ITER was recognized.

Journal Articles

Long pulse and high power repetitive operation of the 170 GHz ITER gyrotron

Kajiwara, Ken; Kasugai, Atsushi; Oda, Yasuhisa; Takahashi, Koji; Kobayashi, Noriyuki*; Sakamoto, Keishi

Plasma and Fusion Research (Internet), 4, p.006_1 - 006_3, 2009/03

Journal Articles

Design of a high power millimeter wave launcher for EC H&CD system on ITER

Kajiwara, Ken; Takahashi, Koji; Kobayashi, Noriyuki; Kasugai, Atsushi; Sakamoto, Keishi

Fusion Engineering and Design, 84(1), p.72 - 77, 2009/01

 Times Cited Count:14 Percentile:67.16(Nuclear Science & Technology)

Journal Articles

Improved design of an ITER equatorial EC launcher

Takahashi, Koji; Kajiwara, Ken; Kobayashi, Noriyuki; Kasugai, Atsushi; Sakamoto, Keishi

Nuclear Fusion, 48(5), p.054014_1 - 054014_9, 2008/05

 Times Cited Count:24 Percentile:66.76(Physics, Fluids & Plasmas)

The development of an ITER equatorial EC launcher for the improved design has being proceeded. The sustainable design of the front shield modules against electromagnetic forces was analytically obtained. The steering mirror mock-up including the spiral cooling tubes was fabricated based on the present design with application of hot isostatic pressing technique to bond the copper alloy mirror body and the embedded stainless steel cooling tubes. The test of water flow was carried out and the expected flow rate was successfully obtained. A quasi-optical transmission layout has been proposed instead of the waveguide lines. It is verified that transmission loss at the QO region is 1.1$$sim$$2.2%, which is comparable to the reference design. The peak heat load on the steering mirror surface could be reduced by 55%, which makes the mirror design relaxed.

Journal Articles

Steady-state operation of 170 GHz-1 MW gyrotron for ITER

Kasugai, Atsushi; Sakamoto, Keishi; Takahashi, Koji; Kajiwara, Ken; Kobayashi, Noriyuki

Nuclear Fusion, 48(5), p.054009_1 - 054009_6, 2008/05

 Times Cited Count:72 Percentile:93.3(Physics, Fluids & Plasmas)

Journal Articles

Design of electron cyclotron heating and current drive system of ITER

Kobayashi, Noriyuki; Bigelow, T.*; Bonicelli, T.*; Cirant, S.*; Denisov, G.*; Heidinger, R.*; Henderson, M.*; Hogge, J.-P.*; Piosczyk, B.*; Ramponi, G.*; et al.

AIP Conference Proceedings 933, p.413 - 416, 2007/10

Since the EDA 2001, Design of Electron Cyclotron Heating and Current Drive (ECH&CD) System have been modified due to progress of physics understanding and change of interface. Nominal RF power 20 MW is injected by four upper launchers or one equatorial launcher. RF beams are steered by a front steering mirror. DCHV power supply will be composed of IGBT pulse step modulators because of high frequency modulation and design flexibility to three different types of 170 GHz gyrotrons from three parties. The RF power is transmitted by 63.5 mm dia corrugated waveguide and switched by a waveguide switch between the upper launcher and the equatorial launcher. A start-up system for initial discharge is composed of three 127.5 GHz gyrotrons and dedicated DCHV power supply. Three of transmission lines are shared between 170 GHz and 127.5 GHz gyrotrons to inject start-up RF beam through the equatorial launcher. R&Ds for high power long pulse have been on-going to obtain a reliable ITER ECH&CD system.

Journal Articles

Progress on design and development of ITER equatorial launcher; Analytical investigation and R&D of the launcher components for the design improvement

Takahashi, Koji; Kobayashi, Noriyuki; Omori, Junji; Suzuki, Satoshi; Kasugai, Atsushi; Sakamoto, Keishi

Fusion Science and Technology, 52(2), p.266 - 280, 2007/08

 Times Cited Count:25 Percentile:83.44(Nuclear Science & Technology)

Progress on design of an ITER equatorial EC Launcher with analytical and R&D studies of the components is described. The modified design of the front shield module is proposed with electromagnetic and structure analysis. The analytical investigation of the modified steering mirror design shows that maximum temperature and stress intensity are 289$$^{circ}$$C and 336 MPa on the mirror surface (copper alloy) and the inner surface of cooling tube (SS316) in the mirror, respectively. These results are less than allowable level. High heat irradiation experiment of the mirror mock-up and fatigue test of the spiral tube were carried out and their results convinced that the concept of the steering mirror structure was feasible. The results on neutron irradiation test of the composing material and the alternatives such as polyimide and liquid crystal polymer for an ultrasonic motor indicate that the motor with those materials is available for the ITER launcher.

Journal Articles

Achievement of robust high-efficiency 1 MW oscillation in the hard-self-excitation region by a 170 GHz continuous-wave gyrotron

Sakamoto, Keishi; Kasugai, Atsushi; Takahashi, Koji; Minami, Ryutaro*; Kobayashi, Noriyuki; Kajiwara, Ken

Nature Physics, 3(6), p.411 - 414, 2007/06

 Times Cited Count:192 Percentile:97.33(Physics, Multidisciplinary)

The first 1 MW quasi-continuous wave generation is demonstrated at 170 GHz gyrotron of TE31,8 resonator mode with outstanding efficiency of greater than 55 percent. The robust high efficiency oscillation is obtained in a hard self-excitation region with an active control of gyrotron parameters. Furthermore, a novel nonlinear process is found that the desired TE31,8 mode is excited as a parasitic mode of an adjacent TE30,8 mode and finally the TE31,8 dominates a system. This effect extends a substantial soft self-excitation region of the desired mode significantly.

Journal Articles

Investigation of transmission characteristic in corrugated waveguide transmission lines for fusion application

Takahashi, Koji; Kajiwara, Ken; Kasugai, Atsushi; Kobayashi, Noriyuki; Sakamoto, Keishi

Proceedings of 8th IEEE International Vacuum Electronics Conference (IVEC 2007), p.275 - 276, 2007/05

The 170GHz, high power and long pulse (0.46MW/4min) experiment of the ITER relevant transmission line that consited of corrugated waveguides and 7 miterbends was demonstrated. The transmission efficiency was 92%, which was almost equivalent value to the ITER requirement. No clear peak of temperature increase corresponding to the beat wavelength of this waveguide between HE11 and HE12 and between HE11 and HE13 was observed. The significant temperature near and between the bends was, however, obtained. These results indicate that the content of HE12 and HE13 mode is extremely low and the bends generate the unexpected higher order modes. They are also reflected back to the propagating direction.

Journal Articles

Present status of gyrotron development for ITER and prospect of advanced gyrotron for fusion reactor

Kasugai, Atsushi; Takahashi, Koji; Kajiwara, Ken; Kobayashi, Noriyuki; Sakamoto, Keishi

Heisei-19-Nen Denki Gakkai Zenkoku Taikai Koen Rombunshu, 7, p.7_S9(20) - 7_S9(23), 2007/03

In Japan Atomic Energy Agency, the development of the 170 GHz gyrotron with the oscillation mode of TE31,8 for ITER have been carried out aiming at the achievement of the high power, the long pulse and the high efficiency operation. It was cleared that the enhancement of the gyrotron power and the extension of the pulse length were restricted by unusual oscillation due to a beam current decrease and local heating due to stray radiation loss inside the gyrotron. To solve these problems, the improvement of a radiator and an output circuit on the internal mirror were modified. Furthermore, the beam current was controlled by pre-programming of the cathode heater voltage. And, the oscillation efficiency was enhanced by improvement of the electron beam quality. As the result of these improvements, the steady state operation of 1 hour (3600 s) with the output power of 0.6 MW, which significantly exceeded the typical operation time 400 s of ITER was demonstrated. The operation of a 0.6 MW/1 hour could be obtained by the usual operation method which fixed the cavity magnetic field and the pitch factor of the electron beam. However, it was possible that the state of oscillation is controlled by changing these operation parameters during the shot in the long pulse operation. By the advanced operation mode, the gyrotron output power increased to 0.82 MW with the same beam power (the beam current and the beam voltage) of the 0.6 MW/1 hour operation. The oscillation characteristics in the long pulse operation was clarified, and the advanced operation mode of the gyrotron to the high efficiency oscillation was newly established by controlling a pitch factor of the electron beam and the cavity magnetic field in the long pulse operation. As a result, the high efficiency operation of 56 % with the output power of 0.82 MW was succeeded beyond 600 s (10 min).

Journal Articles

Development of the 170GHz gyrotron and equatorial launcher for ITER

Sakamoto, Keishi; Kasugai, Atsushi; Takahashi, Koji; Minami, Ryutaro*; Kariya, Tsuyoshi*; Mitsunaka, Yoshika*; Kobayashi, Noriyuki

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

no abstracts in English

Journal Articles

High power and high efficiency operation of 170GHz gyrotron

Kasugai, Atsushi; Minami, Ryutaro*; Takahashi, Koji; Kobayashi, Noriyuki; Kariya, Tsuyoshi*; Mitsunaka, Yoshika*; Sakamoto, Keishi

Fusion Science and Technology, 51(2T), p.213 - 216, 2007/02

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Long pulse operation of 170 GHz ITER gyrotron by beam current control

Kasugai, Atsushi; Minami, Ryutaro; Takahashi, Koji; Kobayashi, Noriyuki; Sakamoto, Keishi

Fusion Engineering and Design, 81(23-24), p.2791 - 2796, 2006/11

 Times Cited Count:9 Percentile:53.6(Nuclear Science & Technology)

In JAEA (Japan Atomic Energy Agency, formerly JAERI), development of 170 GHz, 1 MW, CW gyrotron for ITER has been carried out. Key technologies for ITER gyrotron such as a diamond window, a depressed collector for high efficiency operation and a stable operation at 170 GHz/1 MW with higher mode TE31,8 have been developed. By integration of these key technologies, gyrotron performance of 0.5 MW/ 100 sec and 0.9 MW/ 9.2 sec were demonstrated. Hence, next target is a demonstration of long pulse operation. One of the issues which prevent the pulse extension is large beam current decrease due to so called the emission cooling of a cathode. During the operation, the oscillation mode shift from TE31,8 to TE30,8 was caused by the current decrease. Then, the magnetic field of the cavity should be increased to avoid the downshift of the oscillation mode, however, the efficiency decreases and the parasitic oscillation appears in a quasi-optical mode converter. To suppress the beam current decrease and to demonstrate the long pulse operation of the high power gyrotron, pre-programming control of the cathode heater power was applied and the long pulse experiment was carried out to sustain the beam current. As a result, stable electron beam of 1000 s, which is required for ITER operation, was demonstrated without oscillation, and pre-programming control directed the effectiveness for constant beam current. Moreover, in the experiment of the long pulse oscillation with oscillation, the pre-programming control suppressed the beam current decrease. Up to now, stable long pulse operation of $$sim$$8 minutes with 0.2 MW output power was obtained. The output energy of the oscillation is maximum value in the 170GHz ITER gyrotron. Since overheating due to stray radiation inside the gyrotron limit the pulse extension, long pulse operation with high power output will be achieved by enhancement of the cooling and reduction of stray radiation due to modification of a built-in mode converter.

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