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Journal Articles

Comparison between simulations using the PHITS code and activated material analysis

Sukegawa, Atsuhiko; Okuno, Koichi*

IEEE Transactions on Plasma Science, 43(11), p.3916 - 3920, 2015/11

 Times Cited Count:1 Percentile:5.81(Physics, Fluids & Plasmas)

In the present study a comparison between simulations using the PHITS code and activated material analysis of JT-60U has been performed. Neutron transport have been simulated using the Monte Carlo methods PHITS to determine the neutron fluency at the irradiation position. The Activated analysis has been complemented by the foil-activation technique. The preliminary result of these PHITS simulations has been confirmed by comparing the reaction rates of gold, cobalt, and nickel foils activation. The simulation results by PHITS consisted with the measured reaction rate of each foils near the device.

Journal Articles

Design of the precompression mechanism and gravity support for the central solenoid assembly in the JT-60SA tokamak

Tsuchiya, Katsuhiko; Kizu, Kaname; Murakami, Haruyuki; Yoshizawa, Norio; Koide, Yoshihiko; Yoshida, Kiyoshi

IEEE Transactions on Plasma Science, 42(4), p.1042 - 1046, 2014/04

 Times Cited Count:8 Percentile:44.28(Physics, Fluids & Plasmas)

JT-60SA is full superconducting tokamak that was constructed in JAEA Naka site in corporation with JAEA and F4E. The central solenoid (CS) assembly in JT-60SA consists of 4 modules of superconducting solenoid which has outer diameter of $$sim$$2m and height of 1.6m. The currents for each module were independently controlled. CS was designed to produce enough flux to control the plasmas with 5.5 MA during 100 sec. Superconducting conductor for CS consists of Nb$$_{3}$$Sn strands. The support structure for CS assembly consists of the tie-plates (inner and outer), buffer zones and key-blocks. CS must be cooled down to 4K before charging, and modules will be shrunk during this process. The support structure made of stainless steel was also shrunk at 4K. Thermal expansion ratio of stainless steel, however, is different from that of modules, which would result in the gap between modules and supports. In order to cancel this gap, pre-compress mechanism needs to be introduced in the support structure for CS assembly. Mechanical pressure for the pre-compress will be controlled by hydraulic rams that are set at the top of each support. During the pre-compress process in which both key-blocks clamp the modules, tension works at the tie plates. The support structure for CS assembly, especially tie plates, should have sufficient mechanical strength to withstand the stress induced by the pre-compress at room temperature, not only to withstand the electro-magnetic force which was produced during the plasma operation. Space for installation of CS assembly is limited by TF coils, so that cross section of tie-plate is also limited. Final structure was successfully designed to adopt the stainless steel with 0.12$$sim$$0.17 wt% of nitrogen content (SS316LN) for the material of the main parts of support structure.

Journal Articles

Final design of the quench protection circuits for the JT-60SA superconducting magnets

Gaio, E.*; Maistrello, A.*; Coffetti, A.*; Gargano, T.*; Perna, M.*; Novello, L.*; Coletti, A.*; Matsukawa, Makoto; Yamauchi, Kunihito

IEEE Transactions on Plasma Science, 40(3), p.557 - 563, 2012/03

 Times Cited Count:27 Percentile:79.85(Physics, Fluids & Plasmas)

Journal Articles

1 MV vacuum insulation for the ITER neutral beam injectors

Tanaka, Masanobu*; Hemsworth, R. S.*; Kuriyama, Masaaki*; Svensson, L.*; Boilson, D.*; Inoue, Takashi; Tobari, Hiroyuki; Kashiwagi, Mieko; Taniguchi, Masaki; Umeda, Naotaka; et al.

IEEE Transactions on Plasma Science, 39(6), p.1379 - 1385, 2011/06

 Times Cited Count:6 Percentile:30.45(Physics, Fluids & Plasmas)

In the ITER neutral beam injector (NBI) for plasma heating and current drive, 40 A D$${-}$$ ions are accelerated to 1 MeV with a five-stage electrostatic accelerator. Since the accelerator is immersed in vacuum, vacuum insulation of -1 MV is one of critical issues. In order to sustain high voltage of -1 MV, minimum gap length between the accelerator and the vacuum vessel at ground potential was designed to be more than 900 mm on the basis of previous experimental data. High voltage bushing (HVB) acting as an insulating feed-through supplying electric power and cooling water to the accelerator consists of five stack insulator and each stage is designed to withstand -200 kV. A full-scale and single-stage mockup bushing was manufactured and tested to demonstrate stable voltage holding. As a result, DC -203 kV was sustained stably for 5 hours and the insulation design of HVB has been confirmed.

Journal Articles

Numerical matching scheme for stability analysis of flowing plasmas

Shiraishi, Junya; Tokuda, Shinji*

IEEE Transactions on Plasma Science, 38(9), p.2169 - 2176, 2010/09

 Times Cited Count:1 Percentile:4.43(Physics, Fluids & Plasmas)

Numerical implementation and a numerical property of a new matching scheme for stability analysis of flowing plasmas are presented. In the new scheme, the singularities are contained in the inner layer, and the Newcomb equation in the outer regions becomes regular, hence the new scheme is numerically tractable. Also, since the new scheme is based on the boundary layer theory, it can save much computation time.

Journal Articles

Global nonlinear electromagnetic simulations of tokamak turbulence

Bottino, A.*; Scott, B. D.*; Brunner, S.*; McMillan, B. F.*; Tran, T. M.*; Vernay, T.*; Villard, L.*; Jolliet, S.; Hatzky, R.*; Peeters, A. G.*

IEEE Transactions on Plasma Science, 38(9), p.2129 - 2135, 2010/09

 Times Cited Count:24 Percentile:71.36(Physics, Fluids & Plasmas)

Journal Articles

Energy spectra of bremsstrahlung X-rays emitted from an FRP insulator

Tanaka, Yutaka; Ikeda, Yoshitaka; Hanada, Masaya; Kobayashi, Kaoru; Kamada, Masaki; Kisaki, Masashi; Akino, Noboru; Yamano, Yasushi*; Kobayashi, Shinichi*; Grisham, L. R.*

IEEE Transactions on Plasma Science, 37(8), p.1495 - 1498, 2009/08

 Times Cited Count:1 Percentile:4.64(Physics, Fluids & Plasmas)

Voltage holding capability of the JT-60 negative ion source is limited by surface flashover on the FRP insulator. To improve the voltage holding capability of the ion source, the understanding of the surface flashover is required. In this study, electron energy is estimated by measuring the bremsstrahlung X-ray emitted from an FRP insulator. Energy spectra of X-ray were measured for 3 different positions and compared with those of the vacuum gap between electrodes. Near the anode, X-ray spectrum was dominated by the monoenergetic electron. Near the cathode, spectrum peak shifted to low energy compared with that near the anode. This result showed that a large amount of low energy electrons was generated on the surface of the FRP insulator near the cathode.

Journal Articles

Improvement of the quality and stability of electron bunch using countercrossing laser beam

Kotaki, Hideyuki; Daito, Izuru; Kando, Masaki; Hayashi, Yukio; Ma, J.-L.; Chen, L.-M.; Esirkepov, T. Z.; Fukuda, Yuji; Homma, Takayuki; Pirozhkov, A. S.; et al.

IEEE Transactions on Plasma Science, 36(4), p.1760 - 1764, 2008/08

 Times Cited Count:8 Percentile:34.65(Physics, Fluids & Plasmas)

The counter-crossing injection, which is a realistic setup for applications, by two sub-relativistic laser pulses colliding is demonstrated in sub-relativistic intensity laser pulse interaction with plasma. The laser pulses in plasma are self-focused to higher intensity when the laser power is above the threshold of a relativistic self-focusing. The collision of self-focused laser pulses generates a high-quality electron beam with high repeatability. The generated monoenergetic electron beam has 14 MeV of the peak energy, 11% of the energy spread, 22 pC of the charge, 1.6$$pi$$mm mrad of the normalized emittance, and 50% of the repeatability.

Journal Articles

Simultaneous generation of UV harmonics and protons from a thin-foil target with a high-intensity laser

Sagisaka, Akito; Daido, Hiroyuki; Pirozhkov, A. S.; Ma, J.-L.; Yogo, Akifumi; Ogura, Koichi; Orimo, Satoshi; Mori, Michiaki; Nishiuchi, Mamiko; Kawachi, Tetsuya; et al.

IEEE Transactions on Plasma Science, 36(4), p.1812 - 1816, 2008/08

 Times Cited Count:4 Percentile:18.43(Physics, Fluids & Plasmas)

We observe UV harmonics and protons with a thin-foil target irradiated with a high-intensity Ti:sapphire laser. The laser intensity dependency of UV harmonics and proton signal is measured by varying the distance between the target surface and the best focus of the laser beam. In the case of appropriate condition for proton generation with a maximum energy of $$sim$$2.7 MeV, the weak broad spectrum in the UV region is generated. The UV harmonics up to fourth-order are generated as the target is moved away from the best focus position. In this condition the maximum energy of protons is reduced to $$sim$$1 MeV.

Journal Articles

Recent R&D activities of negative-ion-based ion source for JT-60SA

Ikeda, Yoshitaka; Hanada, Masaya; Kamada, Masaki; Kobayashi, Kaoru; Umeda, Naotaka; Akino, Noboru; Ebisawa, Noboru; Inoue, Takashi; Honda, Atsushi; Kawai, Mikito; et al.

IEEE Transactions on Plasma Science, 36(4), p.1519 - 1529, 2008/08

 Times Cited Count:8 Percentile:34.65(Physics, Fluids & Plasmas)

The JT-60SA N-NBI system is required to inject 10 MW for 100 s at 500 keV. Three key issues should be solved for the JT-60SA N-NBI ion source. One is to improve the voltage holding capability. Recent R&D tests suggested that the accelerator with a large area of grids may need a high margin in the design of electric field and a long time for conditioning. The second issue is to reduce the grid power loading. It was found that some beamlets were strongly deflected due to beamlet-beamlet interaction and strike on the grounded grid. The grids are to be designed by taking account of beamlet-beamlet interaction in three-dimensional simulation. Third is to maintain the D- production for 100 s. A simple cooling structure is proposed for the active cooled plasma grid, where a key is the temperature gradient on the plasma grid for uniform D- production. The modified N-NBI ion source will start on JT-60SA in 2015.

Journal Articles

Power loading of electrons ejected from the JT-60 negative ion source

Hanada, Masaya; Ikeda, Yoshitaka; Kamada, Masaki; Grisham, L. R.*

IEEE Transactions on Plasma Science, 36(4), p.1530 - 1535, 2008/08

 Times Cited Count:2 Percentile:9.77(Physics, Fluids & Plasmas)

Power loading of the electrons ejected from the negative ion accelerator to the beam-line was first measured in the negative-ion-based neutral beam injector on JT-60U. At 0.3 Pa of the operating pressure in the arc chamber, the heat flux and the total power load for the single segment were about 8 W/cm$$^{2}$$ and 27 kW for the D$$^{-}$$ ion beam of 300 keV, 3.4 A, respectively. The normalized total power loading on the electron dump was no more than 2.6% of the electric power in the acceleration power supply. About 70% of the total power is originated by the electrons stripped from D$$^{-}$$ ions due to the collisions with residual gas molecules in the accelerator. The calculation of the stripped electron trajectories shows that the electrons stripped in the second acceleration gap are the main origin of the power loading in the beam-line.

Journal Articles

New method to measure the rise time of a fast pulse slicer for laser ion acceleration research

Mori, Michiaki; Yogo, Akifumi; Kiriyama, Hiromitsu; Nishiuchi, Mamiko; Ogura, Koichi; Orimo, Satoshi; Ma, J.*; Sagisaka, Akito; Kanazawa, Shuhei; Kondo, Shuji; et al.

IEEE Transactions on Plasma Science, 36(4), p.1872 - 1877, 2008/08

 Times Cited Count:7 Percentile:30.94(Physics, Fluids & Plasmas)

A dependence of cut-off proton kinetic energy on laser prepulse duration has been observed. ASE pedestal duration is controlled by a fast electro-optic pulse slicer where the risetime is estimated to be 130 ps. We demonstrate a new correlated spectral technique for determining this risetime using a stretched, frequency chirped pulse.

Journal Articles

Heavy-ion microbeams; Development and applications in biological studies

Funayama, Tomoo; Hamada, Nobuyuki*; Sakashita, Tetsuya; Kobayashi, Yasuhiko

IEEE Transactions on Plasma Science, 36(4), p.1432 - 1440, 2008/08

 Times Cited Count:14 Percentile:12.7(Physics, Fluids & Plasmas)

High-LET heavy charged particle radiation has been used in radiotherapy and radiation breeding because of its greater biological effectiveness compared with low-LET radiation. The health risk assessment for astronauts due to space radiation during interplanetary manned missions is also an important issue concerning the biological effects of heavy-ion radiation. Localized irradiation of specific regions within organisms using heavy-ion microbeam systems provides an attractive means of investigating the mechanism of heavy ion radiation action. Additionally, heavy-ion microbeams can be used as a radio-microsurgical tool for analyzing a broad range of biological phenomena. This paper reviews briefly the current status concerning the development of heavy-ion microbeams for use on living organisms with particular emphasis on its applications in biological studies in eukaryotes including plants, silkworm, nematode, and cultured plant and mammalian cells.

Journal Articles

Positive and negative ion sources for magnetic fusion

Hemsworth, R. S.*; Inoue, Takashi

IEEE Transactions on Plasma Science, 33(6), p.1799 - 1813, 2005/12

 Times Cited Count:79 Percentile:92.06(Physics, Fluids & Plasmas)

The positive or negative ion sources which form the primary components of neutral beam injection systems used in magnetic fusion have to meet simultaneously several demanding requirements. This paper describes the underlying physics of modern positive ion sources, which provide the required high proton fraction ($$>$$90%) and high current density ($$approx$$2 kA/m$$^{2}$$) at a low source pressure (0.4 Pa) with a high electrical efficiency and uniformity across the accelerator grids. The development of negative ion sources, which are required if high energy neutral beams are to be produced, is explained. The paper reports that negative ion sources have achieved many of the parameters required of sources for the neutral beam injectors of future fusion devices and reactors, $$>$$200 A/m$$^{2}$$ of D$$^{-}$$ at low pressure, $$<$$0.3 Pa, with low co-extracted electron content. The development needed to meet all the requiremens of future systems is briefly discussed.

Journal Articles

Fusion research by magnetic confinement devices in Japan

Matsuda, Shinzaburo

IEEE Transactions on Plasma Science, 32(2), p.749 - 756, 2004/04

 Times Cited Count:0 Percentile:0.02(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Recent results and modification program of JT-60 toward high integrated performance

Matsukawa, Makoto; JT-60 Team

IEEE Transactions on Plasma Science, 32(1), p.135 - 143, 2004/02

 Times Cited Count:1 Percentile:3.1(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

The Design of a tapered dimple-type mode converter/launcher for high-power gyrotrons

Hirata, Yosuke*; Mitsunaka, Yoshika*; Hayashi, Kenichi*; Ito, Yasuyuki*; Sakamoto, Keishi; Imai, Tsuyoshi

IEEE Transactions on Plasma Science, 31(1), p.142 - 145, 2003/02

 Times Cited Count:11 Percentile:36.11(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

High-voltage test of feedthroughs for a high-power ICRF antenna

Fujii, Tsuneyuki; Moriyama, Shinichi

IEEE Transactions on Plasma Science, 29(2), p.318 - 325, 2001/04

 Times Cited Count:3 Percentile:11.53(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Experimental verification of laser photocathode RF gun as an injector for a laser plasma accelerator

Uesaka, Mitsuru*; Kinoshita, Kenichi*; Watanabe, Takahiro*; Sugahara, Jun*; Ueda, Toru*; Yoshii, Koji*; Kobayashi, Tetsuya*; Halz, N.*; Nakajima, Kazuhisa; Sakai, Fumio*; et al.

IEEE Transactions on Plasma Science, 28(4), p.1133 - 1142, 2000/08

 Times Cited Count:14 Percentile:43.45(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Reconstruction of plasma current profile of tokamaks using combinatorial optimization techniques

Kishimoto, Maki; ; Ara, Katsuyuki; Fujita, Takaaki; *

IEEE Transactions on Plasma Science, 24(2), p.528 - 538, 1996/04

 Times Cited Count:1 Percentile:4.59(Physics, Fluids & Plasmas)

no abstracts in English

23 (Records 1-20 displayed on this page)