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Journal Articles

An Estimation method for an unknown covariance in cross-section adjustment based on unbiased and consistent estimator

Maruyama, Shuhei; Endo, Tomohiro*; Yamamoto, Akio*

Journal of Nuclear Science and Technology, 60(11), p.1372 - 1385, 2023/11

 Times Cited Count:1 Percentile:63.33(Nuclear Science & Technology)

Journal Articles

Comparative study on prediction accuracy improvement methods with the use of integral experiments for neutronic characteristics of fast reactors

Yokoyama, Kenji; Kitada, Takanori*

Proceedings of 2018 International Congress on Advances in Nuclear Power Plants (ICAPP 2018) (CD-ROM), p.1221 - 1230, 2018/04

no abstracts in English

Journal Articles

Dimension-reduced cross-section adjustment method based on minimum variance unbiased estimation

Yokoyama, Kenji; Yamamoto, Akio*; Kitada, Takanori*

Journal of Nuclear Science and Technology, 55(3), p.319 - 334, 2018/03

 Times Cited Count:8 Percentile:61.87(Nuclear Science & Technology)

A new formulation of the cross-section adjustment methodology with the dimensionality reduction technique has been derived. This new formulation is proposed as the dimension reduced cross-section adjustment method (DRCA). Since the derivation of DRCA is based on the minimum variance unbiased estimation (MVUE), an assumption of normal distribution is not required. The result of DRCA depends on a user-defined matrix that determines the dimension reduced feature subspace. We have examine three variations of DRCA, namely DRCA1, DRCA2, and DRCA3. Mathematical investigation and numerical verification have revealed that DRCA2 is equivalent to the currently widely used cross-section adjustment method. Moreover, DRCA3 is found to be identical to the cross-section adjustment method based on MVUE, which has been proposed in the previous study.

Journal Articles

Development of design technique for vacuum insulation in large size multi-aperture multi-grid accelerator for nuclear fusion

Kojima, Atsushi; Hanada, Masaya; Tobari, Hiroyuki; Nishikiori, Ryo; Hiratsuka, Junichi; Kashiwagi, Mieko; Umeda, Naotaka; Yoshida, Masafumi; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.

Review of Scientific Instruments, 87(2), p.02B304_1 - 02B304_5, 2016/02

 Times Cited Count:11 Percentile:48.61(Instruments & Instrumentation)

Optimization techniques of the vacuum insulation design have been developed in order to realize a reliable voltage holding capability of Multi-Aperture Multi-Grid accelerators for giant negative ion sources for nuclear fusion. In this method, the nested multilayer configuration of each acceleration stage in the MAMuG accelerator can be uniquely designed to satisfy the target voltage within given boundary conditions. The evaluation of the voltage holding capabilities of each acceleration stages were based on the past experimental results of the area effect and the multi-aperture effect on the voltage holding capability. Moreover, total voltage holding capability of multi-stage was estimated by taking the multi-stage effect into account, which was experimentally obtained in this time. In this experiment, the multi-stage effect appeared as the superposition of breakdown probabilities in each acceleration stage, which suggested that multi-stage effect can be considered as the voltage holding capability of the single acceleration gap having the total area and aperture. The analysis on the MAMuG accelerator for JT-60SA agreed with the past gap-scan experiments with an accuracy of less than 10% variation.

Journal Articles

Long pulse acceleration of MeV class high power density negative H$$^{-}$$ ion beam for ITER

Umeda, Naotaka; Kojima, Atsushi; Kashiwagi, Mieko; Tobari, Hiroyuki; Hiratsuka, Junichi; Watanabe, Kazuhiro; Dairaku, Masayuki; Yamanaka, Haruhiko; Hanada, Masaya

AIP Conference Proceedings 1655, p.050001_1 - 050001_10, 2015/04

For ITER neutral beam system, negative deuterium ion beam of 1 MeV, 40 A (current density of 200 A/m$$^{2}$$) is required for 3600 s. To demonstrate ITER relevant negative ion beam acceleration, beam acceleration test has been carried out at MeV test facility in JAEA. The present target is H$$^{-}$$ ion beam acceleration up to 1 MeV with 200 A/m$$^{2}$$ for 60 s, which beam energy and pulse length are the present facility limit. To extend pulse duration time up to facility limit at high power density beam, new extraction grid has been developed with high cooling capability, which electron suppression magnet is placed under cooling channel. In addition, the aperture size of the electron suppression grid is enlarged from 14 mm to 16 mm and the aperture displacement is modified to reduce collision of negative ion beam on the grid. By these modifications, total grid power loading has reduced from 14% to 11%. As a result, beam acceleration up to 60 s which is the facility limit, has achieved at 700 kV, 100 A/m$$^{2}$$ of negative ion beam without breakdown.

JAEA Reports

Disassembly of the NBI system on JT-60U for JT-60 SA

Akino, Noboru; Endo, Yasuei; Hanada, Masaya; Kawai, Mikito*; Kazawa, Minoru; Kikuchi, Katsumi*; Kojima, Atsushi; Komata, Masao; Mogaki, Kazuhiko; Nemoto, Shuji; et al.

JAEA-Technology 2014-042, 73 Pages, 2015/02


According to the project plan of JT-60 Super Advanced that is implemented as an international project between Japan and Europe, the neutral beam (NB) injectors have been disassembled. The disassembly of the NB injectors started in November, 2009 and finished in January, 2012 without any serious problems as scheduled. This reports the disassembly activities of the NB injectors.

Journal Articles

FRP insulator column for high current accelerator of ITER; International thermonuclear experimental reactor

Inoue, Takashi

Kyoka Purasuchikkusu, 60(7), p.269 - 270, 2014/07

In ITER as a thermonuclear fusion experimental reactor being conducted by an international project, a large bore insulator ring of about 1.8 m in diameter is required for generation of 1 MeV, 40 A ion beam for plasma heating by Neutral Beam Injector. At JAEA, R&D has been carried out for development of such large bore insulator ring made of ceramics, and in parallel, ion beam experiments have been carried out with insulator rings made of FRP. The experiments have troubled with frequent high voltage breakdowns after outgas from FRP. Finding melt epoxy traces at triple junction (interface of vacuum, metal and FRP as dielectric material), local stress at the triple junction has been mitigated by mounting a large metal structure, so called stress ring. As a result, acceleration of 0.98 MeV, 185 A/m$$^{2}$$ hydrogen negative ion beam has successfully achieved in short pulses, where the requirement by ITER is 1 MeV and 200 A/m$$^{2}$$.

Journal Articles

Progress of neutral beam injection system on JT-60U for long pulse operation

Ikeda, Yoshitaka; NBI Heating Group; NCT Design Team

Journal of the Korean Physical Society, 49, p.S43 - S47, 2006/12

There are two type of NBI systems on JT-60U. One is the positive ion-based NBI (P-NBI) to inject the beam energy of 80-85 kV. The other is the negative ion-based NBI (N-NBI) at the beam energy more than 350 keV. Recently the pulse duration of NBI system was required to extend up to 30 sec so as to study long pulse plasmas. The four P-NBI units, which tangentially inject neutral beam to plasma, were modified to extend the pulse duration up to 30 sec with 2 MW/unit at $$sim$$ 85 keV. The seven P-NBI units, each of which perpendicularly injects for 10 sec, were conducted to operate in series for the total pulse duration of 30 sec. The ion source of the N-NBI unit was also modified to reduce the heat load of the grid for 30 sec operation. The pulse duration was extended up to 25 sec, $$sim$$ 1 MW at the beam energy of 350keV. In the next step, further pulse extension of NBI up to 100 sec is planned for the modified JT-60U with superconducting coils (so called NCT). This paper reports the recent progress of the NBI system on JT-60U and the design study of the upgraded NBI system for NCT.

Journal Articles

Present status of the negative ion based NBI system for long pulse operation on JT-60U

Ikeda, Yoshitaka; Umeda, Naotaka; Akino, Noboru; Ebisawa, Noboru; Grisham, L. R.*; Hanada, Masaya; Honda, Atsushi; Inoue, Takashi; Kawai, Mikito; Kazawa, Minoru; et al.

Nuclear Fusion, 46(6), p.S211 - S219, 2006/06

 Times Cited Count:59 Percentile:87.04(Physics, Fluids & Plasmas)

Recently, the extension of the pulse duration up to 30 sec has been intended to study quasi-steady state plasma on JT-60U N-NBI system. The most serious issue is to reduce the heat load on the grids for long pulse operation. Two modifications have been proposed to reduce the heat load. One is to suppress the beam spread which may be caused by beamlet-beamlet interaction in the multi-aperture grid due to the space charge force. Thin plates were attached on the extraction grid to modify the local electric field. The plate thickness was optimized to steer the beamlet deflection. The other is to reduce the stripping loss, where the electron of the negative ion beam is stripped and accelerated in the ion source and then collides with the grids. The ion source was modified to reduce the pressure in the accelerator column to suppress the beam-ion stripping loss. Up to now, long pulse injection of 17 sec for 1.6 MW and 25 sec for $$sim$$1 MW has been obtained by one ion source with these modifications.

Journal Articles

Development of a dc 1MV power supply technology for NB injectors

Watanabe, Kazuhiro; Kashiwagi, Mieko; Kawashima, Shuichi*; Ono, Yoichi*; Yamashita, Yasuo*; Yamazaki, Choji*; Hanada, Masaya; Inoue, Takashi; Taniguchi, Masaki; Okumura, Yoshikazu; et al.

Nuclear Fusion, 46(6), p.S332 - S339, 2006/06

 Times Cited Count:33 Percentile:72.40(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Characterization of Type-I ELMs in tangential co-, balanced- and counter-plus perpendicular NBI heated plasmas on JT-60U

Kamiya, Kensaku; Urano, Hajime; Koide, Yoshihiko; Takizuka, Tomonori; Oyama, Naoyuki; Kamada, Yutaka; JT-60 Team

Plasma Physics and Controlled Fusion, 48(5A), p.A131 - A139, 2006/05

 Times Cited Count:22 Percentile:58.55(Physics, Fluids & Plasmas)

Effects of plasma rotation and ripple loss on the Type-I ELMs have systematically studied in the JT-60U tokamak, scanning combinations of NBI at the three kinds of plasma volumes. New findings on the Type-I ELMs confirm to be smaller ELM energy loss per pedestal stored energy, DWELM/Wped, and faster ELM frequency, fELM, in the counter-NBI than co-NBI, keeping the power of ELM, PELM, per heating power crossing the separatrix, PSEP, constant. Balanced-NBI case is also intermediate between co- and counter-NBI. In addition, the product of PELM/PSEP decreases according to increase in the plasma volume, suggesting an increase in the inter-ELM transport due mainly to an enhancement in the ripple loss of fast ion.

Journal Articles

Acceleration of MeV-class energy, high-current-density H$$^{-}$$-ion beams for ITER neutral beam system

Taniguchi, Masaki; Inoue, Takashi; Kashiwagi, Mieko; Watanabe, Kazuhiro; Hanada, Masaya; Seki, Takayoshi*; Dairaku, Masayuki; Sakamoto, Keishi

Review of Scientific Instruments, 77(3), p.03A514_1 - 03A514_4, 2006/03

 Times Cited Count:15 Percentile:58.51(Instruments & Instrumentation)

In the ITER NB systems, conventional gas insulation technology cannot be utilized because of the conductivity of the insulation gas caused by the radiation from the tokamak plasma. To overcome this problem, a vacuum insulated beam source (VIBS), where the whole beam source is immersed in vacuum, has been developed in JAERI. Recently, voltage holding capability of the VIBS was drastically improved by installing the large stress ring and these progress enables us to perform the high power operation of the VIBS accelerator. For high current density H$$^{-}$$- beam acceleration, modifications were made on KAMABOKO source. At present, H$$^{-}$$- beam current density is 146 A/m$$^{2}$$ at 836 keV (input arc power; 40 kW, operation pressure; 0.3 Pa).The acceleration of 900 keV, 0.1 A level beam was accomplished for 175 shots during the test campaign. The beam acceleration was quite stable and the degradation of the voltage holding due to the beam acceleration and/or Cs seeding was not observed.

Journal Articles

Beam deflection by plasma grid filter current in the negative-ion source for JT-60U neutral beam injection system

Umeda, Naotaka; Ikeda, Yoshitaka; Hanada, Masaya; Inoue, Takashi; Kawai, Mikito; Kazawa, Minoru; Komata, Masao; Mogaki, Kazuhiko; Oga, Tokumichi

Review of Scientific Instruments, 77(3), p.03A529_1 - 03A529_3, 2006/03

 Times Cited Count:6 Percentile:33.89(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Design study of a neutral beam injector for fusion DEMO plant at JAERI

Inoue, Takashi; Hanada, Masaya; Kashiwagi, Mieko; Nishio, Satoshi; Sakamoto, Keishi; Sato, Masayasu; Taniguchi, Masaki; Tobita, Kenji; Watanabe, Kazuhiro; DEMO Plant Design Team

Fusion Engineering and Design, 81(8-14), p.1291 - 1297, 2006/02

 Times Cited Count:11 Percentile:60.07(Nuclear Science & Technology)

Requirement and technical issues of the neutral beam inejctor (NBI) is discussed for fusion DEMO plant. The NBI for the fusion DEMO plant should be high efficiency, high energy and high reliability with long life. From the view point of high efficiency, use of conventional electrostatic accelerator is realistic. Due to operation under radiation environment, vacuum insulation is essential in the accelerator. According to the insulation design guideline, it was clarified that the beam energy of 1.5$$sim$$2 MeV is possible in the accelerator. Development of filamentless, and cesium free ion source is required, based on the existing high current/high current density negative ion production technology. The gas neutralization is not applicable due to its low efficiency (60%). R&D on an advanced neutralization scheme such as plasma neutralization (efficiency: $$>$$80%) is required. Recently, development of cw high power semiconductor laser is in progress. The paper shows a conceptual design of a high efficiency laser neutralizer utilizing the new semiconductor laser array.

Journal Articles

Heating, current drive, and advanced plasma control in JFT-2M

Hoshino, Katsumichi; Yamamoto, Takumi; Tamai, Hiroshi; Oasa, Kazumi; Kawashima, Hisato; Miura, Yukitoshi; Ogawa, Toshihide; Shoji, Teruaki*; Shibata, Takatoshi; Kikuchi, Kazuo; et al.

Fusion Science and Technology, 49(2), p.139 - 167, 2006/02

 Times Cited Count:2 Percentile:17.06(Nuclear Science & Technology)

The main results obtained by the various heating and current drive systems, external coil system and divertor bias system are reviewed from the viewpoint of the advanced active control of the tokamak plasma. Also, the features of each system are described. The contribution of the JFT-2M in these areas are summarized.

Journal Articles

Deuterium depth profiling in JT-60U W-shaped divertor tiles by nuclear reaction analysis

Hayashi, Takao; Ochiai, Kentaro; Masaki, Kei; Goto, Yoshitaka*; Kutsukake, Chuzo; Arai, Takashi; Nishitani, Takeo; Miya, Naoyuki

Journal of Nuclear Materials, 349(1-2), p.6 - 16, 2006/02

 Times Cited Count:10 Percentile:56.85(Materials Science, Multidisciplinary)

Deuterium concentrations and depth profiles in plasma-facing graphite tiles used in the divertor of JT-60U were investigated by NRA. The highest deuterium concentration of D/$$^{12}$$C of 0.053 was found in the outer dome wing tile, where the deuterium accumulated probably through the deuterium-carbon co-deposition. In the outer and inner divertor target tiles, the D/$$^{12}$$C data were lower than 0.006. Additionally, the maximum (H+D)/$$^{12}$$C in the dome top tile was estimated to be 0.023 from the results of NRA and SIMS. OFMC simulation showed energetic deuterons caused by NBI were implanted into the dome region with high heat flux. Furthermore, the surface temperature and conditions such as deposition and erosion significantly influenced the accumulation process of deuterium. The deuterium depth profile, SEM observation and OFMC simulation indicated the deuterium was considered to accumulate through three processes: the deuterium-carbon co-deposition, the implantation of energetic deuterons and the deuterium diffusion into the bulk.

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:96 Percentile:93.19(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

Shielding design of the ITER NBI Duct for nuclear and bremsstrahlung radiation

Sato, Satoshi; Iida, Hiromasa; Yamauchi, Michinori*; Nishitani, Takeo

Radiation Protection Dosimetry, 116(1-4), p.28 - 31, 2005/12

 Times Cited Count:3 Percentile:24.15(Environmental Sciences)

no abstracts in English

Journal Articles

N-NBI heating and current drive in JT-60U towards steady-state tokamak

Ikeda, Yoshitaka; Oikawa, Toshihiro; Ide, Shunsuke

Purazuma, Kaku Yugo Gakkai-Shi, 81(10), p.773 - 778, 2005/10

In steady-state tokamak fusion reactors, an efficient external current drive and a large fraction of the bootstrap current are required for non-inductive operation at low circulating power. NBI is a powerful and reliable actuator for current drive and heating. A negative ion-based NBI (N-NBI) with a high beam energy more than 350 keV has been installed in the JT-60U tokamak in order to study the NBI current drive and heating in an ITER relevant regime. This paper presents recent progress of N-NBI experiments and its system in JT-60U towards steady-state operation for ITER and tokamak fusion reactors.

Journal Articles

Application of NBI technologies

Watanabe, Kazuhiro; Ando, Yasunori*

Purazuma, Kaku Yugo Gakkai-Shi, 81(10), p.792 - 797, 2005/10

no abstracts in English

268 (Records 1-20 displayed on this page)