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JAEA Reports

Characteristics of pore formers in low density MOX pellet fabrication

Mizuno, Mineo; Haga, Tetsuya; Sudo, Katsuo; Takeuchi, Kentaro; Okita, Takatoshi; Kihara, Yoshiyuki

JAEA-Technology 2011-009, 100 Pages, 2011/06

JAEA-Technology-2011-009.pdf:32.59MB

Crystalline cellulose granulated to sizes from 70 to 100 micron was previously used as pore former (PF) to fabricate low density MOX pellets for MONJU. When sale of Avicel was discontinued, it became necessary to find a substitute PF. Then, small scale fabrication tests of MOX pellets with candidate PFs were conducted. Three candidate PFs, cellulose beads, CEOLUS and CELPHERE, were examined in the tests. The results are summarized below. (1) The CELPHERE gave MOX pellets with almost same density depression performance as pellets using Avicel, and standards deviation of the sintered densities of pellets was the smallest. (2) MOX pellets with CELPHERE had lower incidence of observable defects. (3) MOX pellets with CELPHERE had almost the same O/M as pellets with Avicel. (4) MOX pellets with CELPHERE had lower incidence of micro cracks. (5) The densification amount of pellets with CELPHERE was almost the same as that of pellets with Avicel. It was concluded CELPHERE was a suitable substitute for Avicel.

Journal Articles

1 MV holding and beam optics in a multi-aperture multi-grid accelerator for ITER NBI

Kashiwagi, Mieko; Taniguchi, Masaki; Kojima, Atsushi; Dairaku, Masayuki; Hanada, Masaya; Hemsworth, R. S.*; Mizuno, Takatoshi*; Takemoto, Jumpei; Tanaka, Masanobu*; Tanaka, Yutaka*; et al.

Proceedings of 23rd IAEA Fusion Energy Conference (FEC 2010) (CD-ROM), 8 Pages, 2011/03

At JAEA, a multi-aperture multi-grid accelerator has been developed for the ITER neutral beam system. A target is H$$^{-}$$ ion beam acceleration of 0.5 A (200 A/m$$^{2}$$) at 1 MeV. In real accelerators, it was found that the voltage holding was about a half of that obtained in an ideal small electrode. After applying necessary gap length and radii of edges of grid supports to lower local electric field concentrations, the accelerator succeeded in sustaining 1 MV for 4000 s. As a result, beam parameters were increased to 879 keV, 0.36 A (157 A/m$$^{2}$$) at perveance matched condition from 796 kV, 0.32 A (140 A/m$$^{2}$$) reported in FEC2008. In the beam acceleration, the beamlet deflections due to magnetic field and space charge repulsion caused direct interceptions, that resulted in limitations in the beam energy and current. Compensation of these beamlet deflections has been tested applying aperture offset and field shaping plate, which were examined in a three-dimensional beam analysis.

Journal Articles

Three-dimensional analysis of beamlet deflection in a MeV accelerator for ITER NBI

Kashiwagi, Mieko; Taniguchi, Masaki; Umeda, Naotaka; Mizuno, Takatoshi; Tobari, Hiroyuki; Dairaku, Masayuki; Watanabe, Kazuhiro; Inoue, Takashi

Plasma and Fusion Research (Internet), 5, p.S2097_1 - S2097_4, 2010/12

An accelerator which generates deuterium negative ion beams of 1 MeV, 40 A for 3600 s is required for the ITER neutral beam injector (NBI). To realize such a high power accelerator, numerical studies have been carried out in parallel to acceleration tests in JAEA. After long pulse acceleration tests up to 30 s, it was found that parts of grid were melt around the grid apertures. In order to investigate how the grids melted, a three dimensional beam analysis was carried out in combination with 2D beam analysis code and gas flow code. The analysis clarified that the beamlet was deflected due to their own space charge repulsion and magnetic field at extraction grid, which led to direct interceptions of the beamlets at the grids. The power loads at the grid by these deflected beamlets were found to be more than 20 kW/cm$$^{2}$$. For next long pulse tests, a new extraction grid with aperture offset and field shaping plate has been designed so as to compensate the beamlet deflections.

Journal Articles

Heat loading of MeV accelerator grids during long pulse beam operation

Umeda, Naotaka; Mizuno, Takatoshi; Taniguchi, Masaki; Kashiwagi, Mieko; Ezato, Koichiro; Tobari, Hiroyuki; Dairaku, Masayuki; Watanabe, Kazuhiro; Sakamoto, Keishi; Inoue, Takashi

Journal of Plasma and Fusion Research SERIES, Vol.9, p.259 - 263, 2010/08

Long pulse acceleration of ITER class H$$^{-}$$ ion beam has carried out at MeV accelerator. Melts of the acceleration grids were found around grid apertures. To accelerate higher power beam, compensation of the beam deflection and design of a new grid which has high cooling performance is required. In this study, 3D thermal transport analysis was carried out and a new acceleration grid was designed. From the analysis, it was found that the grid temperature exceeded the melting point in a few seconds. To overcome this problem, a new acceleration grid was designed whose cooling channel was drilled near upper surface. This countermeasure is effective not only to reduce the temperature rise but to enlarge the aperture size from 14 mm to 16 mm. From the result of heat analysis, temperature rise of the new grid is greatly reduced than that of the previous grid. It is expected that higher power and longer pulse beam would be accelerated at next test campaign.

Journal Articles

Development of the high voltage bushing for the ITER NBI

Tobari, Hiroyuki; Inoue, Takashi; Dairaku, Masayuki; Umeda, Naotaka; Kashiwagi, Mieko; Taniguchi, Masaki; Mizuno, Takatoshi; Watanabe, Kazuhiro; Sakamoto, Keishi

Journal of Plasma and Fusion Research SERIES, Vol.9, p.152 - 156, 2010/08

The high voltage (HV) bushing in ITER NBI acts as a feed through for electric power and cooling water from the -1 MV power supply in pressurized SF$$_{6}$$ gas atmosphere to negative ion source / accelerator inside vacuum. The HV bushing has five-stage structure each of which consists of a large bore ceramic ring with 1.56 m in diameter as the insulator. The ceramic is metalized and brazed with Kovar plate and then metal flanges to form the vacuum boundary as a whole. However, there is no practical example of brazing with such a large ceramic. JAEA has successfully accomplished brazing of the world's largest ceramic with Kovar plate for the first time through sample tests and mechanical analyses. Following the result, manufacturing of a mock-up simulating one-stage of the HV bushing has been completed and its vacuum insulation test is now ongoing. Electric field design inside the HV bushing for -1 MV insulation is also ongoing. In this conference, recent progresses above are reported.

Journal Articles

Long pulse H$$^{-}$$ ion beam acceleration in MeV accelerator

Taniguchi, Masaki; Mizuno, Takatoshi; Umeda, Naotaka; Kashiwagi, Mieko; Watanabe, Kazuhiro; Tobari, Hiroyuki; Kojima, Atsushi; Tanaka, Yutaka; Dairaku, Masayuki; Hanada, Masaya; et al.

Review of Scientific Instruments, 81(2), p.02B101_1 - 02B101_3, 2010/02

 Times Cited Count:7 Percentile:60.46(Instruments & Instrumentation)

A Multi-Aperture Multi-Grid (MAMuG) accelerator called "MeV accelerator" has been developed for neutral beam injection (NBI) system of ITER. The MeV accelerator succeeded in accelerating 796 keV, 320 mA H$$^{-}$$ ion beam until 2007. However, pulse length was limited to 0.2 s due to un-cooled grids. In the present work, long pulse H$$^{-}$$ ion beam acceleration was performed by the MeV accelerator equipped with water-cooled new grids. The H$$^{-}$$ ion current was increased step by step at certain energy with seeding Cs up to the optimum perveance. At present, pulse length was extended to 5 s for 750 keV, 221 mA (perveance match) and maximum power of 1.01 MJ was achieved (650 keV, 163 mA, 10s). At higher energy and current, pulse length was limited by breakdowns between the grids. This was due to high heat load on A3G and GRG grid by deflection of H$$^{-}$$ ion beam.

Journal Articles

Analysis of secondary particle behavior in multiaperture, multigrid accelerator for the ITER neutral beam injector

Mizuno, Takatoshi; Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Tobari, Hiroyuki; Watanabe, Kazuhiro; Dairaku, Masayuki; Sakamoto, Keishi; Inoue, Takashi

Review of Scientific Instruments, 81(2), p.02B103_1 - 02B103_3, 2010/02

 Times Cited Count:3 Percentile:79.14(Instruments & Instrumentation)

For a neutral beam injector (NBI) of ITER, the negative ion accelerator capable of 1 MeV, 40 A negative ion beam acceleration for up to 3,600 s is required. Suppression of heat load onto acceleration grids is a key issue for the long pulse acceleration of negative ion beams. A major source of the heat load will be from incident of secondary particles, which are neutrals, positive ions and electrons, on the grids. The complicated behavior of secondary particles in the MeV accelerator of JAEA is analyzed using the Electrostatic Accelerator Mote Carlo Code (EAMCC) developed by CEA. Water-cooled new grids were equipped with the MeV accelerator for the long pulse H$$^{-}$$ ion beam acceleration and second acceleration grid (A2G) was removed for simplification. Analytical results for 600 keV H$$^{-}$$ beam acceleration show that the heat load of third acceleration grid (A3G) is inevitably high because of lack of upstream grid, i.e., A2G.

Journal Articles

3D modeling of the electron energy distribution function in negative hydrogen ion sources

Terasaki, Ryo*; Fujino, Ikuro*; Hatayama, Akiyoshi*; Mizuno, Takatoshi; Inoue, Takashi

Review of Scientific Instruments, 81(2), p.02A703_1 - 02A703_3, 2010/02

 Times Cited Count:19 Percentile:31.08(Instruments & Instrumentation)

In order to develop the large H$$^{-}$$ ion source for future fusion reactors, the uniform production of H$$^{-}$$ ions is one of the important issues. Recently, it has been shown experimentally in JAEA 10A negative ion source that the non-uniformity of the electron energy distribution function (EEDF) inside the source and the resultant non-uniformity of the H$$^{-}$$ production strongly affect the H$$^{-}$$ beam optics. Therefore, modeling of the EEDF and analysis of the spatial non-uniformity of the EEDF is necessary to optimize H$$^{-}$$ ion source and the beam optics. For this purpose, we are developing the 3D3V Monte Carlo modeling of the EEDF in realistic 3D geometry. The code reproduces the spatial non-uniformity of the EEDF observed in the experiments. Our developing code is a powerful tool for the design of the next generation sources.

Journal Articles

Analyses of high power negative ion accelerators for ITER neutral beam injector

Kashiwagi, Mieko; Taniguchi, Masaki; Dairaku, Masayuki; Grisham, L.*; Hanada, Masaya; Mizuno, Takatoshi; Tobari, Hiroyuki; Umeda, Naotaka; Watanabe, Kazuhiro; Sakamoto, Keishi; et al.

Review of Scientific Instruments, 81(2), p.02B113_1 - 02B113_5, 2010/02

 Times Cited Count:5 Percentile:69.1(Instruments & Instrumentation)

In JAEA, a multi aperture and multi grid accelerator has been tested for ITER NBI. In recent experiments, it was shown that the acceleration gaps (1st/2nd/3rd/4th/5th gap) have to be expanded from 104/94/87/78/72 in the original to all 100 mm to sustain 200 kV in each stage stably, and 1 MV in total. On the contrary, increases of beam divergence, stripping loss of negative ions and beamlet deflections due to space charge repulsion among beamlets could appear as issues due to the longer gaps. Beam divergence and stripping loss of ions have been examined in a 2D beam optics study utilizing BEAMORBT code and 3D gas flow code, respectively. Beamlet deflections have been examined in a 3D multi beamlet analysis utilizing OPERA-3d code. As results of these simulations, it was clarified that the gap length could be expanded up to 120 mm. This results were applied to design of the accelerator with the long gap of 120 mm.

JAEA Reports

Behavior of secondary-particles in a MeV-class electrostatic accelerator

Mizuno, Takatoshi; Inoue, Takashi; Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Tobari, Hiroyuki; Dairaku, Masayuki; Watanabe, Kazuhiro

JAEA-Research 2008-120, 19 Pages, 2009/03

JAEA-Research-2008-120.pdf:5.24MB

In an accelerator for a N-NBI, there are several processes of secondary-particle production such as the collision of H$$^-$$ ions with H$$_2$$ gas, extraction of H$$_{2}^{+}$$ ions from beam plasma, and secondary-electron emission. The secondary particles cause heat load to the NBI components. It is necessary to analyze behavior of them in the accelerator. In this report, the secondary-particle behavior in MAMuG type MeV accelerator at JAEA has been analyzed by EAMCC. In the result, it is clarified that about 40% of H$$^-$$ ions extracted from the ion source were lost by the stripping process in the MeV accelerator. More than 90% of the heat load to the intermediate grids was caused by collision of the electrons. A comparison of results obtained from experiments and present analyses showed different tendency in the currents flowing into the 2nd and the 3rd intermediate grids. This is supposed due to H$$_{2}^{+}$$ ions extracted from beam plasma as a possible cause of the difference.

Journal Articles

Numerical analysis of the hydrogen atom density in a negative ion source

Takato, Naoyuki; Hanatani, Junji*; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Tobari, Hiroyuki; Hanada, Masaya; Inoue, Takashi; Taniguchi, Masaki; Dairaku, Masayuki; Kashiwagi, Mieko; et al.

AIP Conference Proceedings 925, p.38 - 45, 2007/09

The production and transport processes of the H$$^0$$ atom are numerically simulated to obtain the H$$^0$$ atom density. The three dimensional transport code using the Monte Carlo method has been applied to H$$^0$$ atoms in the large "JAEA 10 ampere negative ion source" under the Cs-seeded condition. In this study, the production rate of H$$^0$$ atoms through the dissociation process of H$$_2$$ molecules is estimated from single probe characteristics of the Langmuir probe measurement. In addition, the energy relaxation process of H$$^0$$ atoms is also considered. The results show that the existence of high-energy electrons and the energy relaxation process of H$$^0$$ atoms affect the H$$^0$$ atom density.

Journal Articles

The Origin of beam non-uniformity in a large Cs-seeded negative ion source

Hanada, Masaya; Seki, Takayoshi*; Takado, Naoyuki; Inoue, Takashi; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Taniguchi, Masaki; Watanabe, Kazuhiro

Nuclear Fusion, 46(6), p.S318 - S323, 2006/06

 Times Cited Count:28 Percentile:27.55(Physics, Fluids & Plasmas)

The origin of the beam non-uniformity, that is one of the key issues in large Cs-seeded negative ion sources for JT-60U and ITER, was experimentally examined by measuring correlations between the intensity of the H$$^{-}$$ ion beam and plasma parameters such as an electron temperature and plasma density in the JAERI 10 A negative ion source. From the correlation between the beam intensity and the plasma parameters, it was foreseen that the beam non-uniformity was due to the localization of the plasma and/or H0 atoms caused by B x $$nabla$$B drift of the fast electron from filaments. The filament position was modified to suppress the B x $$nabla$$B drift, and then the spatial uniformity of the beam intensity was examined. By this modification, the root-mean-square deviation of the spatial beam intensity from the averaged value deceased to a half of that before modification while the beam intensity integrated along the longitudinal direction was kept to be constant. From this result, it was confirmed that one of the origin of the beam non-uniformity was caused by plasma localization.

Journal Articles

Improvement of beam uniformity by magnetic filter optimization in a Cs-seeded large negative-ion source

Hanada, Masaya; Seki, Takayoshi*; Takado, Naoyuki*; Inoue, Takashi; Tobari, Hiroyuki; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Dairaku, Masayuki; Kashiwagi, Mieko; Sakamoto, Keishi; et al.

Review of Scientific Instruments, 77(3), p.03A515_1 - 03A515_3, 2006/03

 Times Cited Count:23 Percentile:26.04(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Numerical analysis of the spatial nonuniformity in a Cs-seeded H$$^{-}$$ ion source

Takado, Naoyuki*; Hanatani, Junji*; Mizuno, Takatoshi*; Kato, Kyohei*; Hatayama, Akiyoshi*; Hanada, Masaya; Seki, Takayoshi; Inoue, Takashi

Review of Scientific Instruments, 77(3), p.03A533_1 - 03A533_3, 2006/03

 Times Cited Count:14 Percentile:39.52(Instruments & Instrumentation)

Surface production and transport process of H$$^{-}$$ ions are numerically simulated to clarify the origin of H$$^{-}$$ beam non-uniformity. A three-dimensional transport code using Monte Carlo method has been applied to productions of H$$^{0}$$ atoms and H$$^{-}$$ ions in a large negative ion source under the Cs seeded condition. The results show that a large fraction of hydrogen atoms are produced in a high electron temperature region. This leads to a spatial non-uniformity of H$$^{0}$$ atom flux to the plasma grid where H$$^{0}$$ atoms capture electrons and converted to H$$^{-}$$ ions. In addition, most surface-produced H$$^{-}$$ ions are extracted even through the high electron temperature region without destruction.

Journal Articles

Experimental study on spatial uniformity of H$$^{-}$$ ion beam in a large negative ion source

Hanada, Masaya; Seki, Takayoshi*; Takado, Naoyuki*; Inoue, Takashi; Morishita, Takatoshi; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; et al.

Fusion Engineering and Design, 74(1-4), p.311 - 317, 2005/11

 Times Cited Count:7 Percentile:51.21(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Numerical analysis of plasma spatial uniformity in negative ion sources by a fluid model

Mizuno, Takatoshi*; Kitade, Yuki*; Hatayama, Akiyoshi*; Sakurabayashi, Toru*; Imai, Naoki*; Morishita, Takatoshi; Inoue, Takashi

Review of Scientific Instruments, 75(5), p.1760 - 1763, 2004/05

 Times Cited Count:7 Percentile:57.87(Instruments & Instrumentation)

Spatial non-uniformities of extracted negative ion beam were observed experimentally in tandem-type negative ion sources. To improve the beam uniformity, it is important to analyze the plasma profile in the ion source including magnetic filter effect. In the filter region, Lorentz force is important for both ions and electrons. However, their dynamics are completely different, i.e. electrons are magnetized and ions are not magnetized. Then, the system of two-dimensional two-fluid model equations is solved simultaneously to obtain self-consistent profiles of the plasma parameters. The result shows that a possible cause of spatial non-uniformity is the ion flow rather than ExB drift motion of electrons. This flow of ions is caused by synergetic effect of the force by electric field, Lorentz force and inertia force. To verify the results above and more quantitative comparisons with experiments, full 3D analysis is needed, because the electron loss along the field line is important for the plasma potential and the electric field in the filter region. Full 3D analysis is now in progress.

Oral presentation

Dependence of the beam uniformity on the magnetic filter strength in a large Cs-seeded negative ion source for ITER

Seki, Takayoshi; Hanada, Masaya; Tobari, Hiroyuki; Inoue, Takashi; Takado, Naoyuki*; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Kashiwagi, Mieko; Taniguchi, Masaki; Watanabe, Kazuhiro; et al.

no journal, , 

no abstracts in English

Oral presentation

Improvement of beam uniformity in a Cs-seeded large negative ion source

Seki, Takayoshi; Hanada, Masaya; Tobari, Hiroyuki; Inoue, Takashi; Kashiwagi, Mieko; Taniguchi, Masaki; Watanabe, Kazuhiro; Sakamoto, Keishi; Takado, Naoyuki*; Mizuno, Takatoshi*; et al.

no journal, , 

no abstracts in English

Oral presentation

Numerical analysis of the production profile for hydrogen atoms and negative ions in a Cs-seeded large negative ion source

Takato, Naoyuki; Hanatani, Junji*; Kato, Kyohei*; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Tobari, Hiroyuki; Hanada, Masaya; Inoue, Takashi; Taniguchi, Masaki; Hasebe, Mieko; et al.

no journal, , 

no abstracts in English

Oral presentation

Numerical analysis of secondary-particle behavior in MeV-class accelerator for ITER NBI

Mizuno, Takatoshi; Inoue, Takashi; Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Tobari, Hiroyuki; Watanabe, Kazuhiro; Dairaku, Masayuki; Sakamoto, Keishi

no journal, , 

no abstracts in English

23 (Records 1-20 displayed on this page)