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JAEA Reports

Assessment report of research and development activities in FY2014; Activity "Fusion Research and Development" (In-advance evaluation)

Fusion Research and Development Directorate

JAEA-Evaluation 2016-002, 40 Pages, 2016/03

JAEA-Evaluation-2016-002.pdf:2.66MB

Japan Atomic Energy Agency (hereinafter referred to as "JAEA") asked the assessment committee, "Evaluation Committee of Research and Development Activities for Fusion" (hereinafter referred to as "Committee") for in-advance evaluation of "Research and Development of the technical system for extraction of fusion energy," in accordance with "General Guideline for the Evaluation of Government R&D Activities" by Cabinet Office, Government of Japan, "Guideline for Evaluation of R&D in Ministry of Education, Culture, Sports, Science and Technology" and "Regulation on Conduct for Evaluation of R&D Activities" by JAEA. In response to the JAEA's request, the Committee assessed the research program of the Fusion Research and Development Directorate (hereinafter referred to as "FRDD") during the period from April 2015 to March 2022. The Committee evaluated the management and research activities of the FRDD based on the explanatory documents prepared by the FRDD, the oral presentations with questions-and-answers by the Director General and the Deputy Director Generals.

JAEA Reports

Assessment report of research and development activities in FY2014; Activity "Fusion Research and Development" (Result evaluation)

Fusion Research and Development Directorate

JAEA-Evaluation 2016-001, 128 Pages, 2016/03

JAEA-Evaluation-2016-001.pdf:33.25MB

Japan Atomic Energy Agency (hereinafter referred to as "JAEA") asked the assessment committee, "Evaluation Committee of Research and Development Activities for Fusion" (hereinafter referred to as "Committee") for result evaluation of "Research and Development of the Technical System for Extraction of Fusion Energy," in accordance with "General Guideline for the Evaluation of Government R&D Activities" by Cabinet Office, Government of Japan, "Guideline for Evaluation of R&D in Ministry of Education, Culture, Sports, Science and Technology " and "Regulation on Conduct for Evaluation of R&D Activities" by JAEA. In response to the JAEA's request, the Committee assessed the research program of the Fusion Research and Development Directorate (hereinafter referred to as "FRDD") during the period from April 2010 to November 2014. The Committee evaluated the management and research activities of the FRDD based on the explanatory documents prepared by the FRDD, the oral presentations with questions-and-answers by the Director General and the Deputy Director Generals.

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:5 Percentile:59.87(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

Progress in long-pulse production of powerful negative ion beams for JT-60SA and ITER

Kojima, Atsushi; Umeda, Naotaka; Hanada, Masaya; Yoshida, Masafumi; Kashiwagi, Mieko; Tobari, Hiroyuki; Watanabe, Kazuhiro; Akino, Noboru; Komata, Masao; Mogaki, Kazuhiko; et al.

Nuclear Fusion, 55(6), p.063006_1 - 063006_9, 2015/06

 Times Cited Count:28 Percentile:8.37(Physics, Fluids & Plasmas)

Significant progresses in the extension of pulse durations of powerful negative ion beams have been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long pulse production/acceleration of negative ion beams in JT-60SA and ITER, the new technologies have been developed in the JT-60SA ion source and the MeV accelerator in Japan Atomic Energy Agency. As for the long pulse production of high-current negative ions for JT-60SA ion source, the pulse durations have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA ion source, which satisfies the required pulse duration of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform negative ion productions with the modified tent-shaped filter field configuration. Moreover, the each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER ion source because the sustainment of the cesium coverage in large extraction area is one of the common issues between JT-60SA and ITER. As for the long pulse acceleration of high power density beams in the MeV accelerator for ITER, the pulse duration of MeV-class negative ion beams has been extended by more than 2 orders of magnitude by modifying the extraction grid with a high cooling capability and a high-transmission of negative ions. A long pulse acceleration of 60 s has been achieved at 70 MW/m$$^{2}$$ (683 keV, 100 A/m$$^{2}$$) which has reached to the power density of JT-60SA level of 65 MW/m$$^{2}$$.

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.

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

Long-pulse beam acceleration of MeV-class H$$^{-}$$ ion beams for ITER NB accelerator

Umeda, Naotaka; Kashiwagi, Mieko; Taniguchi, Masaki; Tobari, Hiroyuki; Watanabe, Kazuhiro; Dairaku, Masayuki; Yamanaka, Haruhiko; Inoue, Takashi; Kojima, Atsushi; Hanada, Masaya

Review of Scientific Instruments, 85(2), p.02B304_1 - 02B304_3, 2014/02

 Times Cited Count:10 Percentile:46.97(Instruments & Instrumentation)

In order to realize neutral beam systems in ITER whose target is to produce D$$^{-}$$ ion beam of 1 MeV, 200 A/m$$^{2}$$ during 3600s, the electrostatic five-stages negative ion accelerator has been developed at JAEA. To extend pulse length, heat load of the acceleration grids was reduced by controlling the ion beam trajectory. Namely, the beam deflection due to the residual magnetic filter in the accelerator was suppressed with the newly developed extractor with a 0.5 mm off-set aperture displacement. The use of new extractor improved the deflection angle from 6 mrad to 1 mrad, resulting in the reduction of direct interception of negative ions from 23% to 15% of the total acceleration power, respectively. As a result, the pulse length of 130 A/m$$^{2}$$, 881 keV H$$^{-}$$ ion beam has been successfully extended from a previous value of 0.4s to 8.7s.

Journal Articles

Compensations of beamlet deflections for 1 MeV accelerator of ITER NBI

Kashiwagi, Mieko; Taniguchi, Masaki; Umeda, Naotaka; Dairaku, Masayuki; Tobari, Hiroyuki; Yamanaka, Haruhiko; Watanabe, Kazuhiro; Inoue, Takashi; DeEsch, H. P. L.*; Grisham, L. R.*; et al.

AIP Conference Proceedings 1515, p.227 - 236, 2013/02

 Times Cited Count:8 Percentile:4.63

In a five stage multi-aperture multi-grid (MAMuG) accelerator for the ITER neutral beam injector (NBI), 1 MeV, 40 A D$$^-$$ ion beam is required for 1 hour. However, beamlets are deflected due to (1) magnetic field for electron suppression and (2) space charge repulsion between beamlets, and consequently, cause excess grid heat load. A three dimensional beam analysis has been carried out to compensate the beamlet deflections. This paper shows that the beamlet deflections due to (1) and (2) are compensated by an aperture offset of only 0.6 mm applied to the aperture of 17 mm in diameter in the extractor and by a metal bar attached around aperture area beneath the extractor, respectively. When the metal bar is increased to 3 mm in thickness and installed 30 mm away from the aperture area, the beamlet is steered gently by the weaker electric field distortion. The beam optics was confirmed not deteriorated by those compensations. The presentation also discusses application of these compensation techniques to the ITER design.

Journal Articles

Analysis of electron temperature distribution by kinetic modeling of electron energy distribution function in JAEA 10 ampere negative ion source

Shibata, Takanori; Terasaki, Ryo*; Kashiwagi, Mieko; Inoue, Takashi; Dairaku, Masayuki; Taniguchi, Masaki; Tobari, Hiroyuki; Umeda, Naotaka; Watanabe, Kazuhiro; Sakamoto, Keishi; et al.

AIP Conference Proceedings 1515, p.177 - 186, 2013/02

 Times Cited Count:8 Percentile:4.63

In the neutral beam injector in JT-60SA, one of issues is that negative ion beam is partially intercepted at acceleration grids due to a spatial non-uniformity of negative ion production on large extraction area (0.9$$times$$0.45m$$^{2}$$). Previous experiments showed that fast electrons emitted from filament cathodes are transported in a longitudinal direction by $$mathbf{B} times textrm{grad} mathbf{B}$$ drift and the spatial distribution of electron temperature ($$T_e$$) strongly relates with the non-uniformity. In this study, a three-dimensional electron transport analysis has been developed. Electron temperature in the analysis agreed well with measurements in JAEA 10A ion source. This study clarified that the bias of $$T_e$$ distribution are caused by the following reasons; (1) fast electrons drifted in the longitudinal direction survives near the end wall with energy up to $$E$$ = 25-60 eV and (2) they produces thermal electrons by collision with plasma particles there.

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:68.04(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

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

Nuclear fusion reactor

Inoue, Takashi

Purazuma, Kaku Yugo Gakkai-Shi, 87(Suppl.), p.179 - 185, 2011/02

This article is a part of text book for fusion reactor design aiming at a tokamak DEMO reactor. It has been identified that the NB system should be characterized by high efficiency, high energy, high reliability in year-long steady operation, and low maintenance frequency. Due to operation under radiation environment, vacuum insulation is essential in the accelerator. According to the vacuum insulation characteristics, it was clarified that a beam energy of 1.0-1.5 MeV is realistic. Development of filamentless, and cesium free ion source is required to achieve low maintenance frequency, based on the existing negative ion production technology. The gas neutralization is not applicable due to its low efficiency (60%). 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

Overview of the TBM R&D activities in Japan

Akiba, Masato; Enoeda, Mikio; Tanaka, Satoru*

Fusion Engineering and Design, 85(10-12), p.1766 - 1771, 2010/12

 Times Cited Count:12 Percentile:30.87(Nuclear Science & Technology)

As the primary candidate of ITER Test Blanket Module (TBM) for the first day of ITER operation, development of Water Cooled Solid Breeder (WCSB) TBM has been performed toward the TBM milestones, which are necessary for acceptance of the TBM in ITER for testing from the first day of plasma operation. Regarding the liquid breeder blanket development, universities and NIFS are conducting the development. This paper overviews the recent achievements of the TBMs and DEMO blankets.

Journal Articles

Progress of design and R&D of water cooled solid breeder test blanket module

Tsuru, Daigo; Enoeda, Mikio; Hirose, Takanori; Tanigawa, Hisashi; Ezato, Koichiro; Yokoyama, Kenji; Dairaku, Masayuki; Seki, Yohji; Suzuki, Satoshi; Mori, Kensuke*; et al.

Fusion Science and Technology, 56(2), p.875 - 882, 2009/08

 Times Cited Count:7 Percentile:49.61(Nuclear Science & Technology)

As the primary candidate of ITER Test Blanket Module (TBM) for the first day of ITER operation, development of Water Cooled Solid Breeder (WCSB) TBM has been performed toward the TBM milestones, which are necessary for acceptance of the TBM in ITER for testing from the first day of plasma operation. Milestones of ITER TBMs prior to the installation consist of milestones on safety assessment, module qualification and design integration in ITER. This paper overviews the recent achievements for preparation of the WCSB TBM for ITER day-1 operation, toward the TBM milestones.

Journal Articles

Status of the ITER heating neutral beam system

Hemsworth, R. S.*; Decamps, H.*; Graceffa, J.*; Schunke, B.*; Tanaka, Masanobu*; Dremel, M.*; Tanga, A.*; DeEsch, H. P. L.*; Geli, F.*; Milnes, J.*; et al.

Nuclear Fusion, 49(4), p.045006_1 - 045006_15, 2009/04

 Times Cited Count:328 Percentile:0.2(Physics, Fluids & Plasmas)

The ITER neutral beam (NB) injectors are the first injectors that will be operated under conditions and constraints similar to those in a fusion reactor. These injectors will be operated in a radiation environment and they will be activated due to the neutron flux from ITER. The injectors uses a single large ion source and accelerator that will produce 40 A 1 MeV D$$^{-}$$ beams for pulse lengths of up to 3600 s. Design changes have been made to the ITER NB injectors over the past 4 years as follows: (1) Modifications to allow installation and maintenance of the beamline components with an overhead crane. (2) The RF driven negative ion source has replaced the filamented ion source. (3) The ion source power supplies will be located in an air insulated high voltage (-1 MV) deck located outside the tokamak building instead of inside an SF6 insulated HV deck located above the injector. This paper describes the status of the design as of December 2008 including the above mentioned changes.

Journal Articles

Critical heat flux experiments using a screw tube under DEMO divertor-relevant cooling conditions

Ezato, Koichiro; Suzuki, Satoshi; Dairaku, Masayuki; Akiba, Masato

Fusion Engineering and Design, 83(7-9), p.1097 - 1101, 2008/12

 Times Cited Count:6 Percentile:55.23(Nuclear Science & Technology)

As part of development of Plasma-Facing Components (PFCs) for fusion machines, JAEA has been developing high performance cooling tubes with pressurized water flow. Along this line, a cooling tube with a helical triangular fin on its inner surface has been proposed recently for application to a fusion DEMO to enhance heat removal. Since the fin can be machined by a simple mechanical threading, this tube is called as a screw tube. Divertor cooling conditions in the DEMO design in JAEA are envisaged at the pressure of 4 MPa and the outlet temperature of 200$$^{circ}$$C to improve thermal efficiency of power generation. In the this study, effect of subcooling on critical heat flux (CHF) of the screw tube has been investigated under DEMO-relevant condition with the local pressure of 4 MPa and the inlet coolant temperature up to 180$$^{circ}$$C. A test sample is the screw tube made of pure Cu instead of F82H, a candidate material of the DEMO divertor. The results show that the ICHF values of the screw tube remains more than double values of the smooth at the inlet coolant temperature of 180$$^{circ}$$C, although temperature rise of the cooling water with 140 K leads to reduction of ICHF by almost half compared with those values at room temperature.

Journal Articles

Research and development of a super fast reactor, 8; Heat transfer experiments around a simulated fuel rod with supercritical pressure water

Ezato, Koichiro; Akiba, Masato; Enoeda, Mikio; Suzuki, Satoshi; Seki, Yohji; Tanigawa, Hisashi; Tsuru, Daigo; Mori, Hideo*; Oka, Yoshiaki*

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

no abstracts in English

Journal Articles

Research and development on plasma facing components for fusion reactors in JAEA

Suzuki, Satoshi; Ezato, Koichiro; Yokoyama, Kenji; Dairaku, Masayuki; Enoeda, Mikio; Tanigawa, Hisashi; Tsuru, Daigo; Seki, Yohji; Mori, Kensuke*; Nishi, Hiroshi; et al.

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

This paper presents the present status of R&D activities on plasma facing components (PFCs) for fusion reactors, such as ITER and fusion demonstration reactor (DEMO). The PFCs as typified by divertor and first wall components are subjected to high heat flux and particle flux from fusion plasma. It is essential to have sufficient heat removal capability and robust structure against those loadings. JAEA has been carried out to develop the ITER-PFCs which consist of copper alloys and armor materials with high thermal conductivity, such as carbon fiber composites, tungsten and beryllium. The demonstration of the thermomechanical performance has successfully been made under close mutual cooperation between the participant countries of ITER. Currently, the activity on the development of the ITER-PFCs is in a qualification phase prior to the bulk production for construction. In JAEA, the R&Ds on the DEMO-PFCs is being made in parallel with the development activity of the ITER-PFCs.

JAEA Reports

Spatial uniformity of negative ion beam in magnetically filtered hydrogen negative ion source; Effect of the H$$^{-}$$ ion production and transport processes on the H$$^{-}$$ ion beam intensity profile in the Cs-seeded negative ion source (Joint research)

Takato, Naoyuki; Tobari, Hiroyuki; Inoue, Takashi; Hanada, Masaya; Seki, Takayoshi*; Kato, Kyohei*; Hatayama, Akiyoshi*; Sakamoto, Keishi

JAEA-Research 2008-031, 44 Pages, 2008/03

JAEA-Research-2008-031.pdf:4.05MB

The origin of the H$$^{-}$$ ion beam non-uniformity under the Cesium seeded condition was studied in the JAEA 10 Ampere negative ion source by measuring the profiles of the beam intensity and plasma parameters. The numerical analyses, such as the trace of particles (the electron, the H$$^{0}$$ atom and the H$$^{-}$$ ion) trajectories using the Monte Carlo method, were also applied to consider the experimental results.

Journal Articles

Negative ion production in cesium seeded high electron temperature plasmas

Inoue, Takashi; Tobari, Hiroyuki; Takado, Naoyuki*; Hanada, Masaya; Kashiwagi, Mieko; Hatayama, Akiyoshi*; Wada, Motoi*; Sakamoto, Keishi

Review of Scientific Instruments, 79(2), p.02C112_1 - 02C112_4, 2008/02

 Times Cited Count:1 Percentile:90.35(Instruments & Instrumentation)

In experiments on uniformity improvement in a large negative ion source, steep gradients have been observed in the profiles of electron temperature and H$$^{-}$$ ion beam intensity. It has been observed that the gradient in the H$$^{-}$$ ion beam intensity is altered by seeding Cesium, though the electron temperature distribution is not affected by the Cs. Thus in the Cs seeded condition, the H$$^{-}$$ ion beam intensity is enhanced in local area illuminated by high-electron temperature plasmas. A brief analysis suggests possible advantages of high-electron temperature plasmas for the negative ion surface production, by enhancement of dissociation to yield proton or atoms as parent particles of the negative ions.

39 (Records 1-20 displayed on this page)