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Journal Articles

Evaluation of dark current profile for prediction of voltage holding capability on multi-aperture multi-grid accelerator for ITER

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

Plasma and Fusion Research (Internet), 11, p.2401014_1 - 2401014_4, 2016/03

One of critical issues for high-energy high-current beam acceleration in ITER and JT-60SA is the high voltage holding which is dominated by vacuum discharges. The past results suggest that vacuum discharge occurs beyond the threshold of the dark current. The dark current can be derived from F-N theory where electric field enhancement factor beta is included. Though, beta could only be evaluated from the experiment previously. Therefore, the method to decide beta without experiment is required. This time dark currents were measured at three different areas to compare beta in different electric field. As a result, the effective electric field $$beta$$E, where E is average electric field, were found to be almost constant for different areas although the beta is largely different. By applying $$beta$$E, beta can be evaluated analytically, leading to the analytical prediction of the dark current and voltage holding capability without the measurements.

Journal Articles

Measurement of heat load density profile on acceleration grid in MeV-class negative ion accelerator

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

Review of Scientific Instruments, 87(2), p.02B137_1 - 02B137_3, 2016/02

 Times Cited Count:3 Percentile:18.16(Instruments & Instrumentation)

To understand the physics of the negative ion extraction/acceleration, the heat load density profile on the acceleration grid has been firstly measured in the ITER prototype accelerator where the negative ions are accelerated to 1 MeV with five acceleration stages. In order to clarify the profile, the peripheries around the apertures on the acceleration grid were separated into thermally insulated 34 blocks with thermocouples. The spatial resolution is as low as 3 mm and small enough to measure the tail of the beam profile with a beam diameter of 16 mm. It was found that there were two peaks of heat load density around the aperture. These two peaks were also clarified to be caused by the intercepted negative ions and secondary electrons from detailed investigation by changing the beam optics and gas density profile. This is the first experimental result, which is useful to understand the trajectories of these particles.

Journal Articles

Time evolution of negative ion profile in a large cesiated negative ion source applicable to fusion reactors

Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Umeda, Naotaka; Hiratsuka, Junichi; Ichikawa, Masahiro; Watanabe, Kazuhiro; Grisham, L. R.*; Tsumori, Katsuyoshi*; et al.

Review of Scientific Instruments, 87(2), p.02B144_1 - 02B144_4, 2016/02

 Times Cited Count:8 Percentile:42.75(Instruments & Instrumentation)

Time evolution of spatial profile of negative ion production during an initial conditioning phase has been experimentally investigated in the JT-60 negative ion source. Up to 0.4 g Cs injection, there is no enhancement of the negative ion production and no observation of the Cs emission signal in the source, suggesting the injected Cs is mainly deposited on the water-cooled wall near the nozzle. After 0.4 g Cs injection, enhancement of the negative ion production appeared only at the central segment of the PG. The calculation of the Cs neutral/ion trajectories implied that a part of Cs was ionized near the nozzle and was transported to this area. The expansion of the area of the surface production was saturated after ~2 g Cs injection corresponding to 6000 s discharge time. From the results, it is found that Cs ionization and its transport plays an important role for the negative ion production.

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:9 Percentile:46.38(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

Development of the negative ion beams relevant to ITER and JT-60SA at Japan Atomic Energy Agency

Hanada, Masaya; Kojima, Atsushi; 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.02B322_1 - 02B322_4, 2016/02

 Times Cited Count:11 Percentile:52.68(Instruments & Instrumentation)

In International Thermo-nuclear Experimental Reactor (ITER) and JT-60 Super Advanced (JT-60 SA), the D$$^{-}$$ ion beams of 1 MeV, 40 A and 0.5 MeV, 22 A are required to produce 3600 s and 100 s for the neutral beam injection, respectively. In order to realize such as powerful D$$^{-}$$ ion beams for long duration time, Japan Atomic Energy Agency (JAEA) has energetically developed cesium (Cs)-seeded negative ion sources (CsNIS) and electro-static multi-aperture and multi-stage accelerators (MAMuG accelerator) which are chosen as the reference design of ITER and JT-60 SA. In the development of the CsNIS, a 100s production of the H$$^{-}$$ ion beam has been demonstrated with a beam current of 15 A by modifying the JT-60 negative ion source. At the higher current, the long pulse production of the negative ions has been tried by the mitigation of the arcing in the plasma inside the ion source. As for the long pulse acceleration of the negative ions in the MAMuG accelerator, the beam steering angle has been controlled to reduce the power loading of the acceleration grids A pulse duration time has been significantly extended from 0.4 s to 60 s at reasonable beam power for ITER requirement. The achieved pulse duration time is limited by the capacity of the power supplies in the test stand. In the range of $$<$$ 60 s, there are no degradations of beam optics and voltage holding capability in the accelerator. It leads to the further extension of the pulse duration time at higher power density. This paper reports the latest results of development on the negative ion source and accelerator at JAEA.

Journal Articles

22A beam production of the uniform negative ions in the JT-60 negative ion source

Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Grisham, L. R.*; Hatayama, Akiyoshi*; Shibata, Takanori*; Yamamoto, Takashi*; Akino, Noboru; Endo, Yasuei; et al.

Fusion Engineering and Design, 96-97, p.616 - 619, 2015/10

 Times Cited Count:10 Percentile:68(Nuclear Science & Technology)

In JT-60 Super Advanced for the fusion experiment, 22A, 100s negative ions are designed to be extracted from the world largest ion extraction area of 450 mm $$times$$ 1100 mm. One of the key issues for producing such as high current beams is to improve non-uniform production of the negative ions. In order to improve the uniformity of the negative ions, a tent-shaped magnetic filter has newly been developed and tested for JT-60SA negative ion source. The original tent-shaped filter significantly improved the logitudunal uniformity of the extracted H$$^{-}$$ ion beams. The logitudinal uniform areas within a $$pm$$10 deviation of the beam intensity were improved from 45% to 70% of the ion extraction area. However, this improvement degrades a horizontal uniformity. For this, the uniform areas was no more than 55% of the total ion extraction area. In order to improve the horizontal uniformity, the filter strength has been reduced from 660 Gasus$$cdot$$cm to 400 Gasus$$cdot$$cm. This reduction improved the horizontal uniform area from 75% to 90% without degrading the logitudinal uniformity. This resulted in the improvement of the uniform area from 45% of the total ion extraction areas. This improvement of the uniform area leads to the production of a 22A H$$^{-}$$ ion beam from 450 mm $$times$$ 1100 mm with a small amount increase of electron current of 10%. The obtained beam current fulfills the requirement for JT-60SA.

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:35 Percentile:87.83(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 production of high current negative ion beam by using actively temperature controlled plasma grid for JT-60SA negative ion source

Kojima, Atsushi; Hanada, Masaya; Yoshida, Masafumi; Umeda, Naotaka; Hiratsuka, Junichi; Kashiwagi, Mieko; Tobari, Hiroyuki; Watanabe, Kazuhiro; Grisham, L. R.*; NB Heating Technology Group

AIP Conference Proceedings 1655, p.060002_1 - 060002_10, 2015/04

 Times Cited Count:6 Percentile:88.59

In this paper, the recent activities on the new test stand are reported toward demonstration of the long pulse production for 22A, 100s negative ion beams. As for the temperature control of the plasma grid, a prototype of the grid with cooling/heating by circulating a high-temperature fluorinated fluid has been improved to cover the full extraction area by using 5 segments of the PG. These grids were found to have a capability to control the temperature with a time constant of 10s as well as the prototype grid. As a result, 15A negative ion beams for 100s have been achieved.

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

Non-linear dependence of deflection angle on beam steering control grid displacement in accelerator for N-NBI

Hiratsuka, Junichi; Hanada, Masaya; Umeda, Naotaka; Kojima, Atsushi; Kashiwagi, Mieko; Watanabe, Kazuhiro; Tobari, Hiroyuki; Yoshida, Masafumi

Plasma and Fusion Research (Internet), 10(Sp.2), p.3405045_1 - 3405045_4, 2015/04

To produce high current density ($$>$$ 200 A/m$$^{2}$$), high-energy ($$>$$ 1 MeV) negative ion beams for long pulse duration time (1 hour) for International Thermo-nuclear Experimental Reactor (ITER), the suppression of the direct interception of the negative ions with the grids has been carefully investigated with studying the deflection angle by aperture displacement technique. The non-linear dependence of the deflection angle appears at the aperture diameter of $$>$$ 14 mm on a steering control grid (SCG). From this dependence, the aperture diameter and the offset distance of the SCG has been designed to be 16 mm and 0.7 mm, respectively and tested in a prototype accelerator for ITER. Each of the beamlets on the multiple apertures is properly steered with compensation of the deflection due to the residual magnetic field in the accelerator and the grid power loading was significantly reduced. It resulted in a 10% enhancement of the accelerated beam current.

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.

JAEA Reports

Development of the control system with versatile PLCs for the long-pulse negative ion source

Komata, Masao; Shimizu, Tatsuo; Ozeki, Masahiro; Kojima, Atsushi; Hanada, Masaya

JAEA-Technology 2014-041, 50 Pages, 2015/01


In JT-60 Super Advanced, the machine for nuclear fusion research with superconducting magnets for long pulse operation, the negative-ion-base neutral beam injector is required to extend the pulse duration time 10 s to 100 s. In order to realize the long-pulse N-NB injector, the control system of the power supplies for the negative ion source has been newly developed. The control system with use of the versatile devices such as PLC was designed for an ease extension of the functions. Since the control system should have the many different functions which require the wide range of the sampling time of 1 milli-second to 10, all of the functions are performed by distributing PLCs for each of the function. The developed control system has been applied in the tests of the JT-60 negative ion source, where a 100 s negative ion beam has been successfully produced. Through this test, the controllability of this system has been confirmed to be feasible for JT-60SA operation.

JAEA Reports

Measurement of pure water resistivity in a high temperature region

Yamanaka, Haruhiko; Maejima, Tetsuya; Terunuma, Yuto; Watanabe, Kazuhiro; Kashiwagi, Mieko; Hanada, Masaya

JAEA-Technology 2014-037, 12 Pages, 2014/12


Resistivity of a high temperature pure water has been measured up to 180$$^{circ}$$C which is the maximum water temperature in the ITER Neutral Beam Injector. The resistivity of the pure water is decreased by increasing the water temperature. It was found that even different resistivity water of 9 M$$Omega$$cm and 5 M$$Omega$$cm showed almost the same resistivity at the higher temperature region of 100$$^{circ}$$C. The resistivity of 0.36 M$$Omega$$cm was measured at the temperature of 180$$^{circ}$$C. This resistivity agreed well to the calculated value for the theoretical pure water.

Journal Articles

Dismantlement of large fusion experimental device JT-60U

Ikeda, Yoshitaka; Okano, Fuminori; Sakasai, Akira; Hanada, Masaya; Akino, Noboru; Ichige, Hisashi; Kaminaga, Atsushi; Kiyono, Kimihiro; Kubo, Hirotaka; Kobayashi, Kazuhiro; et al.

Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(4), p.167 - 178, 2014/12

The JT-60U torus was disassembled so as to newly install the superconducting tokamak JT-60SA torus. The JT-60U used the deuterium for 18 years, so the disassembly project of the JT-60U was the first disassembly experience of a fusion device with radioactivation in Japan. All disassembly components were stored with recording the data such as dose rate, weight and kind of material, so as to apply the clearance level regulation in future. The lessons learned from the disassembly project indicated that the cutting technologies and storage management of disassembly components were the key factors to conduct the disassembly project in an efficient way. After completing the disassembly project, efforts have been made to analyze the data for characterizing disassembly activities, so as to contribute the estimation of manpower needs and the radioactivation of the disassembly components on other fusion devices.

Journal Articles

Development and application of large bore ceramic ring for DC 1MV vacuum insulation

Tobari, Hiroyuki; Hanada, Masaya; Matsuyama, Hisayoshi*; Morikawa, Kazufumi*

Seramikkusu, 49(12), p.1050 - 1055, 2014/12

In ITER neutral beam injector, a large bore ceramic ring (1.56 m in outer diameter, 50 mm in thickness) for HV bushing has been required, which acts as an insulating feedthrough from gas-insulated transmission line of 1 MV power supply to beam source in vacuum. However, maximum outer diameter was limited less than 1 m in an early phase of development. Development of manufacturing technology of large bore ceramic ring up to $$phi$$1.56 m was a critical issue for ITER HV bushing. In this paper, R&Ds on large bore ceramic ring; a development of new forming method of such a large ring, optimization of sintering method and verification test of high-voltage holding capability toward ITER HV bushing in JAEA are presented.

Journal Articles

Disassembly of JT-60 tokamak device

Okano, Fuminori; Ikeda, Yoshitaka; Sakasai, Akira; Hanada, Masaya

Dai-27-Kai Genshiryoku Shisetsu Dekomisshoningu Gijutsu Koza Tekisuto, p.73 - 102, 2014/10

The disassembly of JT-60 tokamak device and its peripheral equipments, where the total weight was about 5400 tons, started in 2009 and accomplished in October 2012. This disassembly was required process for JT-60SA project, which is the Satellite Tokamak project under Japan-EU international corroboration to modify the JT-60 to the superconducting tokamak. This work was the first experience of disassembling a large radioactive fusion device based on Radiation Hazard Prevention Act in Japan. The cutting was one of the main problems in this disassembly, such as to cut the wielded parts together with toroidal field coils, and to cut the vacuum vessel into two. After solving these problems, the disassembly completed without disaster and accident.

Journal Articles

Safe disassembly and storage of radioactive components of JT-60U torus

Ikeda, Yoshitaka; Okano, Fuminori; Hanada, Masaya; Sakasai, Akira; Kubo, Hirotaka; Akino, Noboru; Chiba, Shinichi; Ichige, Hisashi; Kaminaga, Atsushi; Kiyono, Kimihiro; et al.

Fusion Engineering and Design, 89(9-10), p.2018 - 2023, 2014/10

 Times Cited Count:2 Percentile:17.55(Nuclear Science & Technology)

Disassembly of the JT-60U torus was started in 2009 after 18-years D$$_{2}$$ operations, and was completed in October 2012. The JT-60U torus was featured by the complicated and welded structure against the strong electromagnetic force, and by the radioactivation due to D-D reactions. Since this work is the first experience of disassembling a large radioactive fusion device in Japan, careful disassembly activities have been made. About 13,000 components cut into pieces with measuring the dose rates were removed from the torus hall and stored safely in storage facilities by using a total wokers of 41,000 person-days during 3 years. The total weight of the disassembly components reached up to 5,400 tons. Most of the disassembly components will be treated as non-radioactive ones after the clearance verification under the Japanese regulation in future. The assembly of JT-60SA has started in January 2013 after this disassembly of JT-60U torus.

Journal Articles

Disassembly of JT-60 tokamak device for JT-60SA Project; Disassembly of radioactivated large structures

Okano, Fuminori; Ikeda, Yoshitaka; Sakasai, Akira; Hanada, Masaya; JT-60 Team

Purazuma, Kaku Yugo Gakkai-Shi, 90(10), p.630 - 639, 2014/10

JT-60 tokamak device, as a largest nuclear fusion device in the world, started the experiments since 1985 and had accomplished the research and development of plasma performance toward the DEMO. The project has successfully completed it operation in August 2008 with many results such as accomplishment of break-even plasma condition in 1996. This disassembly was required for JT-60SA project, which is the Satellite Tokamak project under Japan-EU international corroboration to modify the JT-60 to the superconducting tokamak. This work was the first experience of disassembling a large radioactive fusion device based on Radiation Hazard Prevention Act in Japan. This report presents the outline of disassembly of JT-60 tokamak device.

Journal Articles

Disassembly of JT-60 tokamak device

Okano, Fuminori; Ikeda, Yoshitaka; Sakasai, Akira; Hanada, Masaya; JT-60 Team

NIFS-MEMO-67, p.344 - 352, 2014/02

no abstracts in English

Journal Articles

100s extraction of negative ion beams by using actively temperature-controlled plasma grid

Kojima, Atsushi; Hanada, Masaya; Yoshida, Masafumi; Tobari, Hiroyuki; Kashiwagi, Mieko; Umeda, Naotaka; Watanabe, Kazuhiro; Grisham, L. R.*

Review of Scientific Instruments, 85(2), p.02B312_1 - 02B312_5, 2014/02

 Times Cited Count:11 Percentile:48.3(Instruments & Instrumentation)

The negative ion source for JT-60SA is designed to produce high power and long pulse beams with a beam energy of 500 keV, a negative ion current of 22A and a pulse duration of 100s. One of the key issues toward long pulse production of such high-current beams is the control of the surface temperature on the plasma grid (PG) where cesium is layered. In order to optimize cesium layer on PG for long pulse duration, we have developed an actively cooled PG where fluorinated fluids having high boiling point of 270$$^{circ}$$C is circulated. While the surface temperature of the PG in the JT-60 negative ion source has been kept at 170$$^{circ}$$C for 100s with ramp-up time of 7s, stable long pulse beam extractions of 100s have been obtained. This current density is 90% of the required current density for JT-60 SA. The further increase of the current density is expected by optimizing the arc discharge power.

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