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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:1 Percentile:7.86(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:7 Percentile:44.58(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:6 Percentile:39.69(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:59.78(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

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:90.95

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.

Journal Articles

Demonstration of in-situ relative calibration method for a Thomson scattering diagnostic on TST-2

Tojo, Hiroshi; Ejiri, Akira*; Hiratsuka, Junichi*; Yamaguchi, Takashi*; Takase, Yuichi*; Itami, Kiyoshi; Hatae, Takaki

Journal of Instrumentation (Internet), 7(4), p.P04005_1 - P04005_11, 2012/04

 Times Cited Count:3 Percentile:19.44(Instruments & Instrumentation)

Journal Articles

First measurement of electron temperature from signal ratios in a double-pass Thomson scattering system

Tojo, Hiroshi; Ejiri, Akira*; Hiratsuka, Junichi*; Yamaguchi, Takashi*; Takase, Yuichi*; Itami, Kiyoshi; Hatae, Takaki

Review of Scientific Instruments, 83(2), p.023507_1 - 023507_4, 2012/02

 Times Cited Count:10 Percentile:48.59(Instruments & Instrumentation)

Journal Articles

Successful BNCT for patients with cutaneous and mucosal melanomas; Report of 4 cases

Morita, Norimasa*; Hiratsuka, Junichi*; Kuwabara, Chiaki*; Aihara, Teruhito*; Ono, Koji*; Fukuda, Hiroshi*; Kumada, Hiroaki; Harada, Tamotsu*; Imajo, Yoshinari*

Proceedings of 12th International Congress on Neutron Capture Therapy (ICNCT-12), p.18 - 20, 2006/12

Since 2003, group of Kawasaki Medical School has conducted BNCT clinical trials on melanomas at the Kyoto University Research Reactor (KUR) and Japan Research Reactor No.4 (JRR-4). We report 4 patients given BNCT for malignant melanomas, 2 with superficial spreading types on the heel, 1 with mucosal melanoma in the nasal cavity, and 1with a melanoma on the vulva and in the vagina. Although 2 patients experienced normal-tissue damage that exceeded the tolerance level, all the participants were cured within a few months of treatment. BNCT was shown to be a promising treatment for mucosal, as well as for cutaneous, melanomas.

Journal Articles

Development of a real-time thermal neutron monitor and its clinical application

Ishikawa, Masayori*; Ono, Koji*; Matsumura, Akira*; Yamamoto, Tetsuya*; Hiratsuka, Junichi*; Miyatake, Shinichi*; Kato, Itsuro*; Sakurai, Yoshinori*; Kobayashi, Toru*; Kumada, Hiroaki; et al.

Proceedings of 12th International Congress on Neutron Capture Therapy (ICNCT-12), p.397 - 400, 2006/10

An ultraminiature thermal neutron monitor which was named SOF detector (Scintillator with Optical Fiber detector) had been developed for BNCT treatment. We had been experienced 15 clinical trials using SOF detector until the end of 2005, some measurements got good results, and some got unacceptable results. One reason of the unacceptable results was due to dislocation of the detector during treatment. This is because it is difficult to fix the SOF detector on patient's skin without strong sticker. To overcome this problem, a loop-type SOF probe was developed. By using the loop-type SOF detector, fixing on the patient's skin was much easier.

Journal Articles

Wall conditioning and experience of the carbon-based first wall in JT-60U

Masaki, Kei; Yagyu, Junichi; Arai, Takashi; Kaminaga, Atsushi; Kodama, Kozo; Miya, Naoyuki; Ando, Toshiro; Hiratsuka, Hajime; Saido, Masahiro

Fusion Science and Technology (JT-60 Special Issue), 42(2-3), p.386 - 395, 2002/09

 Times Cited Count:8 Percentile:49.76(Nuclear Science & Technology)

The wall conditioning of JT-60U consists of the 300$$^{circ}$$C baking, He-TDC, He-GDC, tokamak discharge cleaning and boronization. Using these methods, total pressure of the vacuum vessel reached finally 10$$^{-6}$$ $$sim$$ 10$$^{-5}$$ Pa. The oxygen impurity was decreased to $$sim$$0.5%. The experience with the carbon-based first wall showed that taper shaping is effective to reduce the local heat concentration to the tile edges. The observed poloidal asymmetric deposition of carbon on the divertor region implies that the carbon impurity produced in the outer divertor contributes to the deposition on the inner divertor. In 1992 and 1993, the B$$_{4}$$C converted CFC tiles were installed in the outer divertor to reduce chemical sputtering of CFC tiles and oxygen impurity. The reduction was successfully demonstrated with the B$$_{4}$$C converted CFC tiles. In order to understand the tritium behavior in JT-60U, tritium in the first wall and the exhaust gas were measured. The estimated tritium inventory in the first wall was $$sim$$50% of the generated tritium.

Journal Articles

Properties of thin boron coatings formed during deuterated-boronization in JT-60

Yagyu, Junichi; Ogiwara, Norio; Saido, Masahiro; Okabe, Tomokazu; Hiratsuka, Hajime; Miyo, Yasuhiko; Naramoto, Hiroshi; Yamamoto, Shunya; Takeshita, Hidefumi; Aoki, Yasushi; et al.

Journal of Nuclear Materials, 241-243, p.579 - 584, 1997/00

 Times Cited Count:15 Percentile:75.44(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Effects of plasma behavior on in-vessel components in JT-60 operation

Hiratsuka, Hajime; ; ; Arai, Takashi; Masaki, Kei; Neyatani, Yuzuru; Yagyu, Junichi; Kaminaga, Atsushi; Saido, Masahiro

Fusion Technology 1996, 0, 4 Pages, 1996/00

no abstracts in English

Journal Articles

Development and operation of first wall in JT-60U high-power heated discharges

Masaki, Kei; ; Arai, Takashi; Hiratsuka, Hajime; Yagyu, Junichi; Saido, Masahiro; Ogiwara, Norio; Higashijima, Satoru

16th IEEE/NPSS Symp. on Fusion Engineering (SOFE '95), p.638 - 641, 1995/00

no abstracts in English

Journal Articles

Initial boronization of JT-60U tokamak using decaborane

Saido, Masahiro; Ogiwara, Norio; Shimada, Michiya; Arai, Takashi; Hiratsuka, Hajime; ; Shimizu, Masatsugu; Ninomiya, Hiromasa; Nakamura, Hiroo; *; et al.

Japanese Journal of Applied Physics, 32(7), p.3276 - 3281, 1993/07

 Times Cited Count:54 Percentile:90.71(Physics, Applied)

no abstracts in English

Oral presentation

Demonstration of in-situ relative calibration method for a Thomson scattering diagnostic on TST-2

Tojo, Hiroshi; Ejiri, Akira*; Hiratsuka, Junichi*; Yamaguchi, Takashi*; Takase, Yuichi*; Itami, Kiyoshi

no journal, , 

Oral presentation

Development of Thomson scattering diagnostics in JT-60SA

Tojo, Hiroshi; Hatae, Takaki; Sakuma, Takeshi; Hamano, Takashi; Itami, Kiyoshi; Ejiri, Akira*; Hiratsuka, Junichi*; Yamaguchi, Takashi*; Takase, Yuichi*

no journal, , 

no abstracts in English

Oral presentation

Optimization of the magnetic configlation toward large current beam production in the JT-60SA negative ion source

Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Umeda, Naotaka; Hiratsuka, Junichi; Akino, Noboru; Endo, Yasuei; Komata, Masao; Mogaki, Kazuhiko; et al.

no journal, , 

One of the key issues for producing high current beams in JT-60SA is a uniform production of the negative ions over the large ion extraction area. Non-uniformity of the negative ion beams in the JT-60 negative ion source was improved by modifying the magnetic filter in the source from the PG filter to a tent-shaped filter. In this work, in order to clarify the influence of the magnetic filter modification on arc efficiency and co-electron current is investigated by means of measurements of H ion, H atoms, co-electron current and beam intensity. As a result, the arc efficiency increase due to increase of H ions and H atoms by reduction of filter field. Although the higher electrons current was extracted than the original PG filter, the co-extracted electron could be suppressed by optimization of the bias voltage. This result contributes to extend the pulse duration time up to 100 s for JT-60SA.

25 (Records 1-20 displayed on this page)