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Journal Articles

Direct energy conversion using Ni/SiC Schottky junction in $$^{237}$$Np and $$^{241}$$Am gamma ray regions

Fukuda, Tatsuo; Kobata, Masaaki; Shobu, Takahisa; Yoshii, Kenji; Kamiya, Junichiro; Iwamoto, Yosuke; Makino, Takahiro*; Yamazaki, Yuichi*; Oshima, Takeshi*; Shirai, Yasuhiro*; et al.

Journal of Applied Physics, 132(24), p.245102_1 - 245102_8, 2022/12

 Times Cited Count:0

Direct energy conversion has been investigated using Ni/SiC Schottky junctions with the irradiation of monochromatized synchrotron X-rays simulating the gamma rays of $$^{237}$$Np (30 keV) and $$^{241}$$Am (60 keV). From current-voltage measurements, electrical energies were obtained for both kinds of gamma rays. The energy conversion efficiencies were found to reach up to $$sim$$1.6%, which is comparable to those of a few other semiconducting systems reported thus far. This result shows a possibility of energy recovery from nuclear wastes using the present system, judging from the radiation tolerant nature of SiC. Also, we found different conversion efficiencies between the two samples. This could be understandable from hard X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements, suggesting the formation of Ni-Si compounds at the interface in the sample with a poor performance. Hence, such combined measurements are useful to provide information that cannot be obtained by electrical measurements alone.

Journal Articles

Progress of ITER full tungsten divertor technology qualification in Japan

Ezato, Koichiro; Suzuki, Satoshi; Seki, Yohji; Mori, Kensuke; Yokoyama, Kenji; Escourbiac, F.*; Hirai, Takeshi*; Kuznetsov, V.*

Fusion Engineering and Design, 98-99, p.1281 - 1284, 2015/10

 Times Cited Count:33 Percentile:95.37(Nuclear Science & Technology)

Japan Atomic Energy Agency (JAEA) is now devoting to development of Full-W ITER divertor outer vertical target (OVT), especially, PFU that needs to withstand the repetitive heat load as high as 20MW/m$$^{2}$$. JAEA have succeeded in demonstrating that the soundness of a bonding technology is sufficient for the full-W ITER divertor. For the development of bonding technology, the load carrying capability test on the W monoblock with a leg attachment to an OVT support structure was carried out and shows that the attachment can withstand against the uniaxial load more than 20 kN which is three times higher than the IO requirement. JAEA manufactured 6 small-scale mock-ups and tested under the repetitive heat load of 10 and 20 MW/m$$^{2}$$ to examine the durability of the divertor structure including W tile bonding and the cooling tube. All of the mock-ups could survived 5000 cycles at 10 MW/m$$^{2}$$ and 1000 cycles 20 MW/m$$^{2}$$ with no failure such as debonding of the W tile and water leak from the cooling tube. The number of cycles at 20 MW/m$$^{2}$$ is three times longer than the requirement of ITER divertor.

Journal Articles

Development of tungsten monoblock technology for ITER full-tungsten divertor in Japan

Seki, Yohji; Ezato, Koichiro; Suzuki, Satoshi; Yokoyama, Kenji; Mori, Kensuke; Hirai, Takeshi*; Escourbiac, F.*; Kuznetsov, V.*

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

Journal Articles

Measured and simulated transport of 1.9 MeV laser-accelerated proton bunches through an integrated test beam line at 1 Hz

Nishiuchi, Mamiko; Sakaki, Hironao; Hori, Toshihiko; Bolton, P.; Ogura, Koichi; Sagisaka, Akito; Yogo, Akifumi; Mori, Michiaki; Orimo, Satoshi; Pirozhkov, A. S.; et al.

Physical Review Special Topics; Accelerators and Beams, 13(7), p.071304_1 - 071304_7, 2010/07

 Times Cited Count:25 Percentile:80.5(Physics, Nuclear)

A laser-driven repetition-rated 1.9 MeV proton beam line composed of permanent quadrupole magnets (PMQs), a radio frequency (rf) phase rotation cavity, and a tunable monochromator is developed to evaluate and to test the simulation of laser-accelerated proton beam transport through an integrated system for the first time. In addition, the proton spectral modulation and focusing behavior of the rf phase rotationcavity device is monitored with input from a PMQ triplet. In the 1.9 MeV region we observe very weakproton defocusing by the phase rotation cavity. The final transmitted bunch duration and transverse profile are well predicted by the PARMILA particle transport code. The transmitted proton beam duration of 6 ns corresponds to an energy spread near 5% for which the transport efficiency is simulated to be 10%. The predictive capability of PARMILA suggests that it can be useful in the design of future higher energy transport beam lines as part of an integrated laser-driven ion accelerator system.

Journal Articles

Laser-driven proton accelerator for medical application

Nishiuchi, Mamiko; Sakaki, Hironao; Hori, Toshihiko; Bolton, P.; Ogura, Koichi; Sagisaka, Akito; Yogo, Akifumi; Mori, Michiaki; Orimo, Satoshi; Pirozhkov, A. S.; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.88 - 90, 2010/05

The concept of a compact ion particle accelerator has become attractive in view of recent progress in laser-driven ion acceleration. We report here the recent progress in the laser-driven proton beam transport at the Photo Medical Research Center (PMRC) at JAEA, which is established to address the challenge of laser-driven ion accelerator development for ion beam cancer therapy.

Journal Articles

Quantitative aspects of heterogeneity in soil organic matter dynamics in a cool-temperate Japanese beech forest; A Radiocarbon-based approach

Koarashi, Jun; Atarashi-Andoh, Mariko; Ishizuka, Shigehiro*; Miura, Satoru*; Saito, Takeshi*; Hirai, Keizo*

Global Change Biology, 15(3), p.631 - 642, 2009/03

 Times Cited Count:38 Percentile:73.07(Biodiversity Conservation)

Although it is well documented the possibility that global warming can lead to an acceleration of microbial decomposition of soil organic carbon (SOC), the magnitude and timing of this effect remains highly uncertain. The main reason is a lack of quantitative aspect of the heterogeneity in SOC biodegradability. To quantify the heterogeneity, we collected the soil and litter samples within a cool-temperate deciduous forest in Japan, separated chemically the samples into SOC fractions, determined their mean residence times (MRTs) based on the radiocarbon ($$^{14}$$C) measurements, and finally represented the soil as a complex of six SOC pools with different range of MRTs. Predicted response of the SOC pools to warming demonstrates that the rate of SOC loss from the fast-cycling SOC pool diminishes quickly because of the substrate availability; in contrast, the warming continues to accelerate SOC loss from slow-cycling pools with MRTs of 20-200 year over the next century.

Journal Articles

Evaluation of carbon cycle in forest by using radiocarbon as a tracer

Atarashi-Andoh, Mariko; Koarashi, Jun; Ishizuka, Shigehiro*; Saito, Takeshi*; Hirai, Keizo*

JAEA-Conf 2008-003, p.75 - 78, 2008/04

C-14 is an effective tracer in investigating the carbon dynamics in the environment. In this study, the measurements of C-14 in soil organic matter (SOM) in a deciduous forest were used to determine the turnover time and CO$$_{2}$$ production rate from SOM. In addition, monthly measurements of carbon isotopic ratios in soil-respired CO$$_{2}$$ and atmospheric CO$$_{2}$$ were conducted to characterize the seasonal variation of the contribution of each CO$$_{2}$$ source, such as SOM decomposition and root respiration.

Journal Articles

Radiocarbon-based estimation of soil carbon turnover in a cool-temperate beech forest

Koarashi, Jun; Atarashi-Andoh, Mariko; Ishizuka, Shigehiro*; Saito, Takeshi*; Hirai, Keizo*; Miura, Satoru*

Proceedings of International Symposium on Application of a Closed Experimental System to Modeling of $$^{14}$$C Transfer in the Environment, p.72 - 76, 2008/00

Recent debate has emphasized that our capacity to predict the response of soil organic carbon (SOC) to climate change depends on a clear understanding of the heterogeneity in SOC biodegradability. We collected soil samples from the Appi forest meteorology research site dominated by Japanese beech, separated the soil samples into three SOC fractions with a chemical method, and determined their radiocarbon isotope ratios using an accelerator mass spectrometry. The radiocarbon signatures allow us to estimate their turnover times (TTs), quantifying the rates of SOC decomposition. According to the estimated TTs, the SOC was distinguished into six SOC pools with distinct TTs of several years to $$>$$ 1000 years. The annual SOC decomposition rate was summed up to 0.47 kgC m$$^{-2}$$ y$$^{-1}$$, about a half of which was from the fastest-cycling pool (litter). Approximately 5% of SOC gave the over-millennium TTs, suggesting that this pool plays a role of a long-term carbon sequestration in the carbon cycle.

Journal Articles

High quality laser-produced proton beam generation by phase rotation

Noda, Akira*; Nakamura, Shu*; Iwashita, Yoshihisa*; Shirai, Toshiyuki*; Tongu, Hiromu*; Soda, Hikaru*; Daido, Hiroyuki; Mori, Michiaki; Kado, Masataka; Sagisaka, Akito; et al.

International Journal of Modern Physics B, 21(3&4), p.319 - 330, 2007/02

Laser ion production has been studied for downsizing of the accelerator dedicated for cancer therapy. For optimization of various parameters such as pre-pulse condition, target position, laser spot size on target, laser pulse width and so on, time of flight (TOF) measurement utilizing the detected signal by a plastic scintillation counter played an essential role for real time measurement. Protons up to 900 keV and 600 keV are produced from the thin foil targets of Ti 3 micron and 5 micron in thickness, respectively. Modification of the energy distribution of the laser-produced ions with Maxwell distribution by utilizing an RF electric field synchronized to the pulse laser, which is the rotation of the ion beam in the longitudinal phase space (phase rotation), has been demonstrated for the first time.

Journal Articles

ITER relevant high heat flux testing on plasma facing surfaces

Hirai, Takeshi*; Ezato, Koichiro; Majerus, P.*

Materials Transactions, 46(3), p.412 - 424, 2005/03

 Times Cited Count:108 Percentile:90.1(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Properties of internal transport barrier formation in JT-60U

Sakamoto, Yoshiteru; Suzuki, Takahiro; Ide, Shunsuke; Koide, Yoshihiko; Takenaga, Hidenobu; Kamada, Yutaka; Fujita, Takaaki; Fukuda, Takeshi; Takizuka, Tomonori; Shirai, Hiroshi; et al.

Nuclear Fusion, 44(8), p.876 - 882, 2004/08

 Times Cited Count:30 Percentile:68.09(Physics, Fluids & Plasmas)

Response of the ion thermal diffusivity to the radial electric field Er shear has been investigated in JT-60U and the following results were found. (1) In the case of positive magnetic shear (PS) plasma, the ion thermal diffusivity in the core region shows L mode state, weak internal transport barrier (ITB), and strong ITB depending upon the heating power. In the case of reversed magnetic shear (RS) plasma, however, no power degradation of the ion thermal diffusivity is observed. (2) In the case of weak ITB, the ion thermal diffusivity decreases gradually with increasing the Er shear for both PS and RS plasmas. There exists a threshold of an effective Er shear to change its state from weak to strong ITBs. (3) The threshold of the effective Er shear in the case of RS plasma is small compared with that in the case of PS plasma.

Journal Articles

Energetic protons from a few-micron metallic foil evaporated by an intense laser pulse

Matsukado, Koji*; Esirkepov, T. Z.; Kinoshita, Kenichi*; Daido, Hiroyuki; Utsumi, Takayuki*; Li, Z.*; Fukumi, Atsushi*; Hayashi, Yukio; Orimo, Satoshi; Nishiuchi, Mamiko; et al.

Physical Review Letters, 91(21), p.215001_1 - 215001_4, 2003/11

 Times Cited Count:135 Percentile:95.39(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Stiff temperature profiles in JT-60U ELMy H-mode plasmas

Mikkelsen, D. R.*; Shirai, Hiroshi; Urano, Hajime*; Takizuka, Tomonori; Kamada, Yutaka; Hatae, Takaki; Koide, Yoshihiko; Asakura, Nobuyuki; Fujita, Takaaki; Fukuda, Takeshi*; et al.

Nuclear Fusion, 43(1), p.30 - 39, 2003/01

 Times Cited Count:27 Percentile:63.71(Physics, Fluids & Plasmas)

The stiffness of thermal transport in ELMy H-modes is explained in a series of carefully chosen JT-60U plasmas, and measured temperature are compared with the predictions of several transport models. A heating power scan with constant Tped, a scan of pedestal temperature Tped with constant heating power, and an on/off-axis heating comparison are presented. Predictions of the RLWB and IFS/PPPL models generally agree with the measured temperature outside $$r$$$$sim$$0.3$$a$$, but the Multimode model uniformly predicts temperatures that are too high except in the central region.

Journal Articles

Fusion plasma performance and confinement studies on JT-60 and JT-60U

Kamada, Yutaka; Fujita, Takaaki; Ishida, Shinichi; Kikuchi, Mitsuru; Ide, Shunsuke; Takizuka, Tomonori; Shirai, Hiroshi; Koide, Yoshihiko; Fukuda, Takeshi; Hosogane, Nobuyuki; et al.

Fusion Science and Technology (JT-60 Special Issue), 42(2-3), p.185 - 254, 2002/09

 Times Cited Count:32 Percentile:48.48(Nuclear Science & Technology)

With the main aim of providing physics basis for ITER and the steady-state tokamak reactors, JT-60/JT-60U has been developing and optimizing the operational concepts, and extending the discharge regimes toward sustainment of high integrated performance in the reactor relevant parameter regime. In addition to achievement of the equivalent break-even condition (QDTeq up to 1.25) and a high fusion triple product = 1.5E21 m-3skeV, JT-60U has demonstrated the integrated performance of high confinement, high beta-N, full non-inductive current drive with a large fraction of bootstrap current in the reversed magnetic shear and in the high-beta-p ELMy H mode plasmas characterized by both internal and edge transport barriers. The key factors in optimizing these plasmas are profile and shape controls. As represented by discovery of various Internal Transport Barriers, JT-60/JT-60U has been emphasizing freedom and restriction of profiles in various confinement modes. JT-60U has demonstrated applicability of these high confinement modes to ITER and also clarified remaining issues.

Journal Articles

Power dependence of ion thermal diffusivity at the internal transport barrier in JT-60U

Sakamoto, Yoshiteru; Suzuki, Takahiro; Ide, Shunsuke; Koide, Yoshihiko; Takenaga, Hidenobu; Kamada, Yutaka; Fujita, Takaaki; Takizuka, Tomonori; Shirai, Hiroshi; Fukuda, Takeshi

Purazuma, Kaku Yugo Gakkai-Shi, 78(9), p.941 - 948, 2002/09

no abstracts in English

Journal Articles

Formation and sustainment of ITBs under various heating schemes in JT-60U

Ide, Shunsuke; Suzuki, Takahiro; Sakamoto, Yoshiteru; Takenaga, Hidenobu; Koide, Yoshihiko; Fujita, Takaaki; Fukuda, Takeshi; Kamada, Yutaka; Shirai, Hiroshi; Takizuka, Tomonori

Plasma Physics and Controlled Fusion, 44(5A), p.A137 - A142, 2002/05

 Times Cited Count:17 Percentile:49.71(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Energy confinement scaling for reversed-shear plasmas with internal transport barrier in JT-60U

Takizuka, Tomonori; Sakamoto, Yoshiteru; Fukuda, Takeshi; Fujita, Takaaki; Kamada, Yutaka; Suzuki, Takahiro; Ide, Shunsuke; Shirai, Hiroshi

Plasma Physics and Controlled Fusion, 44(5A), p.A423 - A428, 2002/05

 Times Cited Count:13 Percentile:41.26(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Edge-core relationship of ELMy H-mode plasmas in JT-60U

Urano, Hajime*; Kamada, Yutaka; Shirai, Hiroshi; Takizuka, Tomonori; Kubo, Hirotaka; Takenaga, Hidenobu; Miura, Yukitoshi; Hatae, Takaki; Fukuda, Takeshi

Plasma Physics and Controlled Fusion, 44(5A), p.A437 - A443, 2002/05

 Times Cited Count:18 Percentile:51.66(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Thermal energy confinement properties of ELMy H mode plasmas in JT-60U

Urano, Hajime; Kamada, Yutaka; Shirai, Hiroshi; Takizuka, Tomonori; Ide, Shunsuke; Fujita, Takaaki; Fukuda, Takeshi

Nuclear Fusion, 42(1), p.76 - 85, 2002/01

 Times Cited Count:32 Percentile:70.06(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Thermal energy confinement of high-triangularity ELMy H-mode plasmas in JT-60U

Urano, Hajime*; Kamada, Yutaka; Shirai, Hiroshi; Takizuka, Tomonori; Kubo, Hirotaka; Hatae, Takaki; Fukuda, Takeshi

Plasma Physics and Controlled Fusion, 44(1), p.11 - 21, 2002/01

 Times Cited Count:22 Percentile:57.96(Physics, Fluids & Plasmas)

no abstracts in English

64 (Records 1-20 displayed on this page)