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988 results on '"Okuno, K."'

4. Operation-induced degradation mechanisms of 275-nm-band AlGaN-based deep-ultraviolet light-emitting diodes fabricated on a sapphire substrate.

Author

Chichibu, S. F., Nagata, K., Oya, M., Kasuya, T., Okuno, K., Ishiguro, H., Saito, Y., Takeuchi, T., and Shima, K.

Subjects
LIGHT emitting diodes, POSITRON annihilation, SAPPHIRES, QUANTUM wells, QUANTUM efficiency, ENERGY bands, GOLD clusters
Abstract

Degradation mechanisms of 275-nm-band AlxGa1-xN multiple quantum well deep-ultraviolet light-emitting diodes fabricated on a (0001) sapphire substrate were investigated under hard operation conditions with the current of 350 mA and the junction temperature of 105 °C. The optical output power (Po) initially decreased by about 20% within the operating time less than 102 h and then gradually decreased to about 60% by 484 h. For elucidating the causes for the initial and subsequent degradations, complementary electrical, time-resolved photoluminescence (TRPL), and impurity characterizations were carried out making a connection with the energy band profiles. Because the degradation of the wells was less significant than the Po reduction, the initial degradation is attributed essentially to the decrease in carrier injection efficiency ( η injection ), not in internal quantum efficiency of the wells, most likely due to depassivation of initially H-passivated preexisting nonradiative recombination centers (NRCs) in a Mg-doped p-type Al0.85Ga0.15N electron blocking layer. The principal cause for the subsequent Po reduction until 484 h is attributed to further decrease in η injection due to the appearance of certain current bypasses in addition to continuous depassivation of the NRCs in p-type AlxGa1-xN layers. According to our database on the species of vacancy-type defects acting as NRCs in GaN and AlN, which have been identified using the combination of positron annihilation and TRPL measurements, vacancy clusters comprised of a cation vacancy (VIII) and nitrogen vacancies (VN), such as V III V N 2 ∼ 4 , are the most suspicious origins of the NRCs in Mg-doped p-type AlxGa1-xN layers. [ABSTRACT FROM AUTHOR]

Published
2023
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20. Microstructural observation of ITER [Nb.sub.3]Sn strands under bending strain

Author

Banno, N., Takeuchi, T., Koizumi, N., and Okuno, K.

Subjects
Bending -- Analysis, Niobium -- Magnetic properties, Niobium -- Electric properties, Niobium -- Mechanical properties, Nuclear reactors -- Design and construction, Superconducting magnets -- Mechanical properties, Technical institutes -- Management, Tin alloys -- Magnetic properties, Tin alloys -- Electric properties, Tin alloys -- Mechanical properties, Company business management, Business, Electronics, Electronics and electrical industries, International Thermonuclear Experimental Reactor -- Management
Published
2010

21. Superconducting property and strain effect study of the [Nb.sub.3]Sn strands developed for ITER

Author

Nunoya, Y., Hemmi, T., Nabara, Y., Matsui, K., Isono, T., Takahashi, Y., Koizumi, N., and Okuno, K.

Subjects
Niobium -- Magnetic properties, Niobium -- Electric properties, Nuclear reactors -- Design and construction, Technical institutes -- Management, Tin alloys -- Magnetic properties, Tin alloys -- Electric properties, Company business management, Business, Electronics, Electronics and electrical industries, International Thermonuclear Experimental Reactor -- Management
Published
2010

22. Development of the ITER toroidal field coil winding pack in Japan

Author

Koizumi, N., Nakajima, H., Matsui, K., Hemmi, T., Takano, K., Okuno, K., Hasegawa, M., Kakui, H., and Senda, I.

Subjects
Nuclear reactors -- Design and construction, Superconducting magnets -- Design and construction, Winding machines -- Design and construction, Welding research, Business, Electronics, Electronics and electrical industries
Published
2010

23. Status report on the toroidal field coils for the ITER project

Author

Savary, F., Bonito-Oliva, A., Gallix, R., Knaster, J., Koizumi, N., Mitchell, N., Nakajima, H., Okuno, K., and Sborchia, C.

Subjects
Electric coils -- Testing, Niobium -- Magnetic properties, Niobium -- Electric properties, Nuclear reactors -- Design and construction, Superconducting magnets -- Design and construction, Technical institutes -- Research, Tin alloys -- Magnetic properties, Tin alloys -- Electric properties, Business, Electronics, Electronics and electrical industries, International Thermonuclear Experimental Reactor -- Research
Published
2010

27. Characterization of [Nb.sub.3]Al strands subjected to an axial-strain for a fusion DEMO reactor

Author

Hemmi, T., Koizumi, N., Nunoya, Y., Okui, Y., Matsui, K., Nabara, Y., Isono, T., Takahashi, Y., Okuno, K., Banno, N., Kikuchi, A., Iijima, Y., and Takeuchi, T.

Subjects
Aluminum alloys -- Electric properties, Aluminum alloys -- Mechanical properties, Fusion reactors -- Design and construction, Niobium alloys -- Electric properties, Niobium alloys -- Mechanical properties, Tin alloys -- Electric properties, Tin alloys -- Mechanical properties, Business, Electronics, Electronics and electrical industries
Published
2009

28. Test results from the PF conductor insert coil and implications for the ITER PF system

Author

Bessette, D., Bottura, L., Devred, A., Mitchell, N., Okuno, K., Nunoya, Y., Sborchia, C., Takahashi, Y., Verweij, A., Vostner, A., Zanino, R., and Zapretilina, E.

Subjects
Electrical conduits -- Design and construction, Niobium alloys -- Thermal properties, Niobium alloys -- Magnetic properties, Nuclear reactors -- Design and construction, Titanium -- Magnetic properties, Titanium -- Thermal properties, Business, Electronics, Electronics and electrical industries
Published
2009

29. Installation and test programme of the ITER poloidal field conductor insert (PFCI) in the ITER test facility at JAEA Naka

Author

Nunoya, Y., Takahashi, Y., Hamada, K., Isono, T., Matsui, K., Oshikiri, M., Nabara, Y., Hemmi, T., Nakajima, H., Kawano, K., Tsutsumi, F., Takano, K., Uno, Y., Koizumi, N., Okuno, K., Baker, W., Salpietro, E., Rajainmaki, H., Sborchia, C., and Mitchell, N.

Subjects
Electrical conduits -- Design and construction, Electrical conduits -- Heating, cooling and ventilation, Niobium alloys -- Magnetic properties, Niobium alloys -- Electric properties, Nuclear reactors -- Design and construction, Nuclear reactors -- Testing, Titanium -- Magnetic properties, Titanium -- Electric properties, Business, Electronics, Electronics and electrical industries
Published
2009

30. Test results of the third Japanese SULTAN sample

Author

Matsui, K., Isono, T., Nunoya, Y., Hemmi, T., Okui, Y., Oshikiri, M., Koizumi, N., Takahashi, Y., Okuno, K., Stepanov, B., and Bruzzone, P.

Subjects
Niobium alloys -- Magnetic properties, Niobium alloys -- Electric properties, Nuclear reactors -- Design and construction, Superconductive devices -- Design and construction, Tin alloys -- Magnetic properties, Tin alloys -- Electric properties, Business, Electronics, Electronics and electrical industries
Published
2009

33. Investigation of a mechanism forming irregular loops in large CIC conductor

Author

Yagai, T., Nara, Y., Ohmura, J., Tsuda, M., Hamajima, T., Nunoya, Y., Okuno, K., and Takahata, K.

Subjects
Electric currents -- Evaluation, Superconductors -- Evaluation, Business, Electronics, Electronics and electrical industries
Abstract

The mechanism of the coupling loss is examined by measuring the trajectories of strands of sample CIC conductor. The studies have shown that probable loop lengths of long conductors are calculated by contact probabilities of two strands at each contactable point of two sub cables by newly developed function of twisting pitches.

Published
2008

34. Results of R&D on ITER-TF winding critical issues

Author

Koizumi, N., Nakajima, H., Matsui, K., Isono, T., Okuno, K., Takayanagi, T., Kuno, K., and Senda, I.

Subjects
Magnetic fields -- Analysis, Niobium -- Magnetic properties, Niobium -- Thermal properties, Nuclear reactors -- Design and construction, Tin alloys -- Magnetic properties, Tin alloys -- Thermal properties, Business, Electronics, Electronics and electrical industries
Abstract

The tests and analysis performed in Japan Atomic Energy Agency (JAEA) to solve the major technical issues in manufacturing the Toroidal Field coil winding pack (TFWP) are discussed. New impregnation method is under development for shortening the impregnation period.

Published
2008

35. Results of a new generation of ITER TF conductor samples in SULTAN

Author

Bruzzone, P., Stepanov, B., Wesche, R., Salpietro, E., Vostner, A., Okuno, K., Isono, T., Takahashi, Y., Hyoung Chan Kim, Keeman Kim, Shikov, A.K., and Sytnikov, V.E.

Subjects
Niobium -- Magnetic properties, Niobium -- Electric properties, Nuclear reactors -- Design and construction, Superconductors -- Analysis, Tin alloys -- Magnetic properties, Tin alloys -- Electric properties, Business, Electronics, Electronics and electrical industries
Abstract

The test results of the new generation of ITER TF conductor samples in SULTAN are discussed. The homogenization of performance toward the upper range has provided an effective margin for the operation of the ITER coil system.

Published
2008

46. Predictive analysis of the ITER Poloidal Field Conductor Insert (PFCI) test program

Author

Zanino, R., Astrov, M., Bagnasco, M., Baker, W., Bellina, F., Ciazynski, D., Egorov, S., Kim, K., Kvitkovic, J.L., Lacroix, B., Martovetsky, N., Mitchell, N., Muzzi, L., Nunoya, Y., Okuno, K., Polak, M., Ribani, P.L., Salpietro, E., Richard, L. Savoldi, Sborchia, C., Takahashi, Y., Weng, P., Wesche, R., Zani, L., and Zapretilina, E.

Subjects
Superconducting magnets -- Electric properties, Fusion reactors -- Design and construction, Electric coils -- Electric properties, Electric coils -- Magnetic properties, Business, Electronics, Electronics and electrical industries
Abstract

The predictive analysis of the International Thermonuclear Experimental Reactor (ITER) Poloidal Field Conductor Insert (PFCI) test program is presented. PFCI is the first insert coil based on NbTi and is aimed at bridging the extrapolation gap between its full-size short sample and the ITER Poloidal Field (PF) coils.

Published
2007

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