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290 results on '"Johzaki T"'

1. Fast electron beam guiding for effective core heating

Author

Johzaki T., Sunahara A., Fujioka S., Nagatomo H., Sakagami H., and Mima K.

Subjects
Physics, QC1-999
Abstract

In cone-guiding fast ignition, the guiding of fast electron beam with significantly large beam divergence is one of the most important issues for achieving efficient core heating. We proposed two guiding schemes; one is the “Tongari” tip guiding by resistive magnetic fields and the other is the guiding by externally applying axial magnetic fields. The guiding performances for these two schemes are demonstrated by Particle-In-Cell and Fokker-Planck simulations.

Published
2013
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2. Optimum design of imploded core plasma for effective fast ignition at GXII

Author

Nagatomo H., Johzaki T., Sunahara A., Sakagami H., Yanagawa T., and Mima K.

Subjects
Physics, QC1-999
Abstract

In the implosion phase of the fast ignition scheme, most critical issues are breakup of the cone tip and the formation of high ρ-R core plasma to improve its heating efficiency. For the integrated fast ignition experiment at ILE Osaka University, robust and reliable implosion must be redesign. In this paper, feasible target design under the constraint condition of existing GXII and LFEX facilities is studied using two-dimensional radiation hydrodynamic simulations, and an optimum target design based on low velocity implosion is proposed. The advantages of low velocity implosion are low adiabat, robust against Rayleigh-Taylor instability, which are verified. Also longer life time of compressed core plasma which is preferable for fast ignition is confirmed in this study.

Published
2013
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3. Suppression effects of Weibel instability for fast electron divergence

Author

Sakagami H., Johzaki T., Taguchi T., and Mima K.

Subjects
Physics, QC1-999
Abstract

Quasi-static magnetic fields, which are induced by the Weibel instability and grow to more than hundred Megagauss, lead to large divergence angle of fast electrons, hence lower energy coupling. To suppress the divergence, two different structures, namely density trough and punched out holes, are introduced to targets. In the density trough target, the Weibel instability is enhanced and the divergence is getting worse. On the other hand, the divergence angle is improved but the number of electrons is degraded for fast electrons (

Published
2013
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4. Implosion and heating experiments of fast ignition targets by Gekko-XII and LFEX lasers

Author

Shiraga H., Fujioka S., Nakai M., Watari T., Nakamura H., Arikawa Y., Hosoda H., Nagai T., Koga M., Kikuchi H., Ishii Y., Sogo T., Shigemori K., Nishimura H., Zhang Z., Tanabe M., Ohira S., Fujii Y., Namimoto T., Sakawa Y., Maegawa O., Ozaki T., Tanaka K.A., Habara H., Iwawaki T., Shimada K., Key M., Norreys P., Pasley J., Nagatomo H., Johzaki T., Sunahara A., Murakami M., Sakagami H., Taguchi T., Norimatsu T., Homma H., Fujimoto Y., Iwamoto A., Miyanaga N., Kawanaka J., Kanabe T., Jitsuno T., Nakata Y., Tsubakimoto K., Sueda K., Kodama R., Kondo K., Morio N., Matsuo S., Kawasaki T., Sawai K., Tsuji K., Murakami H., Sarukura N., Shimizu T., Mima K., and Azechi H.

Subjects
Physics, QC1-999
Abstract

The FIREX-1 project, the goal of which is to demonstrate fuel heating up to 5 keV by fast ignition scheme, has been carried out since 2003 including construction and tuning of LFEX laser and integrated experiments. Implosion and heating experiment of Fast Ignition targets have been performed since 2009 with Gekko-XII and LFEX lasers. A deuterated polystyrene shell target was imploded with the 0.53- μm Gekko-XII, and the 1.053- μm beam of the LFEX laser was injected through a gold cone attached to the shell to generate hot electrons to heat the imploded fuel plasma. Pulse contrast ratio of the LFEX beam was significantly improved. Also a variety of plasma diagnostic instruments were developed to be compatible with harsh environment of intense hard x-rays (γ rays) and electromagnetic pulses due to the intense LFEX beam on the target. Large background signals around the DD neutron signal in time-of-flight record of neutron detector were found to consist of neutrons via (γ,n) reactions and scattered gamma rays. Enhanced neutron yield was confirmed by carefully eliminating such backgrounds. Neutron enhancement up to 3.5 × 107 was observed. Heating efficiency was estimated to be 10–20% assuming a uniform temperature rise model.

Published
2013
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5. Effects of laser temporal profile on fast electron characteristics

Author

Hata M., Sakagami H., Johzaki T., and Nagatomo H.

Subjects
Physics, QC1-999
Abstract

2D PIC simulations for fast ignition with a planar target and an ultrahigh intensity laser have been performed to investigate effects of laser temporal profile on fast electron characteristics. Six different laser profiles, which are combination of two pulse shapes, namely Flattop and Gaussian shapes, and three different maximum intensities 1 × 1020, 5 × 1019, and 2.5 × 1019 W/cm2, are studied under the condition of fixed laser energy. Time-integrated energy spectra, coupling efficiencies from the heating laser to fast electrons, and divergence angle of fast electrons are shown and discussed.

Published
2013
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6. Efficient multi-keV X-ray generation from high-contrast laser plasma interaction

Author

Zhang Z., Nishimura H., Nishikino M., Sunahara A., Johzaki T., Cai H.B., Kawachi T., Pirozhkov A.S., Sagisaka A., Orimo S., Ogura K., Yogo A., Okano Y., Ohshima S., Fujioka S., Kiriyama H., Kondo K., Shimomura T., and Kanazawa S.

Subjects
Physics, QC1-999
Abstract

Kα line emission from Mo was experimentally and theoretically studied using clean, ultrahigh-intensity femtosecond laser pulses. The absolute yields of Kα x-rays at 17 keV from Mo were measured as a function of the laser pulse contrast ratio and irradiation intensity. Significantly enhanced Kα yields were obtained by employing high contrast ratio at optimum irradiance. Conversion efficiencies of 4.28 × 10−5/sr, the highest values obtained to date, was demonstrated with contrast ratios in the range of 10−10 to 10−11.

Published
2013
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8. Laser-ion acceleration via anomalous electron heating

Author

Yogo, A., Mima, K., Iwata, N., Tosaki, S., Morace, A., Arikawa, Y., Fujioka, S., Nishimura, H., Sagisaka, A., Johzaki, T., Matsuo, K., Kamitsukasa, N., Kojima, S., Nagatomo, H., Nakai, M., Shiraga, H., Murakami, M., Tokita, S., Kawanaka, J., Miyanaga, N., Yamanoi, K., Norimatsu, T., Sakagami, H., Bulanov, S. V., Kondo, K., and Azechi, H.

Subjects
Physics - Plasma Physics
Abstract

Using a kilojoule class laser, we demonstrate for the first time that high-contrast picosecond pulses are advantageous for ion acceleration. We show that a laser pulse with optimum duration and a large focal spot accelerates electrons beyond the ponderomotive energy. This anomalous electron heating enables efficient ion acceleration reaching 52 MeV at an intensity of 1.2X10^19 Wcm^-2. The proton energy observed agrees quantitatively with a one-dimensional plasma expansion model newly developed by taking the anomalous heating effect into account. The heating process is confirmed by both measurements with an electron spectrometer and a one-dimensional particle-in-cell simulation. By extending the pulse duration to 6 ps, 5% energy conversion efficiency to protons (50 J out of 1 kJ laser energy) is achieved with an intensity of 10^18-Wcm^-2. The present results are quite encouraging for realizing ion-driven fast ignition and novel ion beamlines., Comment: This paper has been withdrawn by the author to revise the theoretical model on the ion acceleration

Published
2016

9. Integrated simulation of magnetic-field-assist fast ignition laser fusion

Author

Johzaki, T., Nagatomo, H., Sunahara, A., Sakagami, Y. Sentoku. H., Hata, M., Taguchi, T., Mima, K., Kai, Y., Ajimi, D., Isoda, T., Endo, T., Yogo, A., Arikawa, Y., Fujioka, S., Shiraga, H., and Azechi, H.

Subjects
Physics - Plasma Physics
Abstract

To enhance the core heating efficiency in fast ignition laser fusion, the concept of relativistic electron beam guiding by external magnetic fields was evaluated by integrated simulations for FIREX class targets. For the cone-attached shell target case, the core heating performance is deteriorated by applying magnetic fields since the core is considerably deformed and the most of the fast electrons are reflected due to the magnetic mirror formed through the implosion. On the other hand, in the case of cone-attached solid ball target, the implosion is more stable under the kilo-tesla-class magnetic field. In addition, feasible magnetic field configuration is formed through the implosion. As the results, the core heating efficiency becomes double by magnetic guiding. The dependence of core heating properties on the heating pulse shot timing was also investigated for the solid ball target., Comment: 9pages, 12 figures, submitted to Plasma Physics and Controlled Fusion

Published
2016
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10. Control of Electron Beam Using Strong Magnetic Field for Efficient Core Heating in Fast Ignition

Author

Johzaki, T., Taguchi, T., Sentoku, Y., Sunahara, A., Nagatomo, H., Sakagami, H., Mima, K., Fujioka, S., and Shiraga, H.

Subjects
Physics - Plasma Physics
Abstract

For enhancing the core heating efficiency in electron-driven fast ignition, we proposed the fast electron beam guiding using externally applied longitudinal magnetic fields. Based on the PIC simulations for the FIREX-class experiments, we demonstrated the sufficient beam guiding performance in the collisional dense plasma by kT-class external magnetic fields for the case with moderate mirror ratio (~<10 ). Boring of the mirror field was found through the formation of magnetic pipe structure due to the resistive effects, which indicates a possibility of beam guiding in high mirror field for higher laser intensity and/or longer pulse duration., Comment: 11pages, 8figures

Published
2014
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13. Laser-plasma interactions for fast ignition

Author

Kemp, A. J., Fiuza, F., Debayle, A., Johzaki, T., Mori, W. B., Patel, P. K., Sentoku, Y., and Silva, L. O.

Subjects
Physics - Plasma Physics
Abstract

In the electron-driven fast-ignition approach to inertial confinement fusion, petawatt laser pulses are required to generate MeV electrons that deposit several tens of kilojoules in the compressed core of an imploded DT shell. We review recent progress in the understanding of intense laser plasma interactions (LPI) relevant to fast ignition. Increases in computational and modeling capabilities, as well as algorithmic developments have led to enhancement in our ability to perform multi-dimensional particle-in-cell (PIC) simulations of LPI at relevant scales. We discuss the physics of the interaction in terms of laser absorption fraction, the laser-generated electron spectra, divergence, and their temporal evolution. Scaling with irradiation conditions such as laser intensity are considered, as well as the dependence on plasma parameters. Different numerical modeling approaches and configurations are addressed, providing an overview of the modeling capabilities and limitations. In addition, we discuss the comparison of simulation results with experimental observables. In particular, we address the question of surrogacy of today's experiments for the full-scale fast ignition problem., Comment: 48 pages, 13 figures, submitted to Nuclear Fusion

Published
2013
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14. Theory of Fast Electron Transport for Fast Ignition

Author

Robinson, A. P. L., Strozzi, D. J., Davies, J. R., Gremillet, L., Honrubia, J. J., Johzaki, T., Kingham, R. J., Sherlock, M., and Solodov, A. A.

Subjects
Physics - Plasma Physics
Abstract

Fast Ignition Inertial Confinement Fusion is a variant of inertial fusion in which DT fuel is first compressed to high density and then ignited by a relativistic electron beam generated by a fast (< 20 ps) ultra-intense laser pulse, which is usually brought in to the dense plasma via the inclusion of a re-entrant cone. The transport of this beam from the cone apex into the dense fuel is a critical part of this scheme, as it can strongly influence the overall energetics. Here we review progress in the theory and numerical simulation of fast electron transport in the context of Fast Ignition. Important aspects of the basic plasma physics, descriptions of the numerical methods used, a review of ignition-scale simulations, and a survey of schemes for controlling the propagation of fast electrons are included. Considerable progress has taken place in this area, but the development of a robust, high-gain FI `point design' is still an ongoing challenge., Comment: 78 pages, 27 figures, review article submitted to Nuclear Fusion

Published
2013
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15. Effects of hydrogen concentration in ablator material on stimulated Raman scattering, two-plasmon decay, and hot electrons for direct-drive inertial confinement fusion

Author

Kawasaki, K., primary, Cristoforetti, G., additional, Idesaka, T., additional, Hironaka, Y., additional, Tanaka, D., additional, Batani, D., additional, Fujioka, S., additional, Gizzi, L. A., additional, Hata, M., additional, Johzaki, T., additional, Katagiri, K., additional, Kodama, R., additional, Matsuo, S., additional, Nagatomo, H., additional, Nicolai, Ph., additional, Ozaki, N., additional, Sentoku, Y., additional, Takizawa, R., additional, Yogo, A., additional, Yamada, H., additional, and Shigemori, K., additional

Published
2023
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21. Integrated experiments of fast ignition targets by Gekko-XII and LFEX lasers

Author

Shiraga, H., Fujioka, S., Nakai, M., Watari, T., Nakamura, H., Arikawa, Y., Hosoda, H., Nagai, T., Koga, M., Kikuchi, H., Ishii, Y., Sogo, T., Shigemori, K., Nishimura, H., Zhang, Z., Tanabe, M., Ohira, S., Fujii, Y., Namimoto, T., Sakawa, Y., Maegawa, O., Ozaki, T., Tanaka, K.A., Habara, H., Iwawaki, T., Shimada, K., Nagatomo, H., Johzaki, T., Sunahara, A., Murakami, M., Sakagami, H., Taguchi, T., Norimatsu, T., Homma, H., Fujimoto, Y., Iwamoto, A., Miyanaga, N., Kawanaka, J., Jitsuno, T., Nakata, Y., Tsubakimoto, K., Sueda, K., Morio, N., Matsuo, S., Kawasaki, T., Sawai, K., Tsuji, K., Murakami, H., Kanabe, T., Kondo, K., Kodama, R., Sarukura, N., Shimizu, T., Mima, K., and Azechi, H.

Published
2012
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22. Present states and future prospect of fast ignition realization experiment (FIREX) with Gekko and LFEX Lasers at ILE

Author

Koga, Mayuko, Arikawa, Y., Azechi, H., Fujimoto, Y., Fujioka, S., Habara, H., Hironaka, Y., Homma, H., Hosoda, H., Jitsuno, T., Johzaki, T., Kawanaka, J., Kodama, R., Mima, K., Miyanaga, N., Murakami, M., Nagatomo, H., Nakai, M., Nakata, Y., Nakamura, H., Nishimura, H., Norimatsu, T., Sakawa, Y., Sarukura, N., Shigemori, K., Shiraga, H., Shimizu, T., Takabe, H., Tanabe, M., Tanaka, K.A., Tanimoto, T., Tsubakimoto, T., Watari, T., Sunahara, A., Isobe, M., Iwamoto, A., Mito, T., Motojima, O., Ozaki, T., Sakagami, H., Taguchi, T., Nakao, Y., Cai, H., Key, M., Norreys, P., and Pasley, J.

Published
2011
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23. Ten hertz bead pellet injection and laser engagement

Author

Mori, Y., primary, Ishii, K., additional, Hanayama, R., additional, Okihara, S., additional, Kitagawa, Y., additional, Nishimura, Y., additional, Komeda, O., additional, Hioki, T., additional, Motohiro, T., additional, Sunahara, A., additional, Sentoku, Y., additional, Iwamoto, A., additional, Sakagami, H., additional, Miura, E., additional, and Johzaki, T., additional

Published
2022
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27. Improvement of ignition and burning target design for fast ignition scheme

Author

Nagatomo, H., Johzaki, T., Masayasu, Hata, Sentoku, Y., Fujioka, S., Mima, K., and Sakagami, H.

Abstract

For the fast ignition scheme of laser fusion, a highly compressed fuel core is necessary using a cone-inserted spherical solid target. We design an optimal compression method with a multistep laser pulse shape using a 2D radiation hydrodynamics simulation. In the design, the maximum areal density is ρRmax = 0.46 g cm−2 with 8 kJ of implosion laser. Considering the scaling law of hydrodynamic, we obtained 82 kJ and 1.3 MJ for the ignition-scale-target (ρRmax = 1.1 g cm−2) and burning-scale-target (ρRmax = 2.5 g cm−2), respectively. In a preliminary study of hydrodynamic instability in the optimized cone-inserted implosion, there is no significant growth of the instabilities that affect the implosion performance. A parameter search to investigate the feasibility and robustness of a high areal density design for changes in the laser pulse shape is performed. As a result, a delay of several tens of pico-second of the rising laser pulse is acceptable.

Published
2021

31. Anomalous enhancement of water window X-rays emitted from laser produced Au plasma under low-pressure nitrogen atmosphere

Author

Namba, S., John C., Kakunaka, N., Matsumoto, Y., Higashiguchi, T., Ejima, T., Sunahara, A., and Johzaki, T.

Abstract

Water window (WW) soft X-ray (wavelength: 2.3-4.4 nm) is a suitable light source for observing nanometer-size structure of living cells and bio-molecules. Although laser produced plasma has been expected as a bright and short pulse X-ray source, the conversion efficiency from driving laser pulse energy to WW radiation is far below 1%, which hinders the realization of a compact and low-cost X-ray microscope. Recently, it was found that the WW radiation increased, when an Au target was irradiated by the GEKKO XII laser (1053 nm, 500 ps, 120 J) under low-pressure nitrogen atmospheres up to 400 Pa. However, the fact that the laser facility is huge and its repetition rate is very low makes it impossible to apply this X-ray source to the microscope. In order to realize the practical microscope capable of reducing size and cost, The bright X rays generated with a joule class pulsed laser with a high repetition rate is essential. Therefore, under N2 atmospheres we measured the WW spectra emitted from Au plasma generated with a commercial nanosecond laser with a low-output energy and 10Hz-repwtition., 2nd Asia-Pacific Conference on Plasma Physics (AAPPS-DPP2018)

Published
2018

32. Water window soft X-ray emission from Au plasmas generated with a picosecond laser pulse

Author

Kakunaka, N., John, C., Matsumoto, Y., Higashiguch, T., Ejima, T., Sunahara, A., Nakajima, F., Johzaki, T., Endo, T., and Namba, S.

Abstract

Water window (WW) soft X-rays (wavelength 2.3 to 4.4 nm) are easily absorbed by carbon and are hardly absorbed by water around the living cells. Therefore, X-ray microscopy using WW soft X-ray is expected as a technology for observing nanometer scale structure of living cells. In order to obtain a high spatial resolution image with a soft X-ray microscope, a high intensity soft X-ray source is necessary, and usually high-power lasers of 10 J or more is indispensable. This is a major obstacle to spread and development of soft X-ray microscopes in medical and biological research fields. Recently, it has been found that when a gold target is irradiated with a commercial Nd:YAG laser (1064 nm, 7 ns, 1 J) under low-pressure nitrogen atmospheres up to 400 Pa, Soft X rays intensity emitted from plasmas increase significantly. Accordingly, a compact and low-cost X-ray microscope can be expected. In this study, in order to generate hot dense plasmas emitting much bright X-ray radiation, picosecond lasers with 10-ps and 500-ps pulse durations were employed. Gas fill circumstance is achieved by introducing nitrogen gas using a mass flow controller. For the soft X-ray measurement, a grazing incidence spectrometer (flat field grating of 2400 grooves / mm) with a toroidal focusing mirror is used. A pinhole camera with an aperture of 0-micron in diameter is also installed to measure two-dimensional X-ray imaging (magnification of 14×). To block the out-of-band radiation, appropriate thin filters are inserted in the pinhole tube. In this presentation, we will also report the influence on nitrogen gas fill circumstances by using picosecond laser pulses., 2nd Asia-Pacific Conference on Plasma Physics (AAPPS-DPP2018)

Published
2018

37. Boosting laser-ion acceleration with multi-picosecond pulses

Author

Yogo, A., primary, Mima, K., additional, Iwata, N., additional, Tosaki, S., additional, Morace, A., additional, Arikawa, Y., additional, Fujioka, S., additional, Johzaki, T., additional, Sentoku, Y., additional, Nishimura, H., additional, Sagisaka, A., additional, Matsuo, K., additional, Kamitsukasa, N., additional, Kojima, S., additional, Nagatomo, H., additional, Nakai, M., additional, Shiraga, H., additional, Murakami, M., additional, Tokita, S., additional, Kawanaka, J., additional, Miyanaga, N., additional, Yamanoi, K., additional, Norimatsu, T., additional, Sakagami, H., additional, Bulanov, S. V., additional, Kondo, K., additional, and Azechi, H., additional

Published
2017
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39. Integrated simulation of magnetic-field-assist fast ignition laser fusion

Author

Johzaki, T, primary, Nagatomo, H, additional, Sunahara, A, additional, Sentoku, Y, additional, Sakagami, H, additional, Hata, M, additional, Taguchi, T, additional, Mima, K, additional, Kai, Y, additional, Ajimi, D, additional, Isoda, T, additional, Endo, T, additional, Yogo, A, additional, Arikawa, Y, additional, Fujioka, S, additional, Shiraga, H, additional, and Azechi, H, additional

Published
2016
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41. Plasma structure and energy dependence in a magnetic thrust chamber system

Author

Morita, T, primary, Yamamoto, N., additional, Kawashima, R, additional, Saito, N, additional, Edamoto, M, additional, Fujioka, S, additional, Itadani, Y, additional, Johzaki, T, additional, Miura, S, additional, Mori, Y, additional, Nishimura, H, additional, Sunahara, A, additional, Yogo, A, additional, and Nakashima, H, additional

Published
2016
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42. Direct heating of compressed core by ultra-intense laser

Author

Sunahara, A, primary, Johzaki, T, additional, Sakagami, H, additional, Nagatomo, H, additional, Mima, K, additional, Abe, Y, additional, Arikawa, Y, additional, Fujioka, S, additional, Shiraga, H, additional, Azechi, H, additional, Mori, Y, additional, Sentoku, Y, additional, and Kitagawa, Y, additional

Published
2016
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45. Quantitative Kα line spectroscopy for energy transport in ultra-intense laser plasma interaction

Author

Zhang, Z., primary, Nishimura, H., additional, Fujioka, S., additional, Arikawa, Y., additional, Nakai, M., additional, Chen, H., additional, Park, J., additional, Williams, G. J., additional, Ozaki, T., additional, Shiraga, H., additional, Kojima, S., additional, Johzaki, T., additional, Sunahara, A., additional, Miyanaga, N., additional, Kawanaka, J., additional, Nakata, Y., additional, Jitsuno, T., additional, and Azechi, H., additional

Published
2016
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50. Stopping of α particles from the core in corona plasmas

Author

Mima, Kunioki, Tajima, Toshiki, Alvarez Ruiz, Jesus, Tanaka, K.A., Perlado Martín, José Manuel, Nagatomo, H., Johzaki, T., and Sunahara, A.

Subjects
Physics::Plasma Physics, Energía Nuclear, Optica
Abstract

In the laser fusion reactor design, the protection of first wall and the final optics from high energy ions is the key issue. So, it is necessary to predict the precise energy spectra of ions.In the previous reactor designs, the ion energy spectra were provided by the classical ion transport codes. However, this poster shows that the α particle spectrum is significantly modified by the anomalous process in ablated plasmas.

Published
2012

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