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Journal Articles

Stabilization of radiation reaction with vacuum polarization

Seto, Keita*; Zhang, S.*; Koga, J. K.; Nagatomo, Hideo*; Nakai, Mitsuo*; Mima, Kunioki*

Progress of Theoretical and Experimental Physics (Internet), 2014(4), p.043A01_1 - 043A01_10, 2014/04

 Times Cited Count:9 Percentile:37.04(Physics, Multidisciplinary)

Journal Articles

Theoretical study of ultrarelativistic laser-electron interaction with radiation reaction

Seto, Keita*; Nagatomo, Hideo*; Koga, J. K.; Taguchi, Toshihiro*; Mima, Kunioki*

EPJ Web of Conferences (Internet), 59, p.17020_1 - 17020_4, 2013/11

 Times Cited Count:0 Percentile:100

Journal Articles

Radiation reaction in ultrarelativistic laser-spinning electron interactions

Seto, Keita*; Nagatomo, Hideo*; Koga, J. K.; Mima, Kunioki*

Progress of Theoretical and Experimental Physics (Internet), 2013(5), p.053A01_1 - 053A01_10, 2013/05

 Times Cited Count:1 Percentile:86.3(Physics, Multidisciplinary)

Journal Articles

Effects to the industry by laser fusion study

Nakai, Sadao*; Izawa, Yasukazu*; Fujita, Masayuki*; Kondo, Kiminori; Daido, Hiroyuki; Mima, Kunioki*; Saso, Akihiro*

Oputoronikusu, 31(9), p.134 - 142, 2012/09

The laser fusion has a long history as a study with high intensity laser. There are many application fields which have been grown up from this laser fusion study. In this article, the various industrial applications related to the laser fusion technology, which are EUV light source, non-thermal processing, particle acceleration, neutron source, space application, and demolition and/or decontamination of nuclear plant, are explained.

Journal Articles

Theoretical study of ultra-relativistic laser electron interaction with radiation reaction by quantum description

Seto, Keita*; Nagatomo, Hideo*; Koga, J. K.; Mima, Kunioki*

Plasma and Fusion Research (Internet), 7(Sp.1), p.2404010_1 - 2404010_4, 2012/02

Journal Articles

Equation of motion with radiation reaction in ultrarelativistic laser-electron interactions

Seto, Keita*; Nagatomo, Hideo*; Koga, J. K.; Mima, Kunioki*

Physics of Plasmas, 18(12), p.123101_1 - 123101_8, 2011/12

 Times Cited Count:9 Percentile:55.23(Physics, Fluids & Plasmas)

Journal Articles

Experimental evidence of nonthermal acceleration of relativistic electrons by an intensive laser pulse

Kuramitsu, Yasuhiro*; Nakanii, Nobuhiko*; Kondo, Kiminori; Sakawa, Yoichi*; Mori, Yoshitaka*; Miura, Eisuke*; Tsuji, Kazuki*; Kimura, Kazuya*; Fukumochi, Shuji*; Kashihara, Mamoru*; et al.

Physical Review E, 83(2), p.026401_1 - 026401_6, 2011/02

 Times Cited Count:13 Percentile:33.14(Physics, Fluids & Plasmas)

An energy distribution function of energetic particles in the universe or cosmic rays is well represented by a power-law spectrum, therefore, nonthermal acceleration is essential to understand the origin of cosmic rays. A possible candidate for the origin of cosmic rays is wakefield acceleration at relativistic astrophysical perpendicular shocks. Substituting an intensive laser pulse for the large amplitude light waves, we performed a model experiment of the shock environments in a laboratory plasma.

Journal Articles

Model experiment of cosmic ray acceleration due to an incoherent wakefield induced by an intense laser pulse

Kuramitsu, Yasuhiro*; Nakanii, Nobuhiko*; Kondo, Kiminori; Sakawa, Yoichi*; Mori, Yoshitaka*; Miura, Eisuke*; Tsuji, Kazuki*; Kimura, Kazuya*; Fukumochi, Shuji*; Kashihara, Mamoru*; et al.

Physics of Plasmas, 18(1), p.010701_1 - 010701_4, 2011/01

 Times Cited Count:16 Percentile:35.15(Physics, Fluids & Plasmas)

Substituting an intensive laser pulse for the large amplitude light waves, we performed a model experiment of the shock environments in a laboratory plasma. An intensive laser pulse was propagated in a plasma tube created by imploding a hollow polystyrene cylinder, as the large amplitude light waves propagated in the upstream plasma at an astrophysical shock. Nonthermal electrons were generated, and the energy distribution functions of the electrons have a power-law component with an index of 2.

Journal Articles

FIREX project and effects of self-generated electric and magnetic fields on electron-driven fast ignition

Mima, Kunioki*; Sunahara, Atsushi*; Shiraga, Hiroyuki*; Nishimura, Hiroaki*; Azechi, Hiroshi*; Nakamura, Tatsufumi; Jozaki, Tomoyuki*; Nagatomo, Hideo*; Garcia, C.*; Veralde, P.*

Plasma Physics and Controlled Fusion, 52(12), p.124047_1 - 124047_6, 2010/12

 Times Cited Count:9 Percentile:60.18(Physics, Fluids & Plasmas)

Fast ignition is a new scheme in laser fusion, in which higher energy gain with a smaller laser pulse energy is expected. At Osaka University, a laser with four beams and a total output of 10 kJ ps-1, laser for fast ignition experiment (LFEX), has been constructed and we have carried out an integrated experiment with one beam of the LFEX. Through experiments it was found that the coupling efficiency is degraded when the laser pre-pulse is not sufficiently small. Furthermore, the distance between the hot electron source and the core plasma is large. In this paper it is proposed that a thin foil covers the laser entrance of the cone to mitigate the pre-plasma and a double cone reduces the loss of high energy electrons from the side wall of the cone. The simulations indicate that a higher coupling efficiency is expected for the double cone target with a thin foil at the laser entrance.

Journal Articles

Correlation between laser accelerated MeV proton and electron beams using simple fluid model for target normal sheath acceleration

Tampo, Motonobu; Awano, Shinya*; Bolton, P.; Kondo, Kiminori; Mima, Kunioki*; Mori, Yoshitaka*; Nakamura, Hirotaka*; Nakatsutsumi, Motoaki*; Stephens, R. B.*; Tanaka, Kazuo*; et al.

Physics of Plasmas, 17(7), p.073110_1 - 073110_5, 2010/07

 Times Cited Count:10 Percentile:56.78(Physics, Fluids & Plasmas)

Journal Articles

Tomography of an ultrafast laser driven proton source

Ter-Avetisyan, S.*; Schn$"u$rer, M.*; Nickles, P. V.*; Sandner, W.*; Borghesi, M.*; Nakamura, Tatsufumi; Mima, Kunioki*

Physics of Plasmas, 17(6), p.063101_1 - 063101_6, 2010/06

 Times Cited Count:7 Percentile:67.78(Physics, Fluids & Plasmas)

Using a multichannel Thomson spectrometer we have implemented a tomographic approach allowing the reconstruction of the emission characteristics of a laser driven proton source with high energy and spatial resolution. The results demonstrate the complexity of the temporal and spatial characteristics of such a source. The emitted proton beam, which is laminar and divergent ant high energies, becomes convergent at low energies. This implies that a fraction of the proton beam having this kinetic energy is emitted in a collimated way from the target at the turning point between these tow behaviors. Only a finite fraction of the target surface is contributing to the ion spectrum, which is measured at a specific angle within the beam cone. Therefore the momentum distribution of the protons in the emitted beam at any point in space can be controlled by determining the proton source area.

Journal Articles

Correlation of spectral, spatial, and angular characteristics of an ultrashort laser driven proton source

Ter-Avetisyan, S.*; Schn$"u$rer, M.*; Nickles, P. V.*; Sandner, W.*; Nakamura, Tatsufumi; Mima, Kunioki*

Physics of Plasmas, 16(4), p.043108_1 - 043108_6, 2009/04

 Times Cited Count:24 Percentile:27.5(Physics, Fluids & Plasmas)

The laser driven ion source is highly organized dynamical system. It relies on a well defined interaction between the spatial and momentum distributions of emitted ions. This correlation is found by a consecutive spectral characterization of distinct proton beamlets emitted from different spatial target positions and under different angles. In case of a flat target and a perfectly round laser focal spot, the proton source is circular symmetric and each source point behaves similarly: the higher the proton energy the smaller the source size and the larger the emission angle for a similar source extension. Only the symmetry axis is unique; here all protons are emitted at 0$$^{circ}$$ to the target normal.

Journal Articles

Guiding and confining fast electrons by transient electric and magnetic fields with a plasma inverse cone

Lei, A. L.*; Cao, L. H.*; Yang, X. Q.*; Tanaka, Kazuo*; Kodama, Ryosuke*; He, X. T.*; Mima, Kunioki*; Nakamura, Tatsufumi; Norimatsu, Takayoshi*; Yu, W.*; et al.

Physics of Plasmas, 16(2), p.020702_1 - 020702_4, 2009/02

 Times Cited Count:11 Percentile:54.15(Physics, Fluids & Plasmas)

The fast electron propagation in an inverse cone target is investigated computationally and experimentally. Two-dimensional particle-in-cell simulation shows that fast electrons with substantial numbers are generated at the outer tip of an inverse cone target irradiated by a short intense laser pulse. These electrons are guided and confined to propagate along the inverse cone wall, forming a large surface current. The experiment qualitatively verifies the guiding and confinement of the strong electron current in the wall surface. The large surface current and induced strong field s are of importance for fast ignition related research.

Journal Articles

Hydrothermal-method-grown ZnO single crystal as fast EUV scintillator for future lithography

Nakazato, Tomoharu*; Furukawa, Yusuke*; Tanaka, Momoko; Tatsumi, Toshihiro*; Nishikino, Masaharu; Yamatani, Hiroshi*; Nagashima, Keisuke; Kimura, Toyoaki*; Murakami, Hidetoshi*; Saito, Shigeki*; et al.

Journal of Crystal Growth, 311(3), p.875 - 877, 2009/01

 Times Cited Count:23 Percentile:12.66(Crystallography)

The temperature dependence of scintillation properties of a hydrothermal-method-grown zinc oxide (ZnO) emission is investigated using a nickel-like silver laser emitting at 13.9 nm. A broad peak at 386 nm with a full-width at half-maximum (FWHM) of 15 nm at room temperature (298 K) is obtained. The peak position tends to be blue shifted while the FWHM becomes narrower when the crystal temperature is decreased to 25 K. Streak images fitted by a double exponential decay reveal that the measured emission decay at 105 K was $$tau$$$$_{1}$$ = 0.88 ns and $$tau$$$$_{2}$$ = 2.7 ns. This decay time of a few nanoseconds is suitable for lithographic applications and is sufficiently short for the characterization of laser plasma extreme ultraviolet (EUV) sources with nanosecond durations.

Journal Articles

ZnO as fast scintillators evaluated with Ni-like Ag laser

Furukawa, Yusuke*; Tanaka, Momoko; Murakami, Hidetoshi*; Saito, Shigeki*; Sarukura, Nobuhiko*; Nishikino, Masaharu; Yamatani, Hiroshi; Nishimura, Hiroaki*; Mima, Kunioki*; Kagamitani, Yuji*; et al.

Reza Kenkyu, 36(APLS), p.1028 - 1030, 2008/12

Optical technologies in extreme ultraviolet (EUV) region have been receiving strong interests for the next generation lithography. Here we report properties of ZnO as scintillators in the EUV region, and to demonstrate the feasibility of using a Ni-like Ag EUV laser operated at 13.9-nm to evaluate these properties. The ZnO sample was irradiated with EUV laser pulses and the fluorescence was measured using a streak camera fitted with a spectrograph. A clear, excitonic, fluorescence peak was observed at around 380 nm with a decay lifetime of 3 ns. The prominent peak fluorescence is ideal for EUV detection and further applications including imaging.

Journal Articles

Probing of nonlinear evolution of laser wakefield by Raman scattering of laser light

Zhou, W.*; Mima, Kunioki*; Nakamura, Tatsufumi; Nagatomo, Hideo*

Physics of Plasmas, 15(9), p.093107_1 - 093107_6, 2008/09

 Times Cited Count:7 Percentile:67.52(Physics, Fluids & Plasmas)

When a weak probe laser pulse is injected into a wakefield excited by a short high-intensity pump laser pulse, the probe pulse will be Raman scattered by the wakefield. It is possible to determine the density profile from the spectrum of this forward Raman scattered probe laser. In previous research, an analytical solution for the multiple sidebands of the forward Raman scattering of the probe laser pulse was presented. These multiple sidebands are connected with the steepening of density perturbation of the wakefield. More detailed information of the probe pulse in wakefield is studied with one-dimensional particle-in-cell simulations. The analytical solution and the results of simulation are consistent with each other and other experiments.

Journal Articles

Spectrum modulation of relativistic electrons by laser wakefield

Nakanii, Nobuhiko*; Kondo, Kiminori; Kuramitsu, Yasuhiro*; Mori, Yoshitaka*; Miura, Eisuke*; Tsuji, Kazuki*; Kimura, Kazuya*; Fukumochi, Shuji*; Kashihara, Mamoru*; Tanimoto, Tsuyoshi*; et al.

Applied Physics Letters, 93(8), p.081501_1 - 081501_3, 2008/08

 Times Cited Count:4 Percentile:79.15(Physics, Applied)

Energetic electrons were generated by the interaction of a high-intensity laser pulse with a plasma preformed from a hollow plastic cylinder via laser-driven implosion. The spectra of a comparatively high-density plasma had a bump around 10 MeV. Simple numerical calculations explained the spectra obtained in this experiment. This indicates that the plasma tube has sufficient potential to convert a Maxwellian spectrum to a comparatively narrow spectrum.

Journal Articles

Magnetic-dipole vortex generation by propagation of ultraintense and ultrashort laser pulses in moderate-density plasmas

Nakamura, Tatsufumi; Mima, Kunioki*

Physical Review Letters, 100(20), p.205006_1 - 205006_4, 2008/05

 Times Cited Count:28 Percentile:21.05(Physics, Multidisciplinary)

A magnetic dipole vortex is generated in the behind of an ultra-intense and ultra-short laser pulse in a near critical density plasma. The vortex is self-sustained by its magnetic field pressure which expels background cold electrons. This results in inducing a sheath field around the vortex which accelerates electrons to drive high amplitude electric current inside the vortex. The energy spectra of electrons accelerated in vortex shows non-thermal distribution with relatively high energy. The vortex is stable for a long period since it is in the electromagnetic equilibrium. The size of vortex and magnitude of electromagnetic fields are explained by a simple analytical model, which explains the characteristics of magnetic vortex in a wide parameter range. The results of analytical model show good agreements with 2D Particle-in-Cell simulation results. The high energy coupling of laser to electrons might be utilized for laser ion acceleration.

Journal Articles

Lateral movement of a laser-accelerated proton source on the target's rear surface

Nakamura, Tatsufumi; Mima, Kunioki*; Ter-Avetisyan, S.*; Schn$"u$rer, M.*; Sokollic, T.*; Nickles, P.*; Sandner, W.*

Physical Review E, 77(3), p.036407_1 - 036407_5, 2008/03

 Times Cited Count:12 Percentile:38.62(Physics, Fluids & Plasmas)

The spatial dependence of proton acceleration at the rear surface of a target which is irradiated by high contrast and ultra-intense laser pulses is investigated. Lateral movement of proton acceleration position at the rear surface is observed, which is proofed by two-pinhole measurement which results in the observation of protons with narrow energy band. This drifting is uniquely observed when relativistic intensity laser pulses irradiate targets with small pre-plasma with oblique incidence, which is confirmed by 2D-PIC simulations. This proton acceleration scenario by the fast moving sheath field leads to the energy selection of accelerated protons as a function of observing position.

Journal Articles

Evaluation of fast EUV scintillator using 13.9 nm X-ray laser

Tanaka, Momoko; Furukawa, Hiroyuki*; Murakami, Hidetoshi*; Saito, Shigeki*; Sarukura, Nobuhiko*; Nishikino, Masaharu; Yamatani, Hiroshi; Nagashima, Keisuke; Kagamitani, Yuji*; Ehrentraut, D.*; et al.

Journal of Physics; Conference Series, 112(4), p.042058_1 - 042058_4, 2008/00

 Times Cited Count:1 Percentile:40.32

Optical technologies in the extreme ultraviolet (EUV) region have been receiving strong interest for the next generation lithography. Efficient and fast scintillators are one of the key devices functioning in the EUV region. In this paper, we report excellent properties of ZnO and GaN as scintillators in the EUV region, and to demonstrate the feasibility of using a Ni-like Ag EUV laser operated at 13.9-nm to evaluate these properties. The sample was irradiated with EUV laser pulses, and the fluorescence spectrum and the fluorescence lifetime were measured using a streak camera fitted with a spectrograph. In the case of ZnO, a clear, excitonic, fluorescence peak was observed at around 380 nm with a decay lifetime of 3 ns. For GaN, a fluorescence peak at 370 nm having slower 5-ns decay time was observed. In this respect, the EUV scintillation properties of ZnO is said to be more favorable than GaN.

40 (Records 1-20 displayed on this page)