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量子メスのインジェクターの実用化に向けて、レーザー駆動イオン加速ビーム個数を定量的に計測する手法の開発が必要であった。本論文では、ビーム収束系とトムソンパラボラを組み合わせることで、イオン価数とエネルギーを分離しながらレンズ収束系を通過するイオン個数を求めるという方法の実証試験を行い、その実証結果が示されている。

量研関西研では,レーザー駆動イオン加速機構によって生じる炭素ビームの横方向エミッタンスを明らかにすることに取り組んでいる。同時加速される陽子ビームから炭素ビームを弁別することが困難であるために，炭素ビームの横方向エミッタンスが評価された例はない。現在, 四重極磁石による核種の磁場弁別とダブルスリット法とを組み合わせた炭素ビーム横方向エミッタンス診断系の開発を進めている。 本発表では, 数理的な考えを診断装置に組み込むことによる, 観測誤差の低減に関して報告する予定である。, 第69回応用物理学会春季学術講演会

近年，炭素イオンなどを用いた重イオンビームによるガン治療は成功を収めている．一般的に，直線もしくはシンクロトロン型の粒子加速器が高エネルギー重イオンビーム生成のために使用されるが，それらの加速器は広く医療機関に行き渡らせるにはサイズが大きすぎるという問題を持つ．そのためコンパクトな加速器の実現が求められている．レーザー粒子加速器は，未来の加速器の候補の一つである． 量子科学技術研究開発機構では，高い治療効果が明らかになっている重イオンがん治療装置の高性能化・小型化を目指す“量子メス”プロジェクトを進めている．この次世代の小型重イオンがん治療装置は，重イオンビームの鋭いブラッグピークと，少ない内部散乱による腫瘍への高い線量集中性を持っている．これによって正常組織へのダメージを少なく抑え，より多くのがんを極めて短期間で治療できることが期待され、手術に代わる可能性を秘めている． 現在提案されている第５世代重イオンがん治療装置（量子メス）は，イオン入射器・超伝導シンクロトロン・ビーム輸送系・超伝導回転ガントリーから構成されている．装置を小型化するためには，体積の大部分を占める入射器とシンクロトロンの小型化が不可欠である．レーザー駆動イオン加速は非常に大きな加速勾配を持つことからこの小型化の要求に応える技術として期待されている．既存のイオン入射器をレーザー駆動方式で置き換えるためには，小型のレーザーモジュールの開発とそれを用いたレーザー駆動による数MeV/uの炭素イオンの加速が必要である．そこで，三次元電磁粒子コードによって実験に即したシミュレーションを実施することにより，加速炭素イオンの定量評価を行った．また，加速に有利な６価の炭素イオンを生成するためのレーザー条件を理論的に求め，シミュレーションによる妥当性評価を行った．, 日本物理学会第77回年次大会

現在、レーザー駆動イオン加速は重粒子線がん治療用加速器のイオン入射器への応用が検討されている。本研究では、厚さ10umのニッケル上に300層のグラフェンを成膜した標的に 2×1019 W/cm2のレーザーパルスを照射することで、最大エネルギー0.5MeV/uの4価の炭素イオンを加速した。これは重粒子線がん治療用加速器のイオン入射器の前段として機能するRFQ加速器の引き出しエネルギーに匹敵する。, 2021年度ビーム物理研究会、若手の会

A counter-propagating laser-beam platform using a spherical plasma mirror was developed for the kilojoule-class petawatt LFEX laser. The temporal and spatial overlaps of the incoming and redirected beams were measured with an optical interferometer and an x-ray pinhole camera. The plasma mirror performance was evaluated by measuring fast electrons, ions, and neutrons generated in the counter-propagating laser interaction with a Cu-doped deuterated film on both sides. The reflectivity and peak intensity were estimated as ∼50% and ∼5 × 1018 W/cm2, respectively. The platform could enable studies of counter-streaming charged particles in high-energy-density plasmas for fundamental and inertial confinement fusion research.

In the counter-irradiation, which is one of the fast ignition schemes, higher core energy coupling can be expected when there are two hot electron flows in counter directions. Two plasma mirrors were installed for the counter irradiation at about 180 degrees. The hot electron effective temperatures (Teff) were measured by using electron energy spectrometers. Teff vs the laser intensity on a foil target followed Wilkes' scaling law. The energy incident on the target could be calculated by estimating the laser intensity on the target from Teff and estimating the focusing radius from the X-ray pinhole camera image. As a result, the reflectivity could be estimated to be 17 ± 3%.

量研・ 関西研では 、超電導シンクロトロンとレーザー駆動炭素インジェクターを組み合わせた重粒子線治療装置の量子メスの開発を進めている。この開発では、 TNSA 法 により、4MeV/ 核子の炭素を発生させ入射することを目標としているが、レーザー駆動加速イオンの特徴であるピコ秒領域の極短パルス大電流という炭素ビームが「ビーム輸送系を介して超伝導 シンクロトロン のアクセプタンスに入射できるのか」という点については十分な検討がされていない。そこで、ビーム診断系および輸送系コンポーネント（磁石、静電レンズ）通過時 に生じる磁場および電場（空間電荷効果以外の外力）による 非線形性の増大に関して計算できるように整備した。今回はそれらの 結果と、量子メス実験用プラットホームでペッパーポット式のエミッタンスモニタで求めた数十keV級低エネルギーのイオンビームのエミッタンス量の結果を比較検討したので報告する。, 日本物理学会第76回年次大会

Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive and alternative approach to create ultra-high-energy-density states like those found in inertial confinement fusion (ICF) ignition sparks. Laser-produced relativistic electron beam (REB) deposits a part of kinetic energy in the core, and then the heated region becomes the hot spark to trigger the ignition. However, due to the inherent large angular spread of the produced REB, only a small portion of the REB collides with the core. Here, we demonstrate a factor-of-two enhancement of laser-to-core energy coupling with the magnetized fast isochoric heating. The method employs a magnetic field of hundreds of Tesla that is applied to the transport region from the REB generation zone to the core which results in guiding the REB along the magnetic field lines to the core. This scheme may provide more efficient energy coupling compared to the conventional ICF scheme., It is desirable to deposit more energy in the dense plasma core to trigger the fusion ignition. Here the authors demonstrate enhanced energy coupling from laser to plasma core by using solid targets and guiding the transport of relativistic electron beam with external magnetic field.

Alpha particles generated by

Collective Thomson scattering (CTS) has been applied to laser-produced plasmas with Gekko XII HIPER laser facility. A scheme of stimulated Brillouin scattering (SBS) has been used in CTS measurements for the first time. Utilizing SBS shortens the probe pulse, which increases the scattered power, and thus collected scattered signal of CTS. Therefore, a lower energy probe laser can be used for given background emission levels to avoid probe heating, which is crucial for plasmas with low electron temperature. Both electron and ion features of CTS have been successfully detected by using the SBS technique. The spatial profile of electron density, temperature, and drift velocity have been estimated in an ablation plasma. In addition to the local measurements with CTS, a global structure of plasmas has been obtained with optical imaging of the self-emission of plasmas and the interferometry. In the aspects of drift velocity and plasma density, the local and global information are in good agreement.

Fast isochoric laser heating is a scheme to heat a matter with relativistic-intensity ($>$ 10$^{18}$ W/cm$^2$) laser pulse or X-ray free electron laser pulse. The fast isochoric laser heating has been studied for creating efficiently ultra-high-energy-density (UHED) state. We demonstrate an fast isochoric heating of an imploded dense plasma using a multi-picosecond kJ-class petawatt laser with an assistance of externally applied kilo-tesla magnetic fields for guiding fast electrons to the dense plasma.The UHED state with 2.2 Peta-Pascal is achieved experimentally with 4.6 kJ of total laser energy that is one order of magnitude lower than the energy used in the conventional implosion scheme. A two-dimensional particle-in-cell simulation reveals that diffusive heating from a laser-plasma interaction zone to the dense plasma plays an essential role to the efficient creation of the UHED state., 8 pages, 4 figures, 1 table

Intense lasers interacting with dense targets accelerate relativistic electron beams, which transport part of the laser energy into the target depth. However, the overall laser-to-target energy coupling efficiency is impaired by the large divergence of the electron beam, intrinsic to the laser–plasma interaction. Here we demonstrate that an efficient guiding of MeV electrons with about 30 MA current in solid matter is obtained by imposing a laser-driven longitudinal magnetostatic field of 600 T. In the magnetized conditions the transported energy density and the peak background electron temperature at the 60-μm-thick target's rear surface rise by about a factor of five, as unfolded from benchmarked simulations. Such an improvement of energy-density flux through dense matter paves the ground for advances in laser-driven intense sources of energetic particles and radiation, driving matter to extreme temperatures, reaching states relevant for planetary or stellar science as yet inaccessible at the laboratory scale and achieving high-gain laser-driven thermonuclear fusion., Efficient energy transport by laser-driven relativistic electron beams is crucial in many applications including inertial confinement fusion, and particle acceleration. Here the authors demonstrate relativistic electron beam guiding in dense plasma with an externally imposed high magnetic field.

Frequency-resolved optical gating (FROG) is a novel means of measuring the fast motion of a critical density surface during relativistic laser–plasma interaction. Herein, we present a design and demonstration results for a new single-shot FROG system and optical transport system for characterizing the instantaneous intensity and phase at the LFEX (Laser for Fast Ignition Experiment) laser facility at the Institute of Laser Engineering of Osaka University. At LFEX, the laser intensity at the vacuum window is intrinsically high because of two unique properties, namely, the large F-number of the off-axis parabolic mirror and the small radius of the interaction chamber. Consequently, to obtain an accurate FROG trace, attention must be paid to spectrum modulation due to self-phase modulation. The appropriate laser intensity for FROG operation was investigated experimentally, and an optical transport system with an energy attenuator composed of reflective optics was designed to eliminate the concern of spectrum modulation from measurements. A FROG trace recorded at LFEX shot with 161 J energy was reconstructed 100 times using an iterative phase-retrieval algorithm. Despite some differences in structure, the reconstructed spectrum agrees reasonably well with the spectrum obtained by a time-integrated spectrometer. This shows that the developed FROG system and the optical transport system can measure the instantaneous intensity and phase of a laser pulse without spectrum modulation.

To understand the changes in the optical properties of a titanium surface induced by irradiation with low-intensity laser light that does not cause surface peeling, we have proposed a pump-and-probe method using femtosecond laser pulses with fluences below and above the ablation threshold (BAT and AAT, respectively). By analyzing the dependence of the ablation rate on the AAT probe-pulse fluence, the dynamical changes in the effective laser penetration depth and effective ablation threshold could be estimated. The dependences of the effective laser penetration depth and effective ablation threshold on the pump-pulse fluence Fpump below the ablation threshold Fth (Fpump 0.18 Fth reduced both the effective laser penetration depth and effective ablation threshold compared with irradiation without the pump pulse. The obtained results also indicated a large reduction in the effective laser penetration depth (58% for Fpump = 0.9 Fth) and a small reduction in the effective ablation threshold (15% for Fpump = 0.9 Fth).

This article reports the development of a compact Thomson parabola spectrometer for laser-accelerated ions that can measure angular distribution with a high energy resolution and has a variable measurable energy range. The angular-resolved energy spectra for different ion species can be measured in a single shot, and the sampling angle can be selected from outside the vacuum region. The electric and magnetic fields are applied to the ion dispersion by using a permanent magnetic circuit and annulus sector-shaped electrodes with a wedge configuration. The compact magnetic circuit consists of permanent magnets, fixed yokes, and movable yokes. The magnetic flux is intentionally leaked to the movable yokes, allowing the magnetic field to be adjusted from 53 mT to 259 mT. The annulus sector-shaped electrodes with a wedge configuration provide better trace separation for high-energy ions, retain the lower-energy part of the ion signal, and subject ions passing through all pinholes to an equivalent Lorentz force. The magnetic and electric fields are designed for measuring protons and carbon ions with an energy range of 0.1-5 MeV. The spectrometer allows for the adjustment of the observable energy range afterward according to the parameters of the accelerated ion.

Increasing the laser energy absorption into energetic particle beams represents a longstanding quest in intense laser-plasma physics. During the interaction with matter, part of the laser energy is converted into relativistic electron beams, which are the origin of secondary sources of energetic ions, γ-rays and neutrons. Here we experimentally demonstrate that using multiple coherent laser beamlets spatially and temporally overlapped, thus producing an interference pattern in the laser focus, significantly improves the laser energy conversion efficiency into hot electrons, compared to one beam with the same energy and nominal intensity as the four beamlets combined. Two-dimensional particle-in-cell simulations support the experimental results, suggesting that beamlet interference pattern induces a periodical shaping of the critical density, ultimately playing a key-role in enhancing the laser-to-electron energy conversion efficiency. This method is rather insensitive to laser pulse contrast and duration, making this approach robust and suitable to many existing facilities., Enhanced coupling of laser energy to the target particles is a fundamental issue in laser-plasma interactions. Here the authors demonstrate increased photon absorption leading into higher laser to electron and proton energy transfer through the interference of multiple coherent beamlets.

High-power lasers in the relativistic intensity regime with multi-picosecond pulse durations are available in many laboratories around the world. Laser pulses at these intensities reach giga-bar level radiation pressures, which can push the plasma critical surface where laser light is reflected. This process is referred to as the laser hole boring (HB), which is critical for plasma heating, hence essential for laser-based applications. Here we derive the limit density for HB, which is the maximum plasma density the laser can reach, as a function of laser intensity. The time scale for when the laser pulse reaches the limit density is also derived. These theories are confirmed by a series of particle-in-cell simulations. After reaching the limit density, the plasma starts to blowout back toward the laser, and is accompanied by copious superthermal electrons; therefore, the electron energy can be determined by varying the laser pulse length., Different energy transport mechanisms come into play when intense laser pulses interact with dense plasma. Here the authors provide a limit on the plasma density reachable with an intense laser and an insight into the hole boring process.

A relativistic laser pulse, confined in a cylindrical-like target, under specific conditions may perform multiple scattering along the internal target surface. This results in the confinement of the laser light, leading to a very efficient interaction. The demonstrated propagation of the laser pulse along the curved surface is just yet another example of the “whispering gallery” effect, although nonideal due to laser–plasma coupling. In the relativistic domain its important feature is a gradual intensity decrease, leading to changes in the interaction conditions. The process may pronounce itself in plenty of physical phenomena, including very efficient electron acceleration and generation of relativistic magnetized plasma structures.

Powerful laser-plasma processes are explored to generate discharge currents of a few $100\,$kA in coil targets, yielding magnetostatic fields (B-fields) in excess of $0.5\,$kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, describing qualitatively the evolution of the discharge current, the major control parameter is the laser irradiance $I_{\mathrm{las}}\lambda_{\mathrm{las}}^2$. The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and by proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport into solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at $60 \,\mathrm{\mu m}$ depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes and to laboratory astrophysics., Comment: 11 pages, 7 figures, invited APS

Quantitative high-energy X-ray spectroscopy is applied for the laser plasma interaction in the fast ignition scheme. A double tracer layer target is designed for the absolute measurement of hot electron temperature and laser energy transfer efficiency. The hot electron temperature is determined from the ratio of the number of K α photons from the first and second tracers. Consequently, the energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived. In a cone-guide geometry, we simultaneously measured the hot electron temperature and the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, which were measured to be 5.3 MeV and 37%, respectively.

Recent progress in the generation in the laboratory of a strong ($g100$-T) magnetic field enables us to investigate experimentally unexplored magnetohydrodynamics phenomena of a high-energy-density plasma, which an external magnetic field of 200--300 T notably affects due to anisotropic thermal conduction, even when the magnetic field pressure is much lower than the plasma pressure. The external magnetic field reduces electron thermal conduction across the external magnetic field lines because the Larmor radius of the thermal electrons in the external magnetic field is much shorter than the mean free path of the thermal electrons. The velocity of a thin polystyrene foil driven by intense laser beams in the strong external magnetic field is faster than that in the absence of the external magnetic field. Growth of sinusoidal corrugation imposed initially on the laser-driven polystyrene surface is enhanced by the external magnetic field because the plasma pressure distribution becomes nonuniform due to the external magnetic-field structure modulated by the perturbed plasma flow ablated from the corrugated surface.

Using one of the world most powerful laser facility, we demonstrate for the first time that high-contrast multi-picosecond pulses are advantageous for proton acceleration. By extending the pulse duration from 1.5 to 6 ps with fixed laser intensity of 1018 W cm−2, the maximum proton energy is improved more than twice (from 13 to 33 MeV). At the same time, laser-energy conversion efficiency into the MeV protons is enhanced with an order of magnitude, achieving 5% for protons above 6 MeV with the 6 ps pulse duration. The proton energies observed are discussed using a plasma expansion model newly developed that takes the electron temperature evolution beyond the ponderomotive energy in the over picoseconds interaction into account. The present results are quite encouraging for realizing ion-driven fast ignition and novel ion beamlines.

Alpha particles generated by 7Li(p,α)4He and 19F(p,α)16O reactions are selectively detected in the presence of abundant primary protons by reducing the proton sensitivity of CR-39 using a potassium hydroxide-ethanol-water (PEW) etching solution. These nuclear reactions are induced in a LiF crystal using the laser-accelerated protons (4 × 1011 protons/pulse with a maximum energy of 3.3 MeV) generated and accelerated by the interaction of a 40-fs laser pulse with a polyethylene thin film target at a peak intensity of 5 × 1019 W/cm2. Subsequent etching of the CR-39 in the PEW solution (KOH: 17 wt. %; C2H5OH: 25 wt. %; H2O: 58 wt. %) permits the selective detection of 4.0 MeV alpha particles, which is independently confirmed by an experiment using alpha particles from an 241Am source. The described method is expected to be useful for research into nuclear reactions in laser plasma.

Absolute Kα line spectroscopy is proposed for studying laser–plasma interactions taking place in the Au cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100 keV were quantitatively measured with a Laue spectrometer composed of a cylindrically curved crystal and a filter-absorption method for Bremsstrahlung continuum emission. The absolute sensitivities of the Laue spectrometer systems were calibrated using pre-characterized laser-produced X-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an X-ray diffraction code. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived from this work. The absolute yield of Au and Ta Kα lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from electron spectrometer and scaling laws, the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, to hot electrons was derived for the first time.

Hard X-ray spectroscopy is an essential diagnostics used to understand physical processes that take place in high energy density plasmas produced by intense laser-plasma interactions. A bundle of hard X-ray detectors, of which the responses have different energy thresholds, is used as a conventional single-shot spectrometer for high-flux (>10(13) photons/shot) hard X-rays. However, high energy resolution (Δhv/hv < 0.1) is not achievable with a differential energy threshold (DET) X-ray spectrometer because its energy resolution is limited by energy differences between the response thresholds. Experimental demonstration of a Compton X-ray spectrometer has already been performed for obtaining higher energy resolution than that of DET spectrometers. In this paper, we describe design details of the Compton X-ray spectrometer, especially dependence of energy resolution and absolute response on photon-electron converter design and its background reduction scheme, and also its application to the laser-plasma interaction experiment. The developed spectrometer was used for spectroscopy of bremsstrahlung X-rays generated by intense laser-plasma interactions using a 200 μm thickness SiO2 converter. The X-ray spectrum obtained with the Compton X-ray spectrometer is consistent with that obtained with a DET X-ray spectrometer, furthermore higher certainly of a spectral intensity is obtained with the Compton X-ray spectrometer than that with the DET X-ray spectrometer in the photon energy range above 5 MeV.

Irradiating a metal wire with an intense femtosecond laser pulse induces a terahertz (THz) surface wave that travels along the wire. Here, the characteristics of the THz surface wave generated by the laser–wire interaction are investigated in detail by using an electro-optical method to determine the dependence of surface wave properties on laser energy and wire diameter. The surface wave is distributed by the Hankel function in the wire radial direction. On the wire surface, the electric field is estimated to be MV/cm. The peak electric field of the surface wave and the conversion efficiency from laser energy to surface wave energy are found to be proportional to the laser energy raised to the power of 0.67 and 0.3, respectively.

This paper reports an experimental investigation of a scheme to produce an intense, pulsed, point-like, and quasi-monoenergy neutron source. In this scheme, the inner wall of a deuterated plastic spherical cavity is mono-directionally irradiated by a 2.4 kJ laser beam through an open-tip gold cone inserted into the cavity. The whole inner wall of the cavity is illuminated by laser light owing to multiple laser reflections, and the laser-ablated plasma stagnates near the center of the cavity, at which a several keV hot spot is generated. Thermonuclear and beam D-D fusion reactions occur in the hot spot. We have demonstrated the neutron yield exceeding 107 neutrons per pulse from a

Quasi-static magnetic-fields up to $800\,$T are generated in the interaction of intense laser pulses ($500\,$J, $1\,$ns, $10^{17}\,$W/cm$^2$) with capacitor-coil targets of different materials. The reproducible magnetic-field peak and rise-time, consistent with the laser pulse duration, were accurately inferred from measurements with GHz-bandwidth inductor pickup coils (B-dot probes). Results from Faraday rotation of polarized optical laser light and deflectometry of energetic proton beams are consistent with the B-dot probe measurements at the early stages of the target charging, up to $t\approx 0.35\,$ns, and then are disturbed by radiation and plasma effects. The field has a dipole-like distribution over a characteristic volume of $1\,$mm$^3$, which is coherent with theoretical expectations. These results demonstrate a very efficient conversion of the laser energy into magnetic fields, thus establishing a robust laser-driven platform for reproducible, well characterized, generation of quasi-static magnetic fields at the kT-level, as well as for magnetization and accurate probing of high-energy-density samples driven by secondary powerful laser or particle beams., 16 pages, 7 figures

A series of experiments were carried out to evaluate the energy-coupling efficiency from heating laser to a fuel core in the fast-ignition scheme of laser-driven inertial confinement fusion. Although the efficiency is determined by a wide variety of complex physics, from intense laser plasma interactions to the properties of high-energy density plasmas and the transport of relativistic electron beams (REB), here we simplify the physics by breaking down the efficiency into three measurable parameters: (i) energy conversion ratio from laser to REB, (ii) probability of collision between the REB and the fusion fuel core, and (iii) fraction of energy deposited in the fuel core from the REB. These three parameters were measured with the newly developed experimental platform designed for mimicking the plasma conditions of a realistic integrated fast-ignition experiment. The experimental results indicate that the high-energy tail of REB must be suppressed to heat the fuel core efficiently.

In this work we report the successful implementation of plasma mirror (PM) technology on an LFEX laser facility at the Institute of Laser Engineering, Osaka University. The LFEX laser pulse was successfully refocused at the target chamber center (TCC) by means of a spherical plasma mirror, resulting in 5 × 1018 W cm−2 laser intensity, with 45% reflectivity at a laser flux of about 90 J cm−2 on the PM. Experimental results show stable focusing and pointing of the LFEX pulse after PM refocusing. The contrast improvement was demonstrated by both cooler fast electron slope temperature distribution as well as by the ability to shoot sub-µm plastic foils obtaining proton beams with maximum energy exceeding 20 MeV. Experimental results are qualitatively reproduced by 2D particle in cell simulations.

The study of fast electron spectrum optimization by suppression of preformed plasma in fast ignition targets is presented in this work. Integrated fast-electron spectra for electron energies below 3 MeV—the energy range responsible for core heating—are compared for different preformed plasma conditions. The pulse contrast (the ratio of peak-to-pedestal laser intensities) is compared for 108, 109 and 1011 conditions at constant laser energy (~500 J), pulse duration (2 ps), spot size (30% encircled energy on 50 µm diameter) and laser intensity (around 1 × 1019 W cm−2). The best electron spectrum optimization, consisting of maximized electron number for energies below 3 MeV was obtained with 14 µm thick cone targets. The energy coupling efficiency from heating laser to core plasma, assuming typical core plasma parameters, was estimated to be 2%, although 0.37% was obtained with previous conditions with poor pulse contrast and a 7 µm thick cone target.

A photonuclear-reaction-based hard x-ray spectrometer is developed to measure the number and energy spectrum of fast electrons generated by interactions between plasma and intense laser light. In this spectrometer, x-rays are converted to neutrons through photonuclear reactions, and the neutrons are counted with a bubble detector that is insensitive to x-rays. The spectrometer consists of a bundle of hard x-ray detectors that respond to different photon-energy ranges. Proof-of-principle experiment was performed on a linear accelerator facility. A quasi-monoenergetic electron bunch (Ne = 1.0 × 10(-6) C, Ee = 16 ± 0.32 MeV) was injected into a 5-mm-thick lead plate. Bremsstrahlung x-rays, which emanate from the lead plate, were measured with the spectrometer. The measured spectral shape and intensity agree fairly well with those computed with a Monte Carlo simulation code. The result shows that high-energy x-rays can be measured absolutely with a photon-counting accuracy of 50%-70% in the energy range from 2 MeV to 20 MeV with a spectral resolution (Δhν/hν) of about 15%. Quantum efficiency of this spectrometer was designed to be 10(-7), 10(-4), 10(-5), respectively, for 2-10, 11-15, and 15-25 MeV of photon energy ranges.

A universal procedure was developed to calibrate image plate scanners using radioisotope sources. Techniques to calibrate scanners and sources, as well as cross-calibrate scanner models, are described to convert image plate dosage into physical units. This allows for the direct comparison of quantitative data between any facility and scanner. An empirical relation was also derived to establish sensitivity response settings for arbitrary gain settings. In practice, these methods may be extended to any image plate scanning system.

The characteristics of oxygen-enriched liquid scintillators with very low afterglow are investigated and optimized for application to a single-hit neutron spectrometer for fast ignition experiments. It is found that 1,2,4-trimethylbenzene has better characteristics as a liquid scintillator solvent than the conventional solvent, p-xylene. In addition, a benzophenon-doped BBQ liquid scintillator is shown to demonstrate very rapid time response, and therefore has potential for further use in neutron diagnostics with fast time resolution.

This article documents the addition of 142 microsatellite marker loci to the Molecular Ecology Resources database. Loci were developed for the following species: Agriophyllum squarrosum, Amazilia cyanocephala, Batillaria attramentaria, Fungal strain CTeY1 (Ascomycota), Gadopsis marmoratus, Juniperus phoenicea subsp. turbinata, Liriomyza sativae, Lupinus polyphyllus, Metschnikowia reukaufii, Puccinia striiformis and Xylocopa grisescens. These loci were cross-tested on the following species: Amazilia beryllina, Amazilia candida, Amazilia rutila, Amazilia tzacatl, Amazilia violiceps, Amazilia yucatanensis, Campylopterus curvipennis, Cynanthus sordidus, Hylocharis leucotis, Juniperus brevifolia, Juniperus cedrus, Juniperus osteosperma, Juniperus oxycedrus, Juniperus thurifera, Liriomyza bryoniae, Liriomyza chinensis, Liriomyza huidobrensis and Liriomyza trifolii. © 2013 John Wiley & Sons Ltd.

Laser pulse contrast exceeding 1011 was demonstrated on a kilojoule-class petawatt laser for fast ignition experiments (LFEX) laser system [J. Phys. IV France133, 81 (2006)10.1051/jp4:2006133016] by implementing a 2 in. plasma mirror. Laser beams of up to 1.2 kJ striking the plasma mirror with a pulse duration of 1.5 ps were reflected and focused onto a target without significant distortions in the focal spot. Transmitted light from the plasma mirror reveals that it has a high reflectivity 2 ps before the main peak. The estimated laser pulse contrast at the target was 1011 at 1 ns before the main peak. No preformed plasma was observed with an optical interferometry diagnostics, but in the experiment without a plasma mirror a preplasma was clearly observed. The energetic proton was generated from a 0.1 μm thick CH film showing excellent pulse contrast. This technique constitutes a promising method to enhance the LFEX laser system performance in fast ignition experiments.

The dependence of high-energy electron generation on the pulse duration of a high intensity LFEX laser was experimentally investigated. The LFEX laser (λ = 1.054 and intensity = 2.5 – 3 x 1018 W/cm2) pulses were focused on a 1 mm3 gold cubic block after reducing the intensities of the foot pulse and pedestal by using a plasma mirror. The full width at half maximum (FWHM) duration of the intense laser pulse could be set to either 1.2 ps or 4 ps by temporally stacking four beams of the LFEX laser, for which the slope temperature of the high-energy electron distribution was 0.7 MeV and 1.4 MeV, respectively. The slope temperature increment cannot be explained without considering pulse duration effects on fast electron generation.

Hot electrons which are generated from targets irradiated by a high-intense laser are measured by two electron spectrometers (ESMs). However, total electron energy observed by the ESM is only less than 1%. Hot electrons are confined by self-fields due to the huge current. When an external magnetic field of several hundred Tesla is applied during the laser irradiation on targets, the ESM signals always increase. In the simulation, the same result can be obtained. The reason is that the Alfven limit can be mitigated due to the external longitudinal magnetic field.

A petawatt laser for fast ignition experiments (LFEX) laser system [N. Miyanaga et al., J. Phys. IV France 133, 81 (2006)], which is currently capable of delivering 2 kJ in a 1.5 ps pulse using 4 laser beams, has been constructed beside the GEKKO-XII laser facility for demonstrating efficient fast heating of a dense plasma up to the ignition temperature under the auspices of the Fast Ignition Realization EXperiment (FIREX) project [H. Azechi et al., Nucl. Fusion 49, 104024 (2009)]. In the FIREX experiment, a cone is attached to a spherical target containing a fuel to prevent a corona plasma from entering the path of the intense heating LFEX laser beams. The LFEX laser beams are focused at the tip of the cone to generate a relativistic electron beam (REB), which heats a dense fuel core generated by compression of a spherical deuterized plastic target induced by the GEKKO-XII laser beams. Recent studies indicate that the current heating efficiency is only 0.4%, and three requirements to achieve higher efficiency of the fast ignition (FI) scheme with the current GEKKO and LFEX systems have been identified: (i) reduction of the high energy tail of the REB; (ii) formation of a fuel core with high areal density using a limited number (twelve) of GEKKO-XII laser beams as well as a limited energy (4 kJ of 0.53-μm light in a 1.3 ns pulse); (iii) guiding and focusing of the REB to the fuel core. Laser–plasma interactions in a long-scale plasma generate electrons that are too energetic to efficiently heat the fuel core. Three actions were taken to meet the first requirement. First, the intensity contrast of the foot pulses to the main pulses of the LFEX was improved to >109. Second, a 5.5-mm-long cone was introduced to reduce pre-heating of the inner cone wall caused by illumination of the unconverted 1.053-μm light of implosion beam (GEKKO-XII). Third, the outside of the cone wall was coated with a 40-μm plastic layer to protect it from the pressure caused by imploding plasma. Following the above improvements, conversion of 13% of the LFEX laser energy to a low energy portion of the REB, whose slope temperature is 0.7 MeV, which is close to the ponderomotive scaling value, was achieved. To meet the second requirement, the compression of a solid spherical ball with a diameter of 200-μm to form a dense core with an areal density of ∼0.07 g/cm2 was induced by a laser-driven spherically converging shock wave. Converging shock compression is more hydrodynamically stable compared to shell implosion, while a hot spot cannot be generated with a solid ball target. Solid ball compression is preferable also for compressing an external magnetic field to collimate the REB to the fuel core, due to the relatively small magnetic Reynolds number of the shock compressed region. To meet the third requirement, we have generated a strong kilo-tesla magnetic field using a laser-driven capacitor-coil target. The strength and time history of the magnetic field were characterized with proton deflectometry and a B-dot probe. Guidance of the REB using a 0.6-kT field in a planar geometry has been demonstrated at the LULI 2000 laser facility. In a realistic FI scenario, a magnetic mirror is formed between the REB generation point and the fuel core. The effects of the strong magnetic field on not only REB transport but also plasma compression were studied using numerical simulations. According to the transport calculations, the heating efficiency can be improved from 0.4% to 4% by the GEKKO and LFEX laser system by meeting the three requirements described above. This efficiency is scalable to 10% of the heating efficiency by increasing the areal density of the fuel core.

The traditional fast ignition scheme is that a compressed core created by an imploding laser is auxiliary heated and ignited by the hot electrons (produced by a short pulse laser guided through the cone and guided under-dense plasma). However sufficient heating has not be achieved because the hot electron energy is too high and dissipated in the cone, the angular divergence of the hot electron is too large, and the distance from the generation point to the core is too long. Here we clarify the problems of fast ignition by observation of the hot-electron spectra.

The energy coupling efficiency (CE) in Fast Ignition (FI) laser fusion was studied at GEKKO XII and LFEx laser facility by using newly developed targets and plasma diagnostic instruments. The gated-liquid scintillator neutron detectors had been upgraded by using neutron collimators for intense background fluxes of γ-rays and neutrons in the FI experiment. Clear fusion neutron signal was successfully recorded in the sub-kJ heating FI experiment. Up to 5 times neutron yield enhancement was observed, and the CE of the heating laser to core plasma was estimated to be 1.6% for cone-in-shell target implosion by 9 beams and core heating by LFEX pulse 115 ps before bang time. The laser-to-electron energy conversion efficiency was separately diagnosed using a newly developed target and resulted to be 45%. The fast electron energy spectrum was estimated to be 2.3 MeV slope temperature by hard x-ray spectroscopy. Monte Carlo simulations demonstrate the consistency of the data set.