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The nuclear burn history provides critical information about the dynamics of the hot-spot formation and high-density fuel-shell assembly of an Inertial Confinement Fusion (ICF) implosion, as well as information on the impact of alpha heating, and a multitude of implosion failure mechanisms. Having this information is critical for assessing the energy-confinement time τE and performance of an implosion. As the confinement time of an ICF implosion is a few tens of picoseconds, less than 10-ps time resolution is required for an accurate measurement of the nuclear burn history. In this study, we propose a novel 1-ps time-resolution detection scheme based on the Pockels effect. In particular, a conceptual design for the experiment on the National Ignition Facility and OMEGA are elaborated upon herein. A small organic Pockels crystal "DAST" is designed to be positioned ∼5 mm from the ICF implosion, which is scanned by a chirped pulse generated by a femto-second laser transmitted through a polarization-maintained optical fiber. The originally linearly polarized laser is changed to an elliptically polarized laser by the Pockels crystal when exposed to neutrons, and the modulation of the polarization will be analyzed. Our study using 35-MeV electrons showed that the system impulse response is 0.6 ps. The response time is orders of magnitude shorter than current systems. Through measurements of the nuclear burn history with unprecedented time resolution, this system will help for a better understanding of the dynamics of the hot-spot formation, high-density fuel-shell assembly, and the physics of thermonuclear burn wave propagation. [ABSTRACT FROM AUTHOR]

Foot and pedestal pulses that precede the main pulse from a high-intensity laser greatly affect laser-plasma interactions. Especially in fast ignition schemes, preceding pulses generate a plasma prior to irradiation by the main pulse. This results in a too energetic and divergent electron beam being generated in the preformed plasma, which reduces the energy coupling efficiency from the heating laser to the dense fuel core. A preformed plasma with a density scale length of 40-60 μm was observed by a time- and space-resolved x-ray backlight technique using the LFEX laser system at the Institute of Laser Engineering, Osaka University. Preceding pulses (i.e., the foot and pedestal) of the LFEX were characterized by comparing observations with calculations results obtained using a two-dimension (2D) radiation-hydrodynamic simulation code. In a separate experiment, the 2D code was benchmarked with the experimentally observed hydrodynamic behavior of a gold plasma produced by a nanosecond laser pulse that mimicked foot and pedestal pulses (intensity: 1 ×1011-1×1012W/cm2). The preceding pulses were estimated to have an intensity of 1 ×1012-1013W/cm2, a duration of 2.0 ns, and a spot diameter at the target of 200-600 μm by comparing the measured hydrodynamics of the preformed plasma with that calculated by the 2D hydrodynamic simulation code. [ABSTRACT FROM AUTHOR]

Strong magnetic fields from a few hundred to a thousand tesla have been produced in a laboratory by using high-intensity laser beams. This strong magnetic field in a laboratory becomes a powerful tool to perform experiments in the fields such as laboratory astrophysics and nuclear fusion research. The diffusion dynamics of a pulsed magnetic field in a target is a key phenomenon for experiments with the laser-produced magnetic field. Here, we have developed a two-dimensional (2D) electromagnetic dynamics simulation code with consideration of inductive heating to simulate spatiotemporally resolved 2D profiles of the applied magnetic field in a target. The application of an external kilo-tesla-level magnetic field to a gold-cone-attached target is a promising scheme for the enhancement of heating efficiency of the fast-ignition inertial confinement fusion scheme. Our simulation revealed that the magnetic field heats the gold cone due to the inductive heating and penetrates the gold cone during its pulse duration. The developed simulation code is generally useful for designing and analyzing experiments using a strong magnetic field. [ABSTRACT FROM AUTHOR]

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 (>1013 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. [ABSTRACT FROM AUTHOR]

We captured single shot images of ZnO emission patterns originating from excitation with the EUV laser at Japan Atomic Energy Agency (JAEA). The EUV laser was focused to a spot size of 1~\mu \m on the ZnO crystal by a Fresnel Zone Plate (FZP). The FZP was shifted along the propagation direction of the EUV beam, essentially changing the spot size at the ZnO surface. The emission pattern was detected by a magnifier. The waist radii were determined from the fitting curve as 5.0~\mu \m along the horizontal axis and 4.7~\mu \m along the vertical axis. We also evaluated the spatial resolution of the magnifier, which consists of a Schwarzschild mirror, two lenses and a camera lens to be about 4~\mu \m. These results suggest that the ZnO crystal has sub-micron spatial resolution when used as an in-situ imaging device for the diagnostics of EUV/X-ray sources. [ABSTRACT FROM PUBLISHER]

Scintillation properties of Ce^3+-doped 20Al(PO3)3- 80LiF glasses were investigated in order to seek a candidate for down-scattered neutron scintillator in nuclear fusion diagnostics. The decay constant of \ APLF80 + 3Ce with 5.5 MeV alpha particles from ^241Am radioisotope excitation was measured to be 32.1 ns. Moreover, sufficiently low afterglow decay profile and improved light output of \ APLF80 + 3Ce were experimentally demonstrated. [ABSTRACT FROM PUBLISHER]

We show that a hydrothermal method-grown ZnO is a potential material of an imaging device for soft X-ray laser diagnostics. The beam profile of a soft X-ray laser was evaluated by characterizing the exciton emission patterns of ZnO. The single shot image of emission patterns is clear enough to monitor the evolution of the beam radius around the focal point. By plotting the emission pattern radii at each position, the beam profile of the Ni-like Ag ion plasma laser was estimated from the waist radii as 29 \mum and 21 \mum in the horizontal and vertical axis, respectively. The divergence angle was estimated to be around 7.2 mrad and 11 mrad in the horizontal and vertical axis, respectively. The beam quality evaluated from the M^2 factor was 47 along the horizontal axis and 50 along the vertical axis. Spatial resolution of the magnifier was estimated to be 6 \mum and is expected to improve by optimizing the optics of the magnifier and using a telescope. Our results would enhance the use of ZnO as a high-spatial resolution in-situ imaging device that would play a crucial role in the development and application of soft X-ray light sources. [ABSTRACT FROM PUBLISHER]

Scintillation properties of Pr3+-doped 20Al(PO3)3-80 LiF glasses melted in N2 were investigated to seek a candidate for a scattered neutron scintillator in nuclear fusion diagnostics. The fluorescence lifetime of the sample with 217 nm ultraviolet femtosecond pulse excitation was measured to be 19.5 ns. More importantly, the fluorescence lifetime with alpha particles from 241Am radioisotope excitation was determined to be 6.7 ns. Based on our material design strategy, we have successfully developed the fast response time praseodymium-doped 6Li glass scintillator for scattered neutron diagnostics. [ABSTRACT FROM AUTHOR]

Experimental results are presented on the neutron scintillating properties of a custom-designed Pr3+(praseodymium)-doped lithium (Li) glass. Luminescence was observed at 278 nm wavelength, originating from the 5d-4f transition. Time-resolved measurements yielded about 20 ns decay times for ultraviolet and x-ray excitation while much faster decay times of about 6 ns were observed for alpha particle and neutron excitation. Actual time-of-flight data in laser fusion experiments at the GEKKO XII facility of the Institute of Laser Engineering, Osaka University reveal that it can clearly discriminate fusion neutrons from the much stronger x-rays signals. This material can promise improved accuracy in future scattered neutron diagnostics. [ABSTRACT FROM AUTHOR]

Recently one-dimensional and multichannels multi-imaging x-ray streak camera (1D+McMIXS) has been proposed as an ultrafast diagnostic tool for imploded core plasma of shell-cone target. This diagnostic system can provide much more information of core plasma dynamics, such as the shell trajectory before the maximum compression, two dimensional (2D) x-ray images, and 2D map of electron temperature. The 1D+McMIXS was used in an implosion experiment of a shell target with a cone for fast ignition at Gekko XII laser facility. The interaction between the core plasma and the tip of the cone was observed and revealed some detailed structures. A series of time-resolved 2D x-ray images were reconstructed and a nominal temperature evolution was also mapped. [ABSTRACT FROM AUTHOR]

Suppression of hydrodynamic instabilities is very crucial for the ultimate goal of inertial fusion energy (IFE). A high-Z doped plastic of CHBr (brominated polystyrene) ablator is a very promising candidate to suppress the ablative Rayleigh-Taylor (RT) instability in a directly laser-driven IFE target. When a CHBr target is irradiated by intense laser beams, bromine atoms in the corona plasma emit strong radiation. The strong radiation drives the radiative ablation front inside the CHBr targets. This radiative ablation in the high-Z doped plastic target has many advantages for the suppression of the growth of the RT instability in analogy to the indirect-drive approach, i.e., large mass ablation rate, long density scale length and low peak density. Two-dimensional (2D) hydrodynamic simulation shows significant suppression of the RT instability in a CHBr target compared to an undoped polystyrene (CH) target. RT growth rate, calculated theoretically using the Betti-Goncharov procedure with a one-dimensional radiation-hydrodynamic simulation code, is in good agreement with the 2D calculations. Experiments were performed at the GEKKO XII- [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] HIPER (High Intensity Plasma Experimental Research) laser facility. The trajectory of a laser-driven CHBr target observed in the experiment was reproduced fairly well by the simulation. The radiative ablation front formed inside a directly laser-driven CHBr target was clearly observed for the first time. The strong suppression of the RT instability in the CHBr target was confirmed using the face-on and side-on x-ray backlighting technique. The high-Z doped ablator can be applied to high density cryogenic deuterium-deuterium and deuterium-tritium compression, because the hydrogen-isotopes are nearly transparent to x rays, which are transmitted through the ablator from the laser-irradiation side. [ABSTRACT FROM AUTHOR]

The temporal evolution of the density profile of a directly laser-driven polystyrene target was observed for the first time using an x-ray penumbral imaging technique coupled with side-on x-ray backlighting at the GEKKO XII [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)]–High Intensity Plasma Experimental Research laser facility (I[sub L]=0.7×10[sup 14] W/cm[sup 2], λ[sub L]=0.35 μm). This density measurement makes it possible to experimentally confirm all physical parameters [γ(k),k,g,m,ρ[sub a],L[sub m]] appearing in the modified Takabe formula for the growth rate of the ablative Rayleigh–Taylor instability. The measured density profiles were well reproduced by a one-dimensional hydrodynamic simulation code. The density measurement contributes toward fully understanding the ablative Rayleigh–Taylor instability. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Rayleigh-Taylor (RT) instability is one of the most important physical issues in the inertial confinement fusion research. The reduction of its growth rate due to laser-driven ablation, which is described by the modified Takabe formula, is of great importance for a precise understanding of the target physics. We have developed various diagnostic techniques for the measurement of the parameters appearing in the Takabe formula, such as the growth rate, the acceleration, the mass ablation rate, and the density structure including ablation density and density scalelength. Face-on and side-on x-ray backlighting were coupled with moire interferometry imaging, penumbral imaging, and Fresnel zoneplate imaging. All the physical parameters related to RT instability were measured experimentally, and compared with simulation results. [ABSTRACT FROM AUTHOR]

We developed and improved high space- and time-resolution x-ray imaging techniques (3-6 µm, 100-200 ps). These techniques were coupled with side-on x-ray backlighting for observing hydrodynamics of directly laser-driven polystyrene plasmas. As a high sensitive x-ray image detector, Imaging Plate was introduced to penumbral imaging technique [S. Fujioka et al., Rev. Sci. Instrum. 73, 2588 (2002)]. Noise in penumbral images was reduced by this improvement, and high quality density profiles of plasmas were obtained. A large-magnification slit camera, whose slit width and magnification were 4 µm and 82.8, was coupled with an x-ray streak camera (XSC). Due to the advantage of the large-magnification, high spatial resolution of 5.8 µm was found even with an XSC, the photocathode of which usually has low spatial resolution. These techniques are useful in understanding of hydrodynamic instability in inertial confinement fusion. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) penumbral imaging technique with high spatial resolution has been developed, and applied to density profile measurements in laser-driven Rayleigh-Taylor instability experiments at a GEKKO XII-HIPER laser system. A laser-irradiated planar target was observed with side-on x-ray backlighting. A penumbral image of an x-ray radiograph was made by using a knife-edge imager. The x-ray radiograph was, then, reconstructed by differentiating the penumbral image with a proper Wiener filtering. A density profile was deduced from the reconstructed x-ray radiograph. In a proof-of-principle experiment, the density profile of a polystyrene (PS) target before laser irradiation was measured by using this method, and high spatial resolution of 3-4 µm was demonstrated. A laser-irradiated PS target in the acceleration phase was observed. The experimentally observed density profile was found to be consistent with the prediction by a 1D hydrodynamic simulation code. The x-ray penumbral imaging is a very simple and useful technique with high spatial resolution for research in hydrodynamics relevant to inertial fusion energy. [ABSTRACT FROM AUTHOR]

Studies fundamental physics and implosion dynamics with the GEKKO XII glass laser system, by conducting a series of experiments using cryogenic deuterium targets. Measurement of the implosion dynamics of cryogenic deuterium foam with a plastic ablator and a CH shell with a controlled pressure of deuterium gas targets.

The characteristics of an APLF80+3Ce scintillator are presented. Its sufficiently fast decay profile, low afterglow, and an improved light output compared to the recently developed APLF80+3Pr, were experimentally demonstrated. This scintillator material holds promise for applications in neutron imaging diagnostics at the energy regions of 0.27 MeV of DD fusion down-scattered neutron peak at the world's largest inertial confinement fusion facilities such as the National Ignition Facility and the Laser Mégajoule. [ABSTRACT FROM AUTHOR]

Ultrafast, two-dimensional x-ray imaging is an important diagnostics for the inertial fusion energy research, especially in investigating implosion dynamics at the final stage of the fuel compression. Although x-ray radiography was applied to observing the implosion dynamics, intense x-rays emitted from the high temperature and dense fuel core itself are often superimposed on the radiograph. This problem can be solved by coupling the x-ray radiography with monochromatic x-ray imaging technique. In the experiment, 2.8 or 5.2 keV backlight x-rays emitted from laser-irradiated polyvinyl chloride or vanadium foils were selectively imaged by spherically bent quartz crystals with discriminating the out-of-band emission from the fuel core. This x-ray radiography system achieved 24 μm and 100 ps of spatial and temporal resolutions, respectively. [ABSTRACT FROM AUTHOR]

A simultaneous measurement of imploded core plasma and injection time of heating laser is conducted by using an x-ray framing camera (XFC). The experiments are performed using Gekko XII laser system for implosion of the deuterated polystyrene (CD) plastic shell target and Peta Watt (PW) laser system for heating. The time of PW laser injection is observed as the bright zone in the XFC image. The measured x-ray intensity profiles fit the Gaussian profiles well. The calculations of microchannel plate by using dynode model explain these broadened temporal profiles qualitatively. The peak position of fitted x-ray intensity profile is almost in agreement with the time when the high energy x ray is observed by x-ray streak camera. Moreover, the peak position is delayed corresponding to the delayed setting of PW laser injection time. From these results, it is concluded that we can estimate the heating laser injection time with resolution of the order of 10 ps by using XFC. [ABSTRACT FROM AUTHOR]

Ultrafast two-dimensional (2D) x-ray imaging is required to investigate the dynamics of fast-heated core plasma in inertial confinement fusion research. A novel x-ray imager, consisting of two toroidally bent Bragg crystals and an ultrafast 2D x-ray imaging camera, has been demonstrated. Sequential and 2D monochromatic x-ray images of laser-imploded core plasma were obtained with a temporal resolution of 20 ps, a spatial resolution of 31 μm, and a spectral resolution of over 200, simultaneously. [ABSTRACT FROM AUTHOR]

A shell target with a cone for guiding the heating beam has been proposed for the fast ignition scheme. Implosion of such target is no longer symmetric because of the cone. A fast two-dimensional x-ray imaging technique, two-dimensional (2D) sampling image x-ray streak camera was applied for the first time to observation of the dynamics of implosion and core plasma. X-ray emission image of the plasma was sampled with two-dimensionally distributed image sampling points, streaked with the tube, and the recorded signals were reconstructed as sequential 2D frame images. Shape and movement of the core plasma were clearly observed. [ABSTRACT FROM AUTHOR]

In study of hot and dense plasma, a high spatial resolution (a few microns) x-ray imaging is very important to observe these plasmas. The Fresnel phase zone plate (FPZP) consists of alternately material and transparent circular annuli placed concentrically, which image x rays using diffraction x rays from all annuli. FPZP have imaged 4.7–4.77 keV x rays with 2.2 μm spatial resolution. However FPZP has a problem that background level is comparable to signal level. In subtraction of background, the error of 10% is caused. For the accurate background subtraction, we designed new FPZP, which consist of three β layers of a transparent zone and two material zones. The new design FPZP parameters (thickness of material zones, each zone width) have been optimized, and in that optimum design signal-to-background ratio is 4 times better than conventional two layers FPZP. [ABSTRACT FROM AUTHOR]

Temporal resolved x-ray penumbral imaging has been developed using an image reconstruction procedure of the heuristic method and a wide dynamic range x-ray streak camera (XSC). Reconstruction procedure of the penumbral imaging is inherently intolerant to noise, a reconstructed image is strongly distorted by artifacts caused by noise in a penumbral image. Statistical fluctuation in the number of detected photon is the dominant source of noise in an x-ray image, however acceptable brightness of an image is limited by dynamic range of an XSC. The wide dynamic range XSC was used to obtain penumbral images bright enough to be reconstructed. Additionally, the heuristic method was introduced in the penumbral image reconstruction procedure. Distortion of reconstructed images is sufficiently suppressed by these improvements. Density profiles of laser driven brominated plastic and tin plasma were measured with this technique. [ABSTRACT FROM AUTHOR]

We investigate the photoluminescence (PL) and photoluminescence excitation (PLE) spectra of 20Al(PO3)3–80LiF+Pr glass (APLF+Pr) and Pr3+-doped LiCaAlF6 crystal (Pr:LiCAF) in order to determine the electronic states of Pr3+ in APLF glass host and to improve APLF+Pr scintillation properties. Ultraviolet (UV) emission bands at around 250 and 340 nm were observed from both materials and these can be ascribed to 4f5d→4f2 transitions in Pr3+. Emission at around 400 nm was also obtained and is principally attributed to 1S0→4f2 transition. Difference in the emission profiles of these two materials was found to be due to the extent of the 5d band and its position relative to the 1S0 state. Increasing the concentration of Pr3+ up to 2 mol % was found to improve UV emission ratio due to the faster cross-relaxation of 4f states. This could improve the quantum efficiency of APLF+Pr as a neutron scintillator for scattered-neutron diagnostics in laser fusion research. [ABSTRACT FROM AUTHOR]

We demonstrate the potential of a hydrothermal method-grown ZnO as a high-spatial resolution imaging device for in-situ soft X-ray laser diagnostics by characterizing the exciton emission patterns. By plotting the emission pattern radii at each position, we estimated the evolution of the beam radius around the focal point. The beam profile of the Ni-like Ag ion plasma laser was estimated from the waist radii as 29 and 21 µm, the divergence angle as 7.2 and 11 mrad and the M2 factor as 47 and 50 in the horizontal- and vertical-axis, respectively. Spatial resolution of the magnifier was estimated to be 6 µm and is expected to improve by optimizing the optics of the magnifier and using a telescope. Our results would enhance the use of ZnO as an imaging device that would play a crucial role in the development and application of soft X-ray light sources. [ABSTRACT FROM AUTHOR]

Ce:LuLiF4 is evaluated as a fast scintillator using a storage ring free-electron laser operating in the deep-ultraviolet region. The relatively flat spectral response across its absorption bands makes this material an attractive scintillator for various excitation sources. Its decay time is acceptable for ignition timing in fast-ignition, inertial confinement nuclear fusion using laser. This report is the first systematic study on Ce:LuLiF4 as a scintillator, wherein the storage ring free-electron laser is also shown as a powerful tool for material survey. [ABSTRACT FROM AUTHOR]

In this paper, we report on three-photon fluorescence and the possible observation of other complex optical processes in a ZnSe crystal for a kilojoule-class, 100 ps pulse, Nd:glass laser excitation. The emission properties of the ZnSe crystal and its excitation energy dependence were investigated under low and high-energy excitations. A 15 to 10 nm full width at half maximum (FWHM) spectral collapse, a 5 nm blue shift, and a shortened lifetime of fluorescence under high-energy excitation could indicate an amplified spontaneous emission. These findings present the feasibility of investigating the dynamics and spectral properties of three-photon fluorescence and other complex nonlinear optical processes in ZnSe at an extremely high excitation energy. [ABSTRACT FROM AUTHOR]