Time Of Shock Breakout Research Articles

Extensive characterization of Marshak waves observed at the LIL laser facility

We detail results of an experiment performed at the Ligne d'Intégration Laser facility aimed at studying supersonic and diffusive radiation front propagation in low-density SiO2 aerogel (20 and 40 mg/cm3) enclosed in a gold tube, driven by thermal emission from a laser-heated spherical gold cavity. The evolution of the front is studied continuously by measuring its self-emission with a 1D (one-dimensional) time-resolved soft x-ray imager. Measurement is performed along (through a 200-μm-wide observation slit) and at the exit of the tube giving access to the dynamics and the curvature of the front. Experimental results are then compared successfully to results from the 3D (three-dimensional) radiation hydrodynamics code TROLL, which shows that if continuous tracking of the front position is accessible with this experimental scheme, measurement of its maximum radiation temperature is on the contrary affected by radiation closure of the observation slit. 3D simulations also indicate that this effect can even be worsened if one includes pointing errors of the x-ray imager. Radiation temperature along the tube was then inferred by combining results from the imager to a wall shock breakout time measurement using a velocity interferometer system for any reflector and results from a broadband x-ray spectrometer used to determine the temperature at the exit of the tube. A decrease in the radiation temperature along the tube is observed, the decrease being more important for the higher SiO2 aerogel density.

The laser shock station in the dynamic compression sector. I.

The Laser Shock Station in the Dynamic Compression Sector (DCS) [Advanced Photon Source (APS), Argonne National Laboratory] links a laser-driven shock compression platform with high energy x-ray pulses from the APS to achieve in situ, time-resolved x-ray measurements (diffraction and imaging) in materials subjected to well-characterized, high stress, short duration shock waves. This station and the other DCS experimental stations provide a unique and versatile facility to study condensed state phenomena subjected to shocks with a wide range of amplitudes (to above ∼350 GPa) and time-durations (∼10 ns-1 µs). The Laser Shock Station uses a 100 J, 5-17 ns, 351 nm frequency tripled Nd:glass laser with programmable pulse shaping and focal profile smoothing for maximum precision. The laser can operate once every 30 min. The interaction chamber has multiple diagnostic ports, a sample holder to expose 14 samples without breaking vacuum, can vary the angle between the x-ray and laser beams by 135°, and can translate to select one of the two types of x-ray beams. The x-ray measurement temporal resolution is ∼90 ps. The system is capable of reproducible, well-characterized experiments. In a series of 10 shots, the absolute variation in shock breakout times was less than 500 ps. The variation in peak particle velocity at the sample/window interface was 4.3%. This paper describes the entire DCS Laser Shock Station, including sample fabrication and diagnostics, as well as experimental results from shock compressed tantalum that demonstrate the facility's capability for acquiring high quality x-ray diffraction data.

Aspherical Supernovae: Effects on Early Light Curves

Abstract Early light from core-collapse supernovae, now detectable in high-cadence surveys, holds clues to a star and its environment just before it explodes. However, effects that alter the early light have not been fully explored. We highlight the possibility of nonradial flows at the time of shock breakout. These develop in sufficiently nonspherical explosions if the progenitor is not too diffuse. When they do develop, nonradial flows limit ejecta speeds and cause ejecta–ejecta collisions. We explore these phenomena and their observational implications using global, axisymmetric, nonrelativistic FLASH simulations of simplified polytropic progenitors, which we scale to representative stars. We develop a method to track photon production within the ejecta, enabling us to estimate band-dependent light curves from adiabatic simulations. Immediate breakout emission becomes hidden as an oblique flow develops. Nonspherical effects lead the shock-heated ejecta to release a more constant luminosity at a higher, evolving color temperature at early times, effectively mixing breakout light with the early light curve. Collisions between nonradial ejecta thermalize a small fraction of the explosion energy; we will address emission from these collisions in a subsequent paper.

MAGNETAR-DRIVEN SHOCK BREAKOUT AND DOUBLE-PEAKED SUPERNOVA LIGHT CURVES

ABSTRACT The light curves of some luminous supernovae are suspected to be powered by the spindown energy of a rapidly rotating magnetar. Here we describe a possible signature of the central engine: a burst of shock breakout emission occurring several days after the supernova explosion. The energy input from the magnetar inflates a high-pressure bubble that drives a shock through the pre-exploded supernova ejecta. If the magnetar is powerful enough, that shock will near the ejecta surface and become radiative. At the time of shock breakout, the ejecta will have expanded to a large radius ( ∼ 10 14 cm) so that the radiation released is at optical/ultraviolet wavelengths ( T eff ≈ 20,000 K) and lasts for several days. The luminosity and timescale of this magnetar-driven shock breakout are similar to the first peak observed recently in the double-peaked light curve of SN-LSQ14BDQ. However, for a large region of model parameter space, the breakout emission is predicted to be dimmer than the diffusive luminosity from direct magnetar heating. A distinct double-peaked light curve may therefore only be conspicuous if thermal heating from the magnetar is suppressed at early times. We describe how such a delay in heating may naturally result from inefficient dissipation and thermalization of the pulsar wind magnetic energy. Without such suppression, the breakout may only be noticeable as a small bump or kink in the early luminosity or color evolution, or as a small but abrupt rise in the photospheric velocity. A similar breakout signature may accompany other central engines in supernovae, such as a black hole accreting fallback material.

Recent results from experimental studies on laser–plasma coupling in a shock ignition relevant regime

Shock ignition (SI) is an appealing approach in the inertial confinement scenario for the ignition and burn of a pre-compressed fusion pellet. In this scheme, a strong converging shock is launched by laser irradiation at an intensity Iλ2 > 1015 W cm−2 µm2 at the end of the compression phase. In this intensity regime, laser–plasma interactions are characterized by the onset of a variety of instabilities, including stimulated Raman scattering, Brillouin scattering and the two plasmon decay, accompanied by the generation of a population of fast electrons. The effect of the fast electrons on the efficiency of the shock wave production is investigated in a series of dedicated experiments at the Prague Asterix Laser Facility (PALS).We study the laser–plasma coupling in a SI relevant regime in a planar geometry by creating an extended preformed plasma with a laser beam at ∼7 × 1013 W cm−2 (250 ps, 1315 nm). A strong shock is launched by irradiation with a second laser beam at intensities in the range 1015–1016 W cm−2 (250 ps, 438 nm) at various delays with respect to the first beam. The pre-plasma is characterized using x-ray spectroscopy, ion diagnostics and interferometry. Spectroscopy and calorimetry of the backscattered radiation is performed in the spectral range 250–850 nm, including (3/2)ω, ω and ω/2 emission. The fast electron production is characterized through spectroscopy and imaging of the Kα emission. Information on the shock pressure is obtained using shock breakout chronometry and measurements of the craters produced by the shock in a massive target.Preliminary results show that the backscattered energy is in the range 3–15%, mainly due to backscattered light at the laser wavelength (438 nm), which increases with increasing the delay between the two laser beams. The values of the peak shock pressures inferred from the shock breakout times are lower than expected from 2D numerical simulations. The same simulations reveal that the 2D effects play a major role in these experiments, with the laser spot size comparable with the distance between critical and ablation layers.

Advances in the investigation of shock-induced reflectivity of porous carbon

AbstractWe studied the behavior of porous carbon compressed by laser-generated shock waves. In particular, we developed a new design for targets, optimized for the investigation of carbon reflectivity at hundred-GPa pressures and eV/k temperatures. Specially designed “two-layer-two materials” targets, comprising porous carbon on transparent substrates, allowed the probing of carbon reflectivity and a quite accurate determination of the position in the P, T plane. This was achieved by the simultaneous measurement of shock breakout times, sample temperature (by optical pyrometry) and uid velocity. The experiments proved the new scheme is reliable and appropriate for reflectivity measurements of thermodynamical states lying out of the standard graphite or diamond hugoniot. An increase of reflectivity in carbon has been observed at 260 GPa and 14,000 K while no increase in reflectivity is found at 200 GPa and 20,000 K. We also discuss the role of numerical simulations in the optimization of target parameters and in clarifying shock dynamics.

Initial conditions of radiative shock experiments

We performed experiments at the Omega Laser Facility to characterize the initial, laser-driven state of a radiative shock experiment. These experiments aimed to measure the shock breakout time from a thin, laser-irradiated Be disk. The data are then used to inform a range of valid model parameters, such as electron flux limiter and polytropic γ, used when simulating radiative shock experiments using radiation hydrodynamics codes. The characterization experiment and the radiative shock experiment use a laser irradiance of ∼7 × 1014 W cm−2 to launch a shock in the Be disk. A velocity interferometer and a streaked optical pyrometer were used to infer the amount of time for the shock to move through the Be disk. The experimental results were compared with simulation results from the Hyades code, which can be used to model the initial conditions of a radiative shock system using the CRASH code.

Probing Shock Breakout with Serendipitous GALEX Detections of Two SNLS Type II-P Supernovae

We report the serendipitous detection by GALEX of fast (<1 day) rising (≳1 mag) UV emission from two Type II plateau (II-P) supernovae (SNe) at z = 0.185 and 0.324 discovered by the Supernova Legacy Survey. Optical photometry and VLT spectroscopy 2 weeks after the GALEX detections link the onset of UV emission to the time of shock breakout. Using radiation hydrodynamics and non-LTE radiative transfer simulations, and starting from a standard red supergiant (RSG; Type II-P SN progenitor) star evolved self-consistently from the main sequence to iron core collapse, we model the shock breakout phase and the 55 hr that follow. The small scale height of our RSG atmosphere model suggests that the breakout signature is a thermal soft X-ray burst (λpeak ~ 90 A) with a peak duration of ≾2000 s. Longer durations are possible but require either an extended and tenuous nonstandard envelope or an unusually dense RSG wind with M ~ 10^(-3)M_☉yr^(-1). The GALEX observations miss the peak of the luminous (M_(FUV)≈ − 20), UV burst but unambiguously capture the rise of the emission and a subsequent 2 day long plateau. The postbreakout, UV-bright plateau is a prediction of our model in which the shift of the peak of the spectral energy distribution (SED) from ∼100 to ∼1000 A and the ejecta expansion both counteract the decrease in bolometric luminosity from ∼10^(11) to ~ 10^9 L_☉ over that period. Based on the observed detection efficiency of our study, we make predictions for the breakout detection rate of the GALEX Time Domain Survey.

Line-imaging velocimeter for shock diagnostics at the OMEGA laser facility

A line-imaging velocity interferometer has been implemented at the OMEGA laser facility of the Laboratory for Laser Energetics, University of Rochester. This instrument is the primary diagnostic for a variety of experiments involving laser-driven shock-wave propagation, including high-pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh–Taylor experiments, and shock timing experiments for inertial confinement fusion research. Using a laser probe beam to illuminate a target, the instrument measures shock breakout times at temporal resolutions as low as 20 ps, and spatial resolution ∼4 μm. For velocity measurements the detection limit is &amp;lt;0.1 km/s, and velocities of interfaces, free surfaces, and shock fronts traveling through transparent media can be measured with accuracies ∼1% over the range from 4 km/s to greater than 50 km/s. Quantitative measurements of the optical reflectance of ionizing shock fronts can also be obtained simultaneously with the velocity measurements.

Experimental studies of laser–target interactions in an ambient gas, under IFE conditions

Studies of reactor designs for inertial fusion energy (IFE) have indicated that some of the material requirements can be alleviated if the target chamber is filled with a low-pressure inert gas (<1 Torr). The experiments described in this paper examine the effects of such an ambient gas on the laser-target interactions relevant to laser-driven IFE. These experiments used the Nike KrF laser facility at the Naval Research Laboratory to irradiate uncoated 78 µm thick polystyrene (CH) foil targets at focal intensities around 1014 W cm−2. They compared the laser–target interactions in different inert gases (xenon, argon or krypton) at several ambient pressures up to 1 Torr with that of the vacuum (reference) case. The diagnostics included streaked rear-surface emission at wavelengths 460–540 nm and side-on shadowgraphy at 263 nm. The results of this study were encouraging. In spite of initial concerns about resonantly enhanced nonlinear optical effects in the Xe gas, we found no evidence of laser beam break-up, spreading, or attenuation. The shock breakout profiles (from emitted light) and the front and rear surface plasma profiles (from shadowgraphy) remained smooth and symmetric in all cases. The central shock breakout times, and thus the central laser irradiances, were about the same for the target in an inert gas as in vacuum. Our analysis indicates that the large nonlinear optical processes in atomic Xe are self-limiting because the converging beam ionizes the gas, thereby removing the atoms from the most intense part.

Real temperature calculation of shock wave driven by sub-nanosecond laser pulses

Time history of thermal band emission of a shock front, when breakout from aluminium target into vacuum, has been calculated numerically. It is assumed that the shock is produced by irradiation of high intensity sub-nanosecond pulsed laser on the surface of aluminium planar targets in vacuum. The opacity of dense plasma at the shock front and in the vacuum–aluminium interface, and its effects on thermal emissions was considered in these calculations. Using the results of an experiment that was recently reported and those of our model, the real temperature of the shock front was estimated. In that experiment simultaneous measurements of the colour temperature of dense plasma in a shock front, and the shock velocity at the time of shock breakout from the aluminium targets into the vacuum were reported for the study of the equation of state (EOS). The results of the model show a good agreement with the SESAME library EOS.

Young Circumstellar Disks near Evolved Massive Stars and Supernovae

There is increasing evidence that low-mass stars with circumstellar disks can be born close to massive stars, in some cases within tenths of a parsec. If the disks have lifetimes greater than those of the more massive stars, they are exposed to radiation fields and gas flows from the late evolutionary phases and supernovae of the massive stars. The fast flows from supernovae are likely to give some stripping of mass from the disks but do not typically lead to complete disruption of the disks. In the slow wind from a red supergiant star, there is the possibility of gravitational accretion of wind matter onto the circumstellar disk. In the supernova explosion of a red supergiant, the radiative flux at the time of shock breakout can heat and ionize a nearby disk, leading to transient, narrow-line emission. There are consequences for the solar nebula if it was born ~0.2 pc from a massive star that became a red supergiant. Accretion from the wind could supply a substantial amount of 26Al to the disk. The high radiative luminosity of the eventual supernova could lead to the melting of dust grains and the formation of chondrules. The passage of the supernova ejecta could drive a shock wave in the disk, heating it.

High-energy Emission from Supernovae and Remnants

An early burst of energetic radiation is expected from a supernova at the time of shock breakout. This emission has not been directly observed but has been inferred from the photoionization around SN 1987A. X-ray emission has been detected from core-collapse supernovae in the days to years after the explosion as they interact with their circumstellar winds. Young Galactic supernova remnants provide the possibility of determining the composition structure of the ejecta through X-ray spectroscopy. An exciting finding for older remnants is that a number of remnants that appear to be interacting with molecular gas may be sources of high-energy γ-ray emission. The clumpy structure of molecular clouds has implications for the structure expected in high-energy emission. Finally, the field of γ-ray-line spectroscopy is beginning to yield results relevant to the explosive nucleosynthesis of radionuclides in supernovae.