A two-dimensional theoretical model for the evolution of solid-density plasma irradiated by short, intense laser pulse is introduced. The electrons near the target surface are pushed inward by the radiation pressure, leading to a receding electron density jump where the laser is reflected. The electrostatic field of the resulting charge separation eventually balances the radiation pressure at the laser peak. After that the charge separation field becomes dominant. It accelerates and compresses the ions that are left behind until they merge with the compressed electrons, resulting in a high-density plasma peak. The laser pulse reflected from the receding electron density jump loses energy in plasma and suffers Doppler frequency red-shift, which can provide valuable information on the laser absorption rate and the speed of the receding electrons. Electron oscillations, including the u × B oscillations across the density jump at twice the laser frequency during the laser action, as well as the low-frequency oscillations appearing after laser action, are identified.

We present a novel method that we call FAINE, fast artificial intelligence neutron detection system. FAINE automatically classifies tracks of fast neutrons on CR-39 detectors using a deep learning model. This method was demonstrated using a LANDAUER Neutrak® fast neutron dosimetry system, which is installed in the External Dosimetry Laboratory (EDL) at Soreq Nuclear Research Center (SNRC). In modern fast neutron dosimetry systems, after the preliminary stages of etching and imaging of the CR-39 detectors, the third stage uses various types of computer vision systems combined with a manual revision to count the CR-39 tracks and then convert them to a dose in mSv units. Our method enhances these modern systems by introducing an innovative algorithm, which uses deep learning to classify all CR-39 tracks as either real neutron tracks or any other sign such as dirt, scratches, or even cleaning remainders. This new algorithm makes the third stage of manual CR-39 tracks revision superfluous and provides a completely repeatable and accurate way of measuring either neutrons flux or dose. The experimental results show a total accuracy rate of 96.7% for the true positive tracks and true negative tracks detected by our new algorithm against the current method, which uses computer vision followed by manual revision. This algorithm is now in the process of calibration for both alpha-particles detection and fast neutron spectrometry classification and is expected to be very useful in analyzing results of proton-boron11 fusion experiments. Being fully automatic, the new algorithm will enhance the quality assurance and effectiveness of external dosimetry, will lower the uncertainty for the reported dose measurements, and might also enable lowering the system’s detection threshold.

A new two-step approach for frequency conversion of laser radiation towards hard X-rays is developed and examined experimentally. Fast electrons are produced in a form of thin jets at the first stage, as an intense femtosecond laser pulses impinges on a micrometer water target. In the second stage the accelerated electrons hit a secondary metal target and generate characteristic K-shell radiation with a duration down to sub-femtosecond. It is shown that counter propagating laser radiation experiences very strong up-shift with up to 6 × 103 times of fundamental frequency by reflection from the electron jets.

The results on study of light sources based on spontaneous radiation of molecules KrCl* (λ ∼ 222 nm) and XeCl* (λ ∼ 308 nm) excited by a glow discharge are presented. It is demonstrated that additions of light inert gases (He and Ne) lead to increase in emission of radiation power and efficiency in mixtures Kr(Xe)-Cl2. A high-power cylindrical multi-section excilamp was built and energy, time, and spectrum characteristics have been studied. Average output power obtained in the UV spectral range were 1,9 kW at λ ∼ 222 nm and 1,1 kW at λ ∼ 308 nm with efficiencies with respect to the excitation power of up to 14%.

Spherical gold Hohlraums were heated by the iodine laser ASTERIX IV (200 J/0.4 ns at 440 nm) and were used to investigate radiative heating of low-Z plastic foils at temperatures up to 100 eV by time-resolved XUV emission and absorption spectroscopy. Spectra of the reemitted radiation (the albedo) for different C-, O-, F-, or Cl-containing plastic materials are presented. Depending on the material, the typical total (frequency-integrated) reemission is in the range of ≈10% of the gold reemission. By measuring the absorption spectra it was possible to follow the burnthrough in carbon from the initial solid degenerate state up to a high ionization state with absorption lines due to hydrogen-like carbon corresponding to a temperature of about 100 eV. The propagation of the heat wave into the material also has been studied by observing the emission from boron tracer layers embedded at different depths in the plastic foil. The experimental observations are compared with MULTI simulations.

We considered an ignition strategy based on energy injection in the final stages of the target implosion, but well before stagnation. The injected energy is used to set on a high adiabat the small portion of the fuel destined to become the ignition spark. Most of the energy needed to form the spark is provided by the work of the imploding target on the spark fuel. This approach is first introduced by a simple analytical model and then illustrated by 2D numerical calculations, in which the ignition of imploding cylinders by heavy ions is simulated. Different implosion designs and burn modes are presented and discussed. When compared with the standard central self-generated spark, or the fast ignition approaches, the ignition by entropy injection is potentially promising of some distinct advantages.

A Q-switched ruby laser, focussed by means of both gas and glass lenses, was used to irradiate massive planar carbon targets. Two different laser configurations were used, giving differing spatial beam qualities. Faraday cups positioned at various angles about the target were used to monitor ion flow properties of the resulting laser-produced plasmas. These flow properties were used to compare the laser-plasma producing characteristics of the lenses.

Volume 23, Number 1, Pages 55–59, 2005

Below is the complete Reference citation for Neumayer et al. (2005).

Neumayer, P., Bock, R., Borneis, S., Brambrink, E., Brand, H., Caird, J., Campbell, E.M., Gaul, E., Goette, S., Haefner, C., Hahn, T., Heuck, H.M., Hoffmann, D.H.H., Javorkova, D., Kluge, H.-J., Kuehl, Th., Kunzer, S., Merz, T., Onkels, E., Perry, M.D., Reemts, D., Roth, M., Samek, S., Schaumann, G., Schrader, F., Seelig, W., Tauschwitz, A., Thiel, R., Ursescu, D., Wiewior, P., Wittrock, U. & Zielbauer, B. (2005). Status of PHELIX laser and first experiments. Laser Part. Beams23, 87–93.

Generation of large amplitude plasma waves using high-power lasers in either the wakefield or beat-wave scheme is considered. We show how the nonlinear behavior of the plasma wave may make it advantageous to split the total energy into more than one pulse in the wavefield scheme. When a beat wave is generated by a pulse of finite length, we show how the final wave amplitude may be enhanced if the frequency of one or both pulses is chirped in such a way that the wavelength of the beat increases from the front to the back of the pulse.

Electron plasma waves excited and/or modified by finite objects such as laser and charged particle pulses are investigated nonperturbatively using a simple model where the driver is unaffected by the interaction. It is shown that smooth as well as sharply peaked electron plasma wake waves of large amplitude can exist. In particular, two charged pulses moving in tandem can excite a highly localized electron plasma wave without producing the expected long wake wave, a configuration that should be particularly useful for efficient trapping and acceleration of electrons to high energies.

The hot spot heating process by an assumed deuteron beam is evaluated in order to estimate the contribution of the energy produced by the deuteron beam-target fusion to the heating process. The deuteron beam energy versus the number of deuterons is evaluated through the experimentally achieved proton beam energy distribution using the TRIDENT short pulse laser at the Los Alamos National Laboratory (LANL). The corresponding hot spot heating is then calculated using this assumed deuteron beam spectrum. The resulting first order heating dynamics is employed in the expanded “bonus” energy calculation, and a 12.73% extra energy from deuteron beam-target fusion was found with the assumed deuteron spectrum when ρrb = 4.5 g/cm2 is considered, where ρ is the fuel density, and rb is the ion beam focusing radius on the target. The results provide further insight into the contribution of the extra heat produced by deuteron beam-target fusion to the hot spot ignition process. A further analysis of how a converter foil using ultra-high-density cluster materials can help to achieve the yield requirements for ignition is presented.

The emissions to the atmosphere, by a heavy ion inertial fusion reactor in accidental and normal operations, are in form of tritium gas with two chemicals forms of tritium: HT and HTO. Emissions of 100% HT have been analyzed in this work, and their consequences in the dosimetry. The primary phase of the emission depends on the atmospheric conditions. As a consequence, the tritium is dispersed far from the source. The HT can be oxidized in the stratosphere or in the surface by microbiological action to convert it to HTO, and back to the air in a reemission process or penetrate into the subground. In the form of HT, the effective dose equivalent (EDE) is important in the case of intake (inhalation, skin absorption, or ingestion), because tritium is a beta emitter of low energy and the dose by external uptake is not considerable. Thus, the dose by ingestion contributes the most to the total dose in the case of HT rather than HTO. It constitutes 98% of the total EDE, in contrast with the contribution to the total dose by HTO, which is only 40%.

An atomic model to describe the density and temperature effects on inelastic electron-ion collisions in dense plasmas is presented. This model has been used for Na-like iron to compute the optically allowed and forbidden collision rates from the ground configuration 1s2 2s2 2p6 3s to the 1s2 2s2 2p6 41 excited levels with l = 0,1,2. The focus is on temperature and density ranges 100–300 eV and 1022–1024 cm-3.

The target chamber of an inertial confinement fusion (ICF) power plant or high-yield test facility must be designed to absorb the target produced Xrays and ions and survive the resulting effects. The target chamber conditions must be restored in fractions of a second for high repetition rate power applications. Computer modeling of these phenomena is essential because equivalent conditions cannot be produced in laboratory experiments prior to the first ignition of high-yield ICF targets. Choices of models are dictated by specific reactor design strategies. The two major strategies, gas protection and sacrificial first surfaces, are used as a guide to our discussion. Physical models for ion, electron, and X-ray deposition are discussed, along with physical and numerical modeling of the resulting phase changes intarget chamber structures. The hydrodynamics and radiative transfer in the target chamber vapors and plasmas are central topics.

A plasma production method using the irradiation of an array of small spots has been investigated from the point of view of soft X-ray laser generation in the recombining plasma scheme pumped by a pulse-train laser. The expansion geometry of highly ionized ions produced by the micro-dot array irradiation method has been measured and compared with that by a simple line irradiation. Spatial distribution of gain coefficients of the Li-like Al ion transition lines have also been measured for both irradiation methods. Highly ionized ions were observed to spread wider in the micro-dot array irradiation method. It is expected that rapid expansion and efficient cooling are achieved in plasmas produced by the micro-dot array irradiation method, which is consistent with the experimental results on the spatial structure of the X-ray laser gain region.

The present measurements of the components' surface resistance to laser-induced damage has been completed to facilitate development and construction of the “Luch” laser system, a four-channel Nd-phosphate glass laser with a full output energy of E = 14–16 kJ. The study describes a method that, with a series of experimental data obtained from a single sample, allows us not only to estimate the threshold fluences, but to take into account the statistical nature of the surface damage. In a number of experimental situations this method makes it possible to estimate damaging fluences even from the result of a single exposure of the studied surface. Estimated threshold fluences for various optical elements are presented: K8 glass, experimental phosphate laser glass KGSS-0180, high-reflecting and antireflecting thin-film coating of elements. The 1.054-μm radiation pulse with half-height duration of 4 ns and the irradiation spot of ∼4 mm in diameter were used in the experiment.

It is shown that beyond a virtual cathode the current of a magnetized steady-state thin annular electron beam in a drift tube may range from zero to the limiting current of the tube.

Effective suppression of transverse stimulated Raman scattering (TSRS) in a large-aperture potassium dihydrogen phosphate (KDP) crystal is an important scientific and technical problem in high-intensity laser research and applications. In this work, a method to suppress TSRS using pulse stacking is proposed. The method suppresses TSRS significantly, with greater numbers of subpulses producing more obvious suppression effects, and the threshold intensity growth rate of the 3ω laser in the KDP crystal reaches up to about 1.9 when the stacked pulse contains four subpulses. This suppression effect is attributed to the fact that the polarization directions of adjacent subpulses are perpendicular to each other. The method can be used to suppress other nonlinear effects, including transverse stimulated Brillouin scattering in large-aperture optical devices and stimulated rotational Raman scattering in long air paths.

A one-dimensional, time-dependent fluid code is presented that numerically solves the hydrodynamic equations together with the wave equation for a picosecond pulse laser heated plasma. The laser light absorption by classical inverse bremsstrahlung and the ponderomotive force are evaluated self-consistently from the computed electromagnetic field quantities. At oblique incidence of p-polarized 1·054 μm laser radiation the resonant electric field is saturated by plasma wave convection through the nonlinear density profile steepening prior to wave breaking.

The effect of surface finish on the evolution of ICF targets has been studied. As driver for the implosion has been used a temporally profiled thermal radiation pulse (25 ns in duration) as that expected for the case of a high-gain (cm sized) capsule enclosed in a cavity. 2-D numerical simulations have been performed on a planar analog to investigate the stability to perturbations having wavelengths in the interval 2.5–40 μm and initial amplitudes of 0.03 and 1 μm. The simulations show perturbation growing due to hydrodynamic instabilities. The distortion of the ablation front reaches such a level to strongly enhance the ablation rate because of the increase in the exposed area and in the power absorbed per unit area. Two different phenomena have been identified: one, preferentially occurring for small wavelengths, in which the motion behind the first shock wave becomes turbulent and the symmetry is lost; the other, appearing for long wavelengths, in which a thermal radiation wave penetrates into the fuel. This preheating phenomenon is related to the formation of holes in the thermal shield due to the enhanced ablation and to matter transverse piling up. All these effects may render useless the 1-D-based design of a high-gain capsule exposed to a given thermal bath. However, it has been also observed that, for the longer wavelength (40 μm) and a smaller initial perturbation amplitude (e.g. 0.01 μm), during the temperature pulse the preheating does not occur and most of the fuel can be accelerated as a whole to speeds of the order of 2 × 107 cm/s or greater without a substantial onset of transverse velocities, even in the presence of the ablator piling up.