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 possibility of an X-ray laser by irradiation of muon beams on a thin rod of deuterium-tritium mixture is discussed. The excited state of dtμ-mesomolecules (J, v) = (1, 0) can be induced to make radiative chain transitions with photon energy of 90 eV to the ground state (0, 0), evacuated by fusion.

In this article, the results of experimental and numerical studies of the behavior of perturbed interface between air and helium are presented. The interface is initially accelerated by the incident shock wave coming from air to helium and then decelerated by a series of reflected shock waves. Two types of initial interface perturbations like “saw” and “step” are considered.

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.

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.

The results of numerical simulation of the neutron generation process in the cone lead targets exposed to laser irradiation are presented. The experimental time dependence of the target shell is used as a boundary condition for the hydrodynamic equations. Deuterium compression is calculated on the assumption that some part of the shell that continues to move inward onto the conical target is decelerated by deuterium in the absence of the reactive force. The behavior of deuterium is described by the 2D equations of two temperature gas dynamics with the electron and ion contributions to the heat conduction taken into account. The behavior of lead is described by the 2D equations of gas dynamics closed by the real wide range equation of state (EOS). The neutron yield in the experiments under discussion is caused by short duration steep rises of the ion temperature generated by the collapse of the heading shock wave and the first reflected one. The stage of adiabatic compression of the high-temperature plasma was lacking in the experiment due to the small mass of the shell.

Laser-induced damage threshold (LIDT) is an important parameter used to describe the resistance of optical thin films to laser damage. The service life and cost of optical systems depend on the LIDT of the film. Thus, the precision with which the film's LIDT can be measured impacts how well the service life and cost of the system can be predicted. Therefore, it is important to find a precise approach to diagnose a film's laser-induced damage. In this paper, characteristics of the peak sound pressure of laser-induced plasma shock waves from thin films have been systematically investigated experimentally. We found that the peak sound pressure decays rapidly with propagation distance during air transmission. Based on a theoretical analysis of the relationship between the peak sound pressure and the laser damage to a film, we propose a method for diagnosing laser damage using the peak sound pressure of a thin film's shock wave. Our results show that this method can simplify implementation, which will provide a new method with which to diagnose laser damage to thin films.

This paper presents the results of theoretical and experimental studies on high-pressure He-Cd and He-Zn lasers. It is shown that using the hard ionizer approximation makes it possible to readily and efficiently simulate the plasma chemical processes that occur in the active media of high-pressure lasers pumped by electron and ion beams as well as by nuclear reaction products in electron-beam experiments. Laser oscillation was achieved at λ = 325, 441.6, 533.7, and 537.8 nm for the cadmium ion and at λ = 610.3 nm for the zinc ion.

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.

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.

We have performed a kinetic study of the electron dynamic relaxation inside a Au film subjected to a subpicosecond laser pulse. For this purpose, we have developed a time-dependent numerical solution of the Boltzmann equation for the electrons inside the film considering the collision integrals due to electron–electron and electron–phonon collisions and a perturbation term due to the laser pulse. Our results show that, after the pulse excitation, electron distributions are very far from equilibrium. Therefore it is not possible, especially in the first part of the temporal evolution, to describe the relaxation of the electron distribution through a two-temperature model.

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.

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.

Experimental investigations of laser-produced plasma expansion in a strong (−20 T) magnetic field have been carried out. The image and spectra of the plasma flame in the soft X-ray spectral region have been obtained. It has been shown that the strong magnetic field limits the transverse plasma expansion and strongly effects the ion-level populations.

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.

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.

The recombination X-ray laser scheme is considered in the case of recombining plasmas produced by laser pulses which are short to such a degree that the condition for inversion in X-ray transitions of the ions is essentially time-dependent. Using an analytic four-level model, applicable for H-like and Li-like ions, we calculate the inversion conditions for the 4→3, 3→2, and 2→l transitions in H-like ions as functions of time. As we have already shown, a drastic change occurs, especially for the 3→2 transition. To achieve inversion, for short times the free-electron density as a function of the temperature Te, Neinv(Te), must be greater than a critical density Nesh (Te), Neinv(Te) > Nesh(Te), whereas for longer times in the quasi-steady state, Neinv(Te) must be smaller than a critical density Neqv(Te), Neinv(Te) < Nequ(Te). We also consider the evolution of the inversion condition in the intermediate time domain. The time duration of the existence of the short-time 3→2 inversion condition–in the time interval from the initial state with unoccupied lower levels to the quasi-steady state—is in the main determined by t α 1/A21; for example, one has t ≈ 730 fs for Na.

In a plasma produced in particular by optical-field ionization, during the initial cascade populating the excited levels, an inversion may be possible in the 2→1 resonance line transition in the transient regime. The inversion in this transition is of interest especially because of the arising possibility to achieve X-ray gain at shorter wavelengths. In the transient case, an inversion occurs for a small time depending on the temperature Te and the density N.

In addition, we discuss generally the time behavior of the population densities (especially of N3) and show that an optimal population density occurs, on the one hand, for very short times (fs region, depending on Z). On the other hand, however, the optimal (ion-)density-temperature relation is determined via a time of the optimal population density required with regard to the experimental conditions.

This paper considers various channels of electron–positron pair, neutron, and γ-quantum generation via the ultrashort high-power laser pulse interaction with targets made from different materials. The positron yields in materials with different Z are estimated for the positron production by high-speed electrons and γ-photons. It is shown that a picosecond 100-TW laser pulse gives rise to formation of about 1010 positrons, possible channels of the neutron production in light- and heavy-atom materials being studied as well. It is ascertained that the formation of up to 107 laser neutrons per shot is possible when the laser intensity is ∼1021 W/cm2 on a heavy-atom target.

This paper presents an analysis of relativistic self-focusing of a Gaussian laser beam incident normally on a plane interface of a linear medium and a nonlinear, nonabsorbing plasma with an intensity dependent dielectric constant. Considering the nonlinearity to arise from the relativistic variation of mass and the Lorentz force on electrons. Following Wentzel–Kramers–Brillouin (WKB) and paraxial ray approximation the phenomenon of relativistic self-focusing of the transmitted laser radiation has been analyzed for the arbitrary magnitude of nonlinearity. Change in the intensity distribution along the wavefront of the Gaussian beam, due to refraction at the interface has also been taken into account. The variation of beamwidth parameter with distance of propagation, self trapping condition and critical power has been evaluated. Numerical estimates for typical parameters of laser plasma interaction process indicate the refraction at the interface to have a significant effect on self-focusing.