This work presents an investigation of the self-focusing of a high-power laser beam having cosh Gaussian intensity profile in a collissionless plasma under weak relativistic-ponderomotove (RP) and only relativistic regimes and its effect on the excitation of electron plasma wave (EPW), and particle acceleration process. Nonlinear differential equations have been set up for the beam width and intensity of cosh Gaussian laser beam (CGLB) and EPW using the Wentzel-Kramers-Brillouin and paraxial-ray approximations as well as fluid equations. The numerical results are presented for different values of decentered parameter ‘b’ and intensity parameter ‘a’ of CGLB. Strong self-focusing is observed in RP regime as compared with only relativistic nonlinearity. Numerical analysis shows that these parameters play crucial role on the self-focusing of the CGLB and the excitation of EPW. It is also found that the intensity/amplitude of EPW increases with b and a. Further, nonlinear coupling between the CGLB and EPW leads to the acceleration of electrons. The intensity of EPW and energy gain by electrons is significantly affected by including the ponderomotive nonlinearity. The energy of the accelerated electrons is increased by increasing the value of ‘b’. The results are presented for typical laser and plasma parameters.

We use an Eulerian Vlasov code to study the efficient ion acceleration in dense targets by the ponderomotive force of a high-intensity circularly polarized laser beam, normally incident on a dense plasma. The code solves the one-dimensional relativistic Vlasov–Maxwell equations for both electrons and ions. We follow in details the mechanism of formation and evolution of a double-layer structure, where electrons are pushed steadily in the forward direction by the ponderomotive force of the laser beam, trapping an ion population, while an induced space charge electric field pulls ions behind them, forming a double-layer structure supported by the strong ponderomotive pressure of the intense laser beam. We consider the case of a high-density deuterium plasma with n/ncr = 100, where ncr is the critical density. Three cases are studied, by varying the width of the dense target and the intensity of the laser beam (with the normalized vector potential or quiver momentum a0 = 50 and a0 = 100), to follow the physical processes involved in the ion acceleration and the final formation of a neutral plasma jet ejected from the back of the target. We follow the transition from a situation where the laser pulse radiation pressure is acting on the double layer in the target, to a situation where below a given thickness a fraction of the laser energy is transmitted through the target. The absence of noise in the Eulerian Vlasov code allows us to follow accurately the evolution of the phase-space structures of the distribution functions.

A self-guided Gaussian laser pulse propagating in a non-uniform plasma channel is unstable to a plasma wave perturbation co-moving with the laser with its group velocity. The plasma wave amplitude has a maximum radial profile along the laser propagation axis. As the plasma wave propagates through a non-uniform plasma channel, the plasma wave perturbation causes focusing in the part of the laser that propagates with the electron density trough and defocusing in the part moving with the crest. This yields an axial gradient in the intensity of the laser and produces a ponderomotive force on the electrons. The ponderomotive force drives the plasma wave, which in turn makes the modulational instability grow. The growth rate of the modulational instability becomes larger with the increase in non-uniformity of a shallow plasma channel. In a deep cavitated plasma channel the growth rate of the modulational instability increases with the laser pulse amplitude.

Laser-driven relativistic electrons can be focused onto a high-Z convertor for generating high-brightness γ-rays, which in turn can be used to induce photonuclear reactions. In this work, photo-transmutation of long-lived radionuclide 135Cs induced by laser–plasma–interaction-driven electron source is demonstrated using Geant4 simulation (Agostinelli et al., 2003 Nucl. Instrum. Meth. A506, 250). High-energy electron generation, bremsstrahlung, as well as photonuclear reaction are observed at four different laser intensities: 1020, 5 × 1020, 1021, and 5 × 1021 W/cm2. The transmutation efficiency depends on the laser intensity and target size. An optimum laser intensity, namely 1021 W/cm2, was found, with the corresponding photonuclear reaction yield reaching 108 J−1 of the laser energy. Laser-generated electrons can therefore be a promising tool for transmutation reactions. Potential application in nuclear waste management is suggested.

The paper presents a cylindrical diode with a rod anode for repetitive pulsed intense X-ray sources. The diode uses a massive anode of diameter 1 cm, thus increasing the lifetime of the energy converter. The diode gap is preliminary filled with ions produced by cathode flare in a vacuum discharge, allowing electron beam pinching at a voltage of <200 kV. In the mode of pinching, the diode is an efficient source of high-power X rays. At a distance of 20 cm from the X-ray source, the radiation dose per pulse is 0.4 R at a peak power of 7 × 106 R/s. The full-width at half-maximum of the radiation pulse is 40 ns. The power in the diode is 1.8 GW at a beam current of 10 kA and exceeds the maximum power of the generator operating onto a matched load with constant resistance.

In the interaction of ultra-short and ultra-intense high contrast laser pulse with a dense foil, accelerating electron sheath is formed. The dynamic of this sheath is obtained according to the ponderomotive force of the laser pulse and restoring electrostatic force of the stationary heavy ions. In the transient dynamics, maximum electron sheath displacement is obtained for different interaction parameters. This maximum displacement has an important effect in the explanation of the electron blow out condition. It is shown numerically that the electron sheath maximum displacement increases with increasing laser pulse amplitude or decreasing its rise time, or by decreasing plasma electron density. Recently, backward MeV acceleration of electrons in the interaction of intense laser pulse with solid targets was observed. The ponderomotive force of the compressed reflected laser pulse includes in our formalism and is used for explanation of the electron's backward acceleration. The threshold values of the interaction parameters for the occurrence of this phenomenon are considered. The electron blow out condition and backward acceleration are accompanied with numerical modeling and 1D3V, particle-in-cell simulation code.

An exploding wire system has been experimentally studied by the observation of its plasma dynamics and the electrical energy delivered by the supporting circuit to the metallic wire. Plasma radial expansion has been obtained from visible light streak images, meanwhile electrical energy transfer dynamics was derived from the analysis of voltage and current traces of the exploding wire circuit. In these measurements, a significant portion of the electrical energy has been transferred to the exploding wire circuit during the plasma expansion, and lower limits for the resistivity during the plasma expansion confirm the existence of a central liquid or solid metallic core in addition to the expanding plasma.

We survey the present status and potentialities of diagnostics for arbitrary magnetized plasmas of inertial confinement fusion concern. These diagnostics include: Faraday rotation, inverse Faraday effect, Thomson scattering, Stark–Zeeman line broadening as well as proton stopping for any ratio, of the particles plasma frequency to cyclotron frequency. This presentation is timely motivated by recent experiments highlighting laser-produced kilo Teslas and nearly steady magnetic fields in inertial fusion plasmas. Positive synergies due to diagnostics combinations are also addressed.

Most of the high-energy laser systems deliver temporally super-Gaussian-shaped laser pulses. The propagation properties of this kind of pulses in a nonlinear medium are studied in this paper. There is Stokes component in the sideband spectrum of super-Gaussian-shaped pulses, and the frequency difference between the Stokes component and the center frequency is equals to the Brillouin frequency of the nonlinear medium. When the laser is reflected by optical elements in the light path, Stokes component in the reflected light can be amplified by the subsequent part of the laser pulse and excite stimulated Brillouin scattering (self-pumped SBS). The self-pumped SBS is studied theoretically and experimentally, and the experimental results agreed well with the calculated results. The simulation results show that lower-order super-Gaussian-shaped pulses are more suitable for suppressing the self-pumped SBS and of great benefit to the energy delivering of the high-power laser pulses. To the best of our knowledge, this is the first time to experimentally demonstrate the self-pumped SBS of high-power super-Gaussian-shaped laser pulses.

In this paper, a three-dimensional (3D) model as a new module of LAP3D code is presented to study the crossed-beam energy transfer (CBET) process. This model is not limited by the paraxial approximation and can be used to deal with a large crossing angle case. Besides, this model is also appropriate for the multi-ion species conditions and even multi-beams problems, which will be very helpful in relevant experiment analysis and the target design. In our 3D simulations, we take the overlapped beams with a 60° crossing angle as an example, and observe obvious energy transfer process, which indicates CBET process might occur between the incident laser beams with a large crossing angle when the matching condition is satisfied. This large crossing angle CBET process also can change the spatial shape of the beam spot, and may have some potential important influence on other laser–plasma interaction instabilities and the energy symmetry in hohlraum.

We analyze the undulator radiation from planar bi-harmonic undulators with account for all principle losses in real devices. The exact analytical expressions for the UR spectrum, intensity, and the line shape are obtained in terms of special functions. The interplay of various broadening contribution is elucidated and their role is explored. Suspension and boost of certain harmonics by fine tuning the undulator parameters is demonstrated. The constant non-periodic magnetic constituents are studied to compensate the divergency of the electronic beam. The examples of harmonic generation in various undulator schemes with single and double period magnetic field are explored. Influence of inhomogeneous and homogeneous broadening on these harmonics is demonstrated. The analysis is applied to evaluate the harmonics in self-amplified spontaneous emission free electron laser.

The paper presents a general theoretical framework and related Monte Carlo simulation of novel type of the X-ray sources based on relativistic Thomson scattering of powerful laser radiation. Special attention is paid to the linac X-ray generators by way of two examples: conceptual design for production of 12.4 keV photons and presently operating X-ray source of 29.4 keV photons. Our analysis shows that state-of-the-art laser and accelerator technologies enable to build up a compact linac-based Thomson source for the same X-ray imaging and diffraction experiments as in using of a large-scale X-ray radiation facility like a synchrotron or Thomson generator based on electron storage ring.

Second-harmonic generation by an obliquely incident s-polarized laser from an underdense plasma in the presence of a magnetic field has been investigated analytically. An expression for the relativistic factor γ has been obtained in the presence of magnetic field. The efficiency of second-harmonic radiation η has been obtained as a function of angle of incidence θ, normalized electric field amplitude of laser beam a0, normalized electron density ${\rm \omega} _{\rm p}^2 /{{\rm \omega} ^2}$, and magnetic field b. It is observed that γ increases with b. In turn, the conversion efficiency decreases with an increase in b. It is seen that the conversion efficiency is affected by the magnetic field due to the modified relativistic factor. In the absence of magnetic field, η increases with a0 and θ. However, in the presence of magnetic field, the conversion efficiency starts decreasing as the magnetic field is increased.

In the present work, classical electron–ion scattering, Coulomb logarithm, and stopping power are studied taking into account the quantum mechanical diffraction effect and the dynamic screening effect separately and together. The inclusion of the quantum diffraction effect is realized at the same level as the well-known first-order gradient correction in the extended Thomas–Fermi theory. In order to take the effect of dynamic screening into account, the model suggested by Grabowski et al. in 2013 is used. Scattering as well as stopping power of the external electron (ion) beam by plasma ions (electrons) and scattering of the plasma's own electrons (ions) by plasma ions (electrons) are considered differently. In the first case, it is found that in the limit of the non-ideal plasma with a plasma parameter Γ → 1, the effects of quantum diffraction and dynamic screening partially compensate each other. In the second case, the dynamic screening enlarges scattering cross-section, Coulomb logarithm, and stopping power, whereas the quantum diffraction reduces their values. Comparisons with the results of other theoretical methods and computer simulations indicate that the model used in this work gives a good description of the stopping power for projectile velocities $v\,{\rm \lesssim}\, 1.5 v_{{\rm th}}$, where vth is the thermal velocity of the plasma electrons.

A new approach is proposed to analyze Bremsstrahlung X-rays that are emitted from laser-produced plasmas (LPP) and are measured by a stack type spectrometer. This new method is based on a spectral tomographic reconstruction concept with the variational principle for optimization, without referring to the electron energy distribution of a plasma. This approach is applied to the analysis of some experimental data obtained at a few major laser facilities to demonstrate the applicability of the method. Slope temperatures of X-rays from LPP are determined with a two-temperature model, showing different spectral characteristics of X-rays depending on laser properties used in the experiments.

Stimulated Raman backward scattering of an X-mode laser beam propagating in a homogenous plasma is studied in the presence of a transverse magnetic field. As the laser propagates in its X-mode in plasma, it decays into an upper hybrid wave and a down-shifted sideband wave. Beating the incident laser with the sideband exerts a nonlinear ponderomotive force acting on plasma electrons driving the excited upper hybrid wave. The incident wave then parametrically couples with the upper hybrid wave to drive the sideband. Using the fluid model and nonlinear current density, the nonlinear ponderomotive force is obtained to find the dispersion relation of the scattered sideband wave and the growth rate of the instability in the weakly relativistic regime. It is shown that the growth rate decreases and the cut-off points in the normalized wave number of the upper-hybrid wave become smaller by increasing the static magnetic field.

In this paper, a heuristic algorithm based on particle-in-cell (PIC) simulation is introduced to investigate the harmonic generation during the ionization and formation of plasma by a non-relativistic laser field when it propagates through hydrogen atoms. The harmonic generation is considered for the radiative recombination of an ionized electron with its nearest ion. The ionization algorithm is improved by considering the Stark effect and nonzero velocity for ionized electrons. Energy conservation is evaluated during the recombination process. In our code, for the first time, Maxwell's equations are integrated for harmonic fields in a separate mesh using the artificial recombination current as a source term. The simulation results are then used to illustrate the intensity spectrum of generated fields. It is shown that the initial momentum of ionized electrons affects the harmonic spectrum because the energy of radiated photons varies with the electron energy.

The luminescence spectra of noble gases and their binary mixtures were measured using heavy ion beam excitation from a DC-60 accelerator. Spectra were measured in the range of 200–975 nm; the gas spectra were dominated by lines of p–s and d–p atomic transitions; in neon and argon, lines from atomic oxygen, N2, N2 +, and OH radical bands were also observed. The ultraviolet region of the spectra was represented by a “third continuum” of noble gases. In krypton, the band of the KrO excimer molecule with a maximum at 557 nm was also observed. The maxima of the heteronuclear ionic molecules bands were located at wavelengths of 329 and 506 nm (Ar–Xe), 491 nm (Kr–Xe), and 642 nm (Ar–Kr). The relative intensities of the 2p–1s transitions of the noble gases atoms were measured and are discussed.

An obliquely incident high-power laser (ω0, k0z) on the metallic surface can resonantly excite a surface plasma wave (SPW) (ω1, k1z) and a quasi-electrostatic plasma wave (ω, kz) inside the skin layer at the phase-matching conditions of frequency ω1 = ω − ω0 and wave number k1z = kz − k0z. The oscillating electrons in the skin layer couples with the seed SPW and exert non-linear ponderomotive force on electrons at the frequency of quasi-static mode. Density perturbations due to quasi-static mode and ponderomotive force associate with the motion of electrons (due to incident laser) and give rise to a non-linear current by feedback mechanism. At ω/kz ~ vF (where vF is the Fermi velocity of metal) this non-linear current is responsible for the growth of SPW. The maximum growth of the present process (≅1.5 × 1012 s−1) is achieved at incident angle θ = 42° for laser frequency ω0 = 2 × 1015 rad/s. Growth of SPW enhances from 1.62 × 1011 to ≅1.5 × 1012 s−1 as the magnetic field changes from 12 to 24 MG. The excited SPW can be utilized for surface heating and diagnostics purpose.

The present paper proposes a model for the generation of Terahertz (THz) radiation by self-focused hollow Gaussian beam (HGB) in collisionless magnetized rippled density plasma. At high intensities, the change in the electron mass occurs due to relativistic effect, introducing a nonlinearity in the plasma leading to the self-focusing of the HGB. The nonlinear interaction of this highly intense self-focused HGB with the electron plasma wave in the rippled density plasma, satisfying proper phase matching conditions, results in the resonant excitation of THz radiations at the beat frequency. We have studied the dependence of generated THz radiations on the order of the HGB as well as on the static background magnetic field. The results show that the intensity of the generated radiations is highly sensitive to both of these parameters. For the current scheme the power of the generated THz waves comes out to be of the order of Gigawatts.