The energy of protons accelerated by ultra-intense lasers in the target normal sheath acceleration (TNSA) mechanism can be greatly enhanced by the laser parameter optimization. We propose to investigate the optimization of laser parameters for proton acceleration using double laser pulses in TNSA mechanism. The sheath field generation at the rear side of the target is significantly affected by the introduction of second laser pulse in TNSA mechanism, and consequently, the energy of the accelerated protons is also modified. The second laser pulse was introduced with different delays to study its impact on proton acceleration. Our study shows that the interplay of laser intensity and pulse duration of both laser pulses affects the proton acceleration. It was found that the proton maximum energy is the function of both laser intensity and pulse duration. A number of simulations have been performed to obtain maximum proton energy data under different combinations of laser intensity and pulse duration for the two laser pulses. The simulation results account for the underline physics for the proton bunch energy and the sheath field as a function of pulse intensity and pulse delay.

Particle-in-Cell (PIC) simulation is an interpolation-based method on the Newton–Maxwell (N–M) system. Its well-known drawback is its shape/interpolation functions often causing the violation of continuity equations (CEs) at mesh nodes and that of Maxwell equations (MEs) at particles' positions. Whether this drawback can be overcome by choosing/solving suitable shape/interpolation functions is of fundamental importance for the PIC simulation. Until now, these shape/interpolation functions are usually subjectively chosen and, hence, always invoke the drawback. Here, we first investigate whether these shape/interpolation functions can be self-consistently solved by considering under what condition the CEs and the MEs can be satisfied anywhere. Strict mathematical analysis reveals that strict self-consistent shape/interpolation functions are unavailable. Only few approximately self-consistent shape/interpolation functions are luckily found by some authors. This fact drives us to present another universal interpolation-free strict method on the N–M system.

A one-dimensional steady-state model for stimulated Raman backscatter (SRS) and stimulated Brillouin backscatter (SBS) processes in laser-irradiated plasmas is presented. Based on a novel “predictor-corrector” method, the model is capable to deal with broadband scattered light and inhomogeneous plasmas, exhibiting robustness and high efficiency. Influences of the electron density and temperature on the linear gains of both SRS and SBS are investigated, which indicates that the SRS gain is more sensitive to the electron density and temperature than that of the SBS. For the low-density case, the SBS dominates the scattering process, while the SRS exhibits much higher reflectivity in the high-density case. The nonlinear saturation mechanisms and competition between SRS and SBS are included in our model by a phenomenological method. The typical anti-correlation between SRS and SBS versus electron density is reproduced in the model. Calculations of the reflectivities are qualitatively in agreement with the typical results of experiments and simulations.

In this paper, we report on the acceleration of protons and oxygen ions from tens of micrometer large water droplets by a high-intensity laser in the range of 1020 W/cm2. Proton energies of up to 6 MeV were obtained from a hybrid acceleration regime between classical Coulomb explosion and shocks. Besides the known thermal energy spectrum, a collective acceleration of oxygen ions of different charge states is observed. 3D PIC simulations and analytical models are employed to support the experiential findings and reveal the potential for further applications and studies.

We investigate the Weibel instability (WI) in a dusty plasma which is driven to oscillation by the addition of dust grains in the plasma. Our analysis predicts the existence of three modes in a dusty plasma. There is a high-frequency electromagnetic mode, whose frequency increases with an increase in the relative number density of dust grains and which approaches instability due to the presence of dust grains. The second mode is a damping mode which exists due to dust charge fluctuations in plasma. The third mode is the oscillating WI mode. The dispersion relation and the growth rate of various modes in the dusty plasma are derived using the first-order perturbation theory. The effect of dust grain parameters on frequency and growth rate is also studied and reported.

Electron dynamics in an axially localized large amplitude electron Bernstein mode in a magnetic mirror is studied. The mode is localized due to plasma density and magnetic field profiles and could be driven by an electron cyclotron wave, launched from outside, via linear mode conversion. Energetic electrons of finite gyro-radius resonantly interact with the mode and gain primarily transverse energy favoring stronger mirror confinement. At Bernstein wave normalized amplitude of A00 = 0.01 and for other normalized parameters Zn0 = 40, k⊥c/ω = 10, ${L}^{\prime}_m = 215$, ωc0/ω = 0.9, ψn0 = 3π/2, the electrons can gain energy in the hundreds of keV range.

We study the influence of finite-emittance electron bunches in the bubble regime of laser-driven wakefield acceleration onto the microscopic structure of the bunch itself. Using resilient backpropagation (Rprop) to find the equilibrium structure, we observe that for realistic and already observed emittances the previously found crystalline structures remain intact and are only widened marginally. Higher emittances lead to larger electron displacements within the crystal and finally its breaking.

In this paper, we have investigated the relativistic electron acceleration by plasma wave in an axially magnetized plasma by considering the self-magnetic field effects. We show that the optimum value of an external axial magnetic field could increase the electron energy gain more than 40% than that obtained in the absence of the magnetic field. Moreover, results demonstrate that the self-magnetic field produced by the electric current of the energetic electrons plays a significant role in the plasma wakefield acceleration of electron. In this regard, it will be shown that taking into account the self-magnetic field can increase the electron energy gain up to 36% for the case with self-magnetic field amplitude Ωs = 0.3 and even up to higher energies for the systems containing stronger self-magnetic field. The effects of plasma wave amplitude and phase, the ion channel field magnitude, and the electron initial kinetic energy on the acceleration of relativistic electron have also been investigated. A scaling law for the optimization of the electron energy is eventually proposed.

In this study, an atmospheric pressure dielectric barrier discharge-based argon plasma jet has been modeled using COMSOL Multiphysics, which is based on the finite element method. The fluid dynamics and plasma modules of COMSOL Multiphysics code have been used for the modeling of the plasma jet. The plasma parameters, such as electron density, electron temperature, and electrical potential, have been examined by varying the electrical parameters, that is, supply voltage and supply frequency for both cases of static and with the flow of argon gas. The argon gas flow rate was fixed at 1 l/min. Ring electrode arrangement is subjected to a range of supply frequencies (10–25 kHz) and supply voltages (3.5–6 kV). The experimental results of the ring electrode configuration have been compared with the simulation analysis results. These results help in establishing an optimized operating range of the dielectric barrier discharge-based cold plasma jet in the glow discharge regime without arcing phenomenon. For the applied voltage and supply frequency parameters examined in this work, the discharge was found to be consistently homogeneous and displayed the characteristics of atmospheric pressure glow discharge.

The nonlinear evolution of electron Weibel instability in a symmetric, counterstream, unmagnetized electron–positron e−/e+ plasmas is studied by a 2D particle-in-cell (PIC) method. The magnetic field is produced and amplified by the Weibel instability, which extracts energy from the plasma anisotropy. A weakly relativistic drift velocity of 0.5c is considered for two counterstreaming e−/e+ plasma flows. Simulations show that in a homogeneous e−/e+ plasma distribution, the magnetic field amplifies exponentially in the linear regime and rapidly decays after saturation. However, in the case of inhomogeneous e−/e+ plasma distribution, the magnetic field re-amplifies at post-saturation. We also find that the amount of magnetic field amplification at post-saturation depends on the strength of the density inhomogeneity of the upstream plasma distribution. The temperature calculation shows that the finite thermal anisotropy exists in the case of an inhomogeneous plasma distribution which leads to the second-stage magnetic field amplification after the first saturation. Such density inhomogeneities are present in a variety of astrophysical sources: for example, in supernova remnants and gamma-ray bursts. Therefore, the present analysis is very useful in understanding these astrophysical sources, where anisotropic density fluctuations are very common in the downstream region of the relativistic shocks and the widely distributed magnetic field.

In this manuscript, the time-resolved laser-induced breakdown spectroscopy (LIBS) on tungsten target in air and the coexistence of LTE among atoms and ions as well as the fulfillment of optically thin plasma condition are reported. The laser-induced plasma (LIP) of tungsten is generated by focusing the second harmonic of a Q-switched Nd:YAG laser of pulse width ~7 ns and repetition rate of 1 Hz on the tungsten target. The temporal evolution of LIP of tungsten is recorded at four different incident laser fluences of 60, 120, 180, and 270 J/cm2. The several atomic and singly ionized lines of tungsten are identified in LIP. For the estimation of plasma temperature via the Boltzmann plot, the transitions at 430.7, 449.4, 468.0, 484.3, 505.3, and 524.2 nm of Atomic transition of tungsten (WI) and that of the ionic transitions, First Ionic transition of Tungsten (WII) at 251.0, 272.9, and 357.2 nm are selected. The electron density is estimated using the Stark-broadened profile of WI line at 430.2 nm. The McWhirter criteria for the local thermodynamic equilibrium (LTE) condition is verified in present experimental conditions as well as the relaxation time and diffusion length are estimated to take into account the transient and inhomogeneous nature of the plasma. The optically thin plasma condition is studied by assessing the experimental intensity ratio of atomic lines and compared with that of the theoretical intensity ratio (branching ratio). The signal to noise ratio (SNR) is also obtained as a function of time with respect to laser pulse and incident laser fluence. All these observations indicate that the spectra should be recorded within the temporal window of 1–3.5 µs with respect to laser pulse where the plasma can be treated as optically thin as well as under LTE simultaneously along with the large SNR.

The plasma parameters of laser-ablated Zirconium (Zr) using a Langmuir probe technique have been investigated by employing a Q-switched Nd:YAG laser (532 nm, 6 ns) at various irradiances ranging from 8.6 to 15.5 GW/cm2. All the measurements have been performed under an ultra-high vacuum condition while keeping the probe at a fixed distance of 4 mm from the target. By varying the biasing voltages from 1 to 75 V, the corresponding values of electric currents are measured by the probe on the oscilloscope. Laser-induced Zr plasma parameters such as electron temperature, electron number density, plasma potential, Debye length, and thermal velocity have been evaluated from I–V characteristic curves of Langmuir probe data. It is found that both the electron temperature and thermal velocity of Zr plasma reveal an increasing trend from 18 to 41 eV and 2.8 × 108 to 4.3 × 108 cm/s, respectively, with increasing laser irradiance which is attributed to more energy deposition and enhanced ablation rate. However, the electron number density of Zr plasma exhibits a non-significant increase from 6.5 × 1014 to 6.7 × 1014 cm−3 with increasing irradiance from 8.6 to 10.9 GW/cm2. A further increase in irradiance from 12 to 15.5 GW/cm2 causes a reduction in the number density of Zr plasma from 6.1 × 1014 to 5.6 × 1014 cm−3 which is attributed to the formation of thick sheath, ambipolar electric field, and laser-supported detonation waves (Shock front). Scanning electron microscope analysis has been performed to reveal the surface morphology of irradiated Zr. It reveals the formation of cracks, ridges, cones, and grains. It was observed at high irradiances the ridges are vanished, whereas cones and cracks are dominant features. By controlling plasma parameters, surface structuring of materials can be controlled, which has a vast range of applications in the industry and medicine.

The ablation and acceleration of diamond-like high-density carbon foils irradiated by thermal X-ray radiations are investigated with radiation hydrodynamics simulations. The time-dependent front of the ablation wave is given numerically for radiation temperatures in the range of 100–300 eV. The mass ablation rates and ablation pressures can be derived or implied from the coordinates of ablation fronts, which agree well with reported experiment results of high-density carbon with radiation temperatures Trad in the range of 160–260 eV. It is also found that the $T_{{\rm rad}}^3$ scaling law for ablation rates does not apply to Trad above 260 eV. The trajectories of targets and hydrodynamic efficiencies for different target thicknesses can be derived from the coordinates of ablation fronts using a rocket model and the results agree well with simulations. The peak hydrodynamic efficiencies of the acceleration process are investigated for different foil thicknesses and radiation temperatures. Higher radiation temperatures and target thicknesses result in higher hydrodynamic efficiencies. The simulation results are useful for the design of fusion capsules.

We present the experimental optimization of electrons in the several hundred keV energy range originated from laser-irradiated wire targets. Accelerated by a femtosecond laser pulse, an electron pulse emitted from the wire target was collimated immediately along the wire to a filter unit for the manipulation of energy and spatial distributions. It is shown in simulation that with a pair of magnets as the filter unit, the optimized electrons could serve as a compact and tunable electron source. The proposed system was demonstrated in a proof-of-principle experiment where we attained 1 fC bunch charge with transverse coherence length approaching 1 nm based on a 0.2 TW laser platform. This indicates the scheme as a promising candidate for single-shot electron diffraction.

The theoretical investigation of shocks and solitary structures in a dense quantum plasma containing electrons at finite temperature, nondegenerate cold electrons, and stationary ions has been carried out. A linear dispersion relation is derived for the corresponding electron acoustic waves. The solitary structures of small nonlinearity have been studied by using the standard reductive perturbation method. We have considered collisions to be absent, and the shocks arise out of viscous force. Furthermore, with the help of a standard reductive perturbation technique, a KdV–Burger equation has been derived and analyzed numerically. Under limiting cases, we have also obtained the KdV solitary profiles and studied the parametric dependence. The results are important in explaining the many phenomena of the laser–plasma interaction of dense plasma showing quantum effects.

This article presents a preliminary study of the longitudinal self-compression of ultra-intense Gaussian laser pulse in a magnetized plasma, when relativistic nonlinearity is active. This study has been carried out in 1D geometry under a nonlinear Schrodinger equation and higher-order paraxial (nonparaxial) approximation. The nonlinear differential equations for self-compression and self-focusing have been derived and solved by the analytical and numerical methods. The dielectric function and the eikonal have been expanded up to the fourth power of r (radial distance). The effect of initial parameters, namely incident laser intensity, magnetic field, and initial pulse duration on the compression of a relativistic Gaussian laser pulse have been explored. The results are compared with paraxial-ray approximation. It is found that the compression of pulse and pulse intensity of the compressed pulse is significantly enhanced in the nonparaxial region. It is observed that the compression of the high-intensity laser pulse depends on the intensity of laser beam (a0), magnetic field (ωc), and initial pulse width (τ0). The preliminary results show that the pulse is more compressed by increasing the values of a0, ωc, and τ0.

This paper presents the results of comprehensive studies of the efficiency of a pulsed electron beam transmission through a mixture of gases: nitrogen (83%), carbon dioxide (14%), and oxygen (2.6%) in the presence of ash and water vapor. The studied concentrations correspond to the concentrations of nitrogen, oxygen, and carbon dioxide in flue gas. The pressure and concentration of water vapor and ash in the drift chamber varied (375, 560, and 750 Torr; humidity 15 ± 5% and 50 ± 15%). The charge dissipation of a pulsed electron beam in the gas mixture in the presence of ash and water vapor was investigated, as well as the effect of the concentration of water vapor and ash on the geometric profile of the pulsed electron beam.

We study dynamics, structure and organization of the new paradigm of wavewrinkle structures associated with multipulse laser-induced RayleighTaylor (RT) instability in the plane of a target surface in the circumferential zone (C-zone) of the spot. Irregular target surface, variation of the fluid layer thickness and of the fluid velocity affect the nonlinearity and dispersion. The fluid layer inhomogeneity establishes local domains arranged (organized) in the «domain network». The traveling wavewrinkles become solitary waves and latter on become transformed into stationary soliton wavewrinkle patterns. Their morphology varies in the radial direction ofaussian-like spot ranging from the compacton-like solitons to the aperiodic rectangular waves (with rounded top surface) and to the periodic ones. These wavewrinkles may be successfully juxtapositioned with the exact solution of the nonlinear differential equations formulated in the KadomtsevPetviashvili sense taking into account the fluid conditions in particular domain. The cooling wave that starts at the periphery by the end of the pulse causes sudden increase of density and surface tension: the wavewrinkle structures become unstable what causes their break-up. The onset of solidification causes formation of an elastic sheet which starts to shrink generating lateral tension on the wavewrinkles. The focusing of energy at the constrained boundary causes the formation of wrinklons as the new elementary excitation of the elastic sheets.

Using a combination of laser–plasma interactions and magnetic confinement configurations, a conceptual fusion reactor is proposed in this paper. Our reactor consists of the following: (1) A background plasma of boron11 and hydrogen ions, plus electrons, is generated and kept for a certain time, with densities of the order of a mg/cm3 and temperatures of tens of eV. Both the radiation level and the plasma thermal pressure are thus very low. (2) A plasma channel is induced in a solid target by irradiation with a high power laser that creates a very intense shock wave. This mechanism conveys the acceleration of protons in the laser direction. The mechanisms must be tuned for the protons to reach a kinetic energy of 300–1200 keV where the pB11 fusion cross section is significantly large (note that this value is not a temperature). (3) Those ultra-fast protons enter the background plasma and collide with boron11 to produce three alphas. Fusion born alphas collide with protons of the plasma and accelerate them causing a chain reaction. (4) A combination of an induction current and a magnetic bottle keeps the chain reaction process going on, for a pulse long enough to get a high energy gain. (5) Materials for the background plasma and the laser target must be replaced for starting a new chain reaction cycle.

In the paper, relativistic self-focusing in the interaction of laser beam and plasma with periodical density ripple has been studied by the applied WKB approximation and higher-order paraxial theory. The result shows that under the influence of relativistic nonlinear effect, the dielectric function shows the fierce oscillational variation with similar periodicity, which then leads to the intense relativistic beam self-focusing along the propagation distance, such self-focusing also presents similar periodic variation. Besides, in the plasma with periodical density ripple, the initial density and the density ripple amplitude have obvious influence on self-focusing. When the two factors increase, then there will be more strength self-focusing. Choosing the appropriate initial density and the periodic density parameter is benefit to the formation of the more stable self-focusing.