Using fast imaging technique, the effect of transverse magnetic field on the shape and dynamics of the lithium plasma plume has been studied. Enhancement in the overall emission intensity as well as appearance of distinct structures (lobes) in the plasma plume in the presence of magnetic field has been observed. By introducing a variable magnetic field, the influence of J × B force in expanding plasma plume across the transverse magnetic field has been explored. It appears that J × B force does not has a substantial role in the observed structures in the present case rather different atomic processes, which get affected due to change in plasma parameters, are responsible for appearance of these structures.

In addition to the matured “laser inertial fusion energy” with spherical compression and thermal ignition of deuterium-tritium (DT), a very new alternative for the fast ignition scheme may have now been opened by using side-on block ignition aiming beyond the DT-fusion with igniting the neutron-free reaction of proton-boron-11 (p-11B). Measurements with laser pulses of terawatt power and ps duration led to the discovery of an anomaly of interaction, if the prepulses are cut off by a factor 108 (contrast ratio) to avoid relativistic self focusing in agreement with preceding computations. Applying this to petawatt (PW) pulses for Bobin-Chu conditions of side-on ignition of solid fusion fuel results after several improvements in energy gains of 10,000. This is in contrast to the impossible laser-ignition of p-11B by the usual spherical compression and thermal ignition. The side-on ignition is less than ten times only more difficult than for DT ignition. This is essentially based on the instant and direct conversion the optical laser energy by the nonlinear force into extremely high plasma acceleration. Genuine two-fluid hydrodynamic computations for DT are presented showing details how ps laser pulses generate a fusion flame in solid state density with an increase of the density in the thin flame region. Densities four times higher are produced automatically confirming a Rankine-Hugoniot shock wave process with an increasing thickness of the shock up to the nanosecond range and a shock velocity of 1500 km/s which is characteristic for these reactions.

A theoretical formalism is developed to obtain the mode structure of right circularly polarized nonlinear laser Eigen mode in a self created plasma channel in the presence of an axial magnetic field. The nonlinearity in electron response arises due to relativistic mass effect and ponderomotive force induced density redistribution. The Eigen mode is seen to be unstable to stimulated Raman backscattering involving an electrostatic quasi-mode and a scattered electromagnetic wave. The growth rate increases with ambient magnetic field.

Particle beams with uniform and well-confined intensity distributions are desirable in some high power beam applications to prolong the target lifetime or to improve the beam utilization. Three kinds of elements had been proposed for the beam homogenizing, such as octupole, pole-piece magnet, and step-like nonlinear magnets. In this paper, the new type of elements called heteromorphic quadrupole and focus sextupole are proposed. The Gaussian-like multiparticle beam redistribution by the octupole, heteromophic quadrupole, step-like nonlinear magnets, and focus sextupole has been simulated by the POISSON and LEADS code. The best redistribution result is obtained by the focus sextupole, and one of the solutions of redistributing beam with big halo can be that of using the focus sextupole and the heteromorphic quadrupole.

Recent heavy ion fusion target studies show that it is possible to achieve ignition with direct drive and energy gain larger than 100 at 1 MJ. To realize these advanced, high-gain schemes based on direct drive, it is necessary to develop a reliable beam smoothing technique to mitigate instabilities and facilitate uniform deposition on the target. The dynamics of the beam centroid can be explored as a possible beam smoothing technique to achieve a uniform illumination over a suitably chosen region of the target. The basic idea of this technique is to induce an oscillatory motion of the centroid for each transverse slice of the beam in such a way that the centroids of different slices strike different locations on the target. The centroid dynamics is controlled by a set of biased electrical plates called “wobblers.” Using a model based on moments of the Vlasov-Maxwell equations, we show that the wobbler deflection force acts only on the centroid motion, and that the envelope dynamics are independent of the wobbler fields. If the conducting wall is far away from the beam, then the envelope dynamics and centroid dynamics are completely decoupled. This is a preferred situation for the beam wobbling technique, because the wobbler system can be designed to generate the desired centroid motion on the target without considering its effects on the envelope and emittance. A conceptual design of the wobbler system for a heavy ion fusion driver is briefly summarized.

Enhancement of Kα yield from a metal foil covered with metal rods of submicron sizes, with low aspect ratio, irradiated by a p-polarized femtosecond laser pulses of about 1017 W/cm2 intensity is demonstrated. Obtained relative increase in Kα X-ray line emission is explained with a model of vacuum heating of fast electrons.

Using particle-in-cell simulations, we investigated the effect of group velocity dispersion (GVD) and third order dispersion (TOD) in the laser pulse on high-order harmonic generation and laser absorption in overdense plasmas. A 1020 W/cm−2, 35-fs transform-limited Gaussian pulse was stretched to 160 fs through chirping. When including GVD alone, the temporal pulse shape remains symmetric and no difference was seen in the harmonic spectra for opposite signs of GVD. However, when adding TOD to GVD, the pulse is no longer symmetric and noticeable differences in harmonics intensity were observed for opposite signs of TOD. We show that the higher harmonic intensity obtained with positive TOD is connected with a steeper front edge of the pulse and the appearance of strong modulations in the harmonic spectrum. The chirp broadens and shifts the harmonics. Laser energy absorption is also mostly affected by the pulse shape. Simple estimates indicate that, in the main example considered in this paper, about half the laser energy absorption (10%) is due to vacuum heating.

A new direction for high-power microwave (HPM) development is to investigate devices capable of producing HPMs with a complicated spectrum. In recent years, some HPM sources with two stable and separate frequencies have been investigated theoretically and experimentally. However, many short-comings still exist in these devices. Especially, the beam-wave interaction efficiency and the output microwave power are low in such devices. This paper proposes a novel dual-frequency HPM generator based on transition radiation. In the device, the electromagnetic fields are localized near the resonator cavities in the form of standing waves, and thus the interference between the different HPM components with different frequencies is weak. Compared with the existing dual-frequency devices, the new structure allows high beam-wave interaction efficiency and high output microwave power. As indicated in particle-in-cell simulation, with an electron beam of 500 kV voltage and 15.0 kA current guided by a magnetic field of 0.8 Tesla, an average power of 1.60 GW with a total power conversion efficiency of 21.3% is obtained, and the frequencies are 1.53 GHz and 3.29 GHz, respectively. Power level between two HPMs is comparable. The simulation results verify the feasibility of the dual-frequency HPM generator.

Raman backward scattering is investigated in the interaction of linearly polarized ultra short laser pulse with a homogenous cold underdense magnetized plasma by taking into account the relativistic effect and the effect of nonlinearity up to third order. The plasma is embedded in a uniform magnetic field perpendicular to both of propagation direction and electric vector of the radiation field. Nonlinear wave equation is set up and differential equations, which model the instability, are derived. Using of the Fourier transformation, analytical solutions are obtained for a set of physically relevant initial conditions and the temporal growth rate of instability is calculated. Results are significantly different in comparison with lower order computations. The growth rate of backward Raman scattering shows an increase due to the presence of external magnetic field as well as nonlinear effects.

The Rayleigh-Taylor instability is a key process in many fields of Physics ranging from astrophysics to inertial confinement fusion. It is usually analyzed deriving the linearized fluid equations, but the physics behind the instability is not always clear. Recent works on this instability allow for an very intuitive understanding of the phenomenon and for a straightforward calculation of the linear growth rate. In this Letter, it is shown that the same reasoning allows for a direct derivation of the relativistic expression of the linear growth rate for an incompressible fluid.

We present a method to determine where the nanoparticles nucleate and grow during pulsed laser deposition in an ambient gas. Briefly, nanocrystalline Si films are systemically deposited on the substrates located at a distance from the plasma and placed in horizontal direction; meanwhile an external electric field is introduced perpendicularly to the plume. Based on the transportation dynamics of Si nanoparticles corresponding to different electric fields, the lateral nucleation range of 0.1 to 33.8 mm is determined for Si nanoparticles deposited in 10 Pa Ar gas at a laser fluence of 4 J/cm2. Further simulation of the mass and area density of Si nanoparticles demonstrates that both nucleation and growth probabilities in nucleation region are approximately Gauss-dependent of the lateral distance.

This paper deals with the analytical study of the effect of chirping of a laser pulse on its intensity profile, as it propagates in plasma. Considering a matched laser beam, graphical analysis of the intensity distribution across the chirped laser pulse and growth of modulation instability has been presented. Further, considering finite pulse effects to be a perturbation, the growth rate of modulation instability of the chirped laser pulse is evaluated and compared with that obtained due to an unchirped pulse.

Time-of-flight spectra of C, Fe, and Si ions produced with the use of a KrF excimer laser have been analyzed. Ion currents were collected by Faraday cups and their responses were analyzed using a detector signal function. This function was derived from shifted Maxwell-Boltzmann velocity distribution, in order to uncover the contribution of partial currents of all the ionized species constituting the expanding plasma plume. The deconvolution method allowed to estimate parameters of the plasma, such as the ion temperature and the center-of-mass velocities of expanding ionized species. Furthermore, the linear charge-state dependence of the center-of-mass velocity has revealed the contribution of hydrodynamic and electrostatic forces to the expansion velocity of the plasma. The nearly isotropic distribution of the center-of-mass velocity indicates that the shape of the plasma plume is determined mainly by the angular distribution of the ionization degree of ions.

We consider ion projectile slowing down at low velocity Vp < Vthe, target thermal electron velocity, in a strongly coupled and de-mixing H-He ionic mixture. It is investigated in terms of quasi-static and critical charge-charge structure factors. Non-polarizable as well as polarizable partially degenerate electron backgrounds are given attention. The low velocity ion slowing down turns negative in the presence of long wavelength and low frequency hydromodes, signaling a critical de-mixing. This process documents an energy transfer from target ion plasma to the incoming ion projectile.

X-ray emission from Xe30+ ions at 350–600 keV impacting on an Au target was investigated at the Heavy Ion Research Facility at Lanzhou. Characteristic X-rays of Xe ions at energy of about 1.65 keV were observed. This X-ray emission is induced by the decay of very high Rydberg states of Xe ions. It was also found that the yield of such characteristic X-rays is decreasing with increasing the projectile kinetic energy. Simultaneously, the yield of the characteristic Au X-rays from the M shell increases also. These phenomena are qualitatively analyzed with the classical Coulomb over the Barrier Mode (COBM) for highly charged ions interacting with solid state surfaces.

An anomalously strong increase of nuclear fusion gains for laser driven compression and thermal ignition of hydrogen-boron11 has been discovered from computations by using the latest results of Newins and Swain about details of a resonance maximum of the astrophysical S-function at 148 keV for the reaction cross-sections. Extensive computations based on volume ignition showed some usual improvements of the fusion gains. However, for a very narrow range of parameters, the increase of the gain was found to be higher by more than a factor 6. This is very unusual in all similar computations and is related to retrograde properties which were known for other parameter values. On top it is most important that the anomalous range is in the practically very interesting range for incorporation of laser pulse energies of few megajoules. The gains of up to 20 may be of interest for power generation in future by the high density fusion scheme.