Plasmas were generated by 3 ns pulsed lasers at 1064 nm wavelength using intensities of about 1010 W/cm2 irradiating solid targets with a different composition. The ion emission was investigated with time-of-flight measurements giving information of the ion velocity, charge state generation, and ion energy distribution. Measurements use a coil to generate a magnetic field suitable to deflect ions toward a Faraday cup and/or a secondary electron multiplier.

Ion acceleration of the order of hundred eV per charge state, plasma temperature of the order of tens eV, charge states up to about 4+, and Boltzmann energy distributions were obtained in carbon, aluminum, and copper targets.

The presented results represent useful plasma characterization methods for many applications such as the new generation of laser ion sources, pulsed laser deposition techniques, and post ion acceleration systems.

]]>Inertial Confinement Fusion is a promising option to provide massive, clean, and affordable energy for mankind in the future. The present status of research and development is hindered by hydrodynamical instabilities occurring at the intense compression of the target fuel by energetic laser beams. A recent patent combines advances in two fields: Detonations in relativistic fluid dynamics (RFD) and radiative energy deposition by plasmonic nano-shells. The initial compression of the target pellet can be decreased, not to reach the Rayleigh–Taylor or other instabilities, and rapid volume ignition can be achieved by a final and more energetic laser pulse, which can be as short as the penetration time of the light across the pellet. The reflectivity of the target can be made negligible as in the present direct drive and indirect drive experiments, and the absorptivity can be increased by one or two orders of magnitude by plasmonic nano-shells embedded in the target fuel. Thus, higher ignition temperature and radiation dominated dynamics can be achieved with the limited initial compression. Here, we propose that a short final light pulse can heat the target so that most of the interior will reach the ignition temperature simultaneously based on the results of RFD. This makes the development of any kind of instability impossible, which would prevent complete ignition of the target.

]]>The paper presents an investigation on self-focusing of cosh-Gaussian (ChG) laser beam in a relativistic–ponderomotive non-uniform plasma. It is observed numerically that the selection of decentered parameter and initial beam radius determines the focusing/defocusing of ChG laser beam. For given value of these parameters, the plasma density ramp of suitable length can avoid defocusing and enhance focusing effect significantly. Focusing length and extent of focusing may also be controlled by varying slope of the ramp density. A comparison with Gaussian beam has also been attempted for optimized set of parameters. The results establish that ChG beam focuses earlier and sharper relative to Gaussian beam. We have setup the non-linear differential equation for the beam width parameter using Wentzel–Kramers–Brillouin and paraxial ray approximation and solved it numerically using Runge–Kutta method.

]]>The parameters of X-ray radiation and runaway electron beams (RAEBs) generated at long-pulse discharges in atmospheric-pressure air were investigated. In the experiments, high-voltage pulses with the rise times of 500 and 50 ns were applied to an interelectrode gap. The gap geometry provided non-uniform distribution of the electric field strength. It was founded that at the voltage pulse rise time of 500 ns and the maximum breakdown voltage Um for 1 cm-length gap, a duration [full width at half maximum (FWHM)] of a RAEB current pulse shrinks to 0.1 ns. A decrease in the breakdown voltage under conditions of a diffuse discharge leads to an increase in the FWHM duration of the electron beam current pulse up to several nanoseconds. It was shown that when the rise time of the voltage pulse is of 500 ns and the diffuse discharge occurs in the gap, the FWHM duration of the X-ray radiation pulse can reach ≈100 ns. It was established that at a pulse-periodic diffuse discharge fed by high-voltage pulses with the rise time of 50 ns, an energy of X-ray quanta and their number increase with increasing breakdown voltage. Wherein the parameter Um/pd is saved.

]]>Energy gain of electron beams in bubble regime of the laser wakefield accelerator can be optimized by improving the acceleration length, radial accelerating and focusing force, number of monoenergetic electrons trapped inside the bubble, and increasing dephasing length. In order to enlarge the dephasing length, the phase velocity of the plasma wave can be increased by optimizing the plasma density profile. We report the estimation of dephasing length using plasma density distribution with the flat and linear-upward profile using two-dimensional particle-in-cell simulations. The size of wakefield bubble depends on the plasma density. With a positive plasma density gradient, the size of bubble decreases. The front and trail part of wake bubble will have different phase velocity in plasma density gradient region. After density transition in constant density region, the bubble elongates and the velocity of the back part of the bubble increases so that the accelerated electron phase synchronizes with the phase of the plasma wave. In a result, the electron acceleration length enhances to improve the beam quality.

]]>In this paper, the intense laser heating of hydrogen pair-ion plasma with and without electron impurities through investigation of related nonlinear phenomena has been studied in detail, using a developed relativistic particle-in-cell simulation code. It is shown that the presence of electron impurities has an essential role in the behavior of nonlinear phenomena contributing to the laser absorption including phase mixing, wave breaking, and stimulated scatterings. The inclusion of electron into an initial pure hydrogen plasma not only causes the occurrence of stimulated scattering considerably but also leads to the faster phase-mixing and wave breaking of the excited electrostatic modes in the system. These nonlinear phenomena increase the laser absorption rate in several orders of magnitude via inclusion of the electrons into a pure hydrogen pair-ion plasma. Moreover, results show that the electrons involved in enough low-density hydrogen pair-ion plasma can be accelerated to the MeV energy range.

]]>The paper describes a technique for operative control of the high-intensity pulsed ion beam parameters. The time-of-flight diagnostics uses one high-speed Faraday cup sensor with magnetic cut-off of low-energy electrons. The technique makes it possible to determine the composition of the beam (the type of ions and the degree of ionization), the absolute values of the current density of ions and the energy spectrum for each type of ions with an error of <±10%. The technique was tested at different pulsed ion accelerators and ion diodes both with self-magnetic insulation (accelerating voltage of 200–250 kV, ion current density of 20–300 A/cm2) and external magnetic insulation of the electrons (400–500 kV, 200 A/cm2). The article presents a comparative analysis of two types of Faraday cups with magnetic cut-off of the electrons and with electric bias.

]]>Krypton Large Impulse Thruster (KLIMT) project was aimed at incremental development and optimization of a 0.5 kW-class plasma Hall Effect Thruster in which, as a propellant, krypton could be used. The final thermally stable version of the thruster (the third one) was tested in the Plasma Propulsion Satellites (PlaNS) laboratory in the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw as well as in the European Space Agency (ESA) propulsion laboratory in the European Space Research and Technology Centre (ESTEC).

During final measurement campaign, a wide spectrum of parameters was tested. The plasma potential, electron temperature, electron concentration, and electron energy probability function in the far-field plume of the thruster were measured with a single cylindrical Langmuir probe. Faraday probes were used for recording local values of ion current. Using several collectors in different locations and moving them on the surface of a sphere, the angular distribution of the expelled particles was reconstructed which was a local measure of beam divergence. Angular distribution of ion flux as measured with a central Faraday probe was parameterized with krypton mass flow rate, voltage, coil current ratio, and the cathode mass flow rate. Beam divergence measurements with Faraday probes as well as plasma parameters derived from Langmuir probe seem to be consistent with our understanding of the operating envelope. Obtained results will serve as a baseline in the design of plasma beam structure diagnostics system for the PlaNS laboratory.

]]>In the interaction of short-laser pulses with a solid density target, pre-plasma can play a major role in ion acceleration processes. So far, complete analysis of pre-plasma effect on the ion acceleration by ultra-short laser pulses in the radiation pressure acceleration (RPA) regime has been unknown. Then the effect of pre-plasma on the ion acceleration efficiency is analyzed by numerical results of the particle-in-cell simulation in the RPA regime. It is shown that, for long-laser pulses (τp > 50 fs), the presence of pre-plasma makes a destructive effect on ion acceleration while it may have a contributing effect for short-laser pulses (τp < 50 fs). Therefore, the 35 fs (20 fs) laser pulse can accelerate ions up to 40 MeV (55 eV), which is almost two (three) times larger in energy rather than use of a 100 fs pulse with the same pre-plasma scale length.

]]>A novel way for igniting small thermonuclear assemblies by inertial confinement is proposed, by replacing the positive mass of an imploding dense star with the negative mass in the reference frame of a rapidly rotating thermonuclear target. According to Einstein's general theory of relativity, this negative mass can be orders of magnitude larger than the positive mass density of a neutron star. This novel concept also replaces the Plutonium 239 “spark plugs” of large thermonuclear devices with a shell of natural uranium surrounding a target composed of DT or Li6D.

Unlike the ignition by a laser – or particle beam – induced spherical implosion, this configuration, similar to that of an imploding star is not only Rayleigh–Taylor stable, but it can be realized with intense relativistic electron or ion beams, with an energy of about 100 MJ, having a short range in the dense high Z natural uranium shell.

]]>We propose a scheme for terahertz (THz) radiation generation by non-linear mixing of two cosh-Gaussian laser beams in axially magnetized plasma with spatially periodic density ripple where electron-neutral collisions have been taken into account. The laser beams exert a non-linear ponderomotive force due to spatial non-uniformity in the intensity. The plasma electrons acquire non-linear oscillatory velocity under the influence of ponderomotive force. This oscillatory velocity couples with preformed density ripples (n′ = n0αeiαz) to generate a strong transient non-linear current that resonantly derives THz radiation of frequency ~ωh (upper hybrid frequency). Laser frequencies (ω1 and ω2) are chosen such that the beat frequency (ω) lies in the THz region. The periodicity of density ripple provides phase-matching conditions (ω = ω1 − ω2 and ) to transfer maximum momentum from laser to THz radiation. The axially applied external magnetic field can be utilized to enhance the non-linear coupling and control various parameters of generated THz wave. The effects of decentered parameters (b), collisional frequency (νen), and magnetic field strength (B0 = ωcm/e) are analyzed for strong THz radiation generation. Analytical results show that the amplitude of THz wave enhances with decentered parameters as well as with the magnitude of axially applied magnetic field. The THz amplitude is found to be highly sensitive to collision frequency.

]]>A nonparaxial investigation for propagation characteristics of q-Gaussian laser beam in rippled density plasma is studied by considering the relativistic nonlinearity. The field distribution in the medium is expressed in terms of q parameter and beam width parameter f. Nonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying approximation is solved in a modulated density profile. Analytical theory of self-focusing including higher order terms in the expansion of dielectric function up to fourth order is developed and the variation of beam width parameter f with the distance of propagation for different parameters is studied. One may note that increased value of density ripple, laser intensity and depth of modulation, increases self-focusing whereas a lower value of q shows strong self-focusing. A comparative study between paraxial and nonparaxial study has also conducted. This study is useful for research in high energy density physics.

]]>The paper gives graphical and analytical investigation of the effect of critical beam power on self-focusing of cosh-Gaussian laser beams in collisionless magnetized plasma under ponderomotive non-linearity. The standard Akhmanov's parabolic equation approach under Wentzel–Kramers–Brillouin (WKB) and paraxial approximations is employed to investigate the propagation of cosh-Gaussian laser beams in collisionless magnetized plasma. Especially, the concept of numerical intervals and turning points of critical beam power has evolved through graphical analysis of beam-width parameter differential equation of cosh-Gaussian laser beams. The results are discussed in the light of numerical intervals and turning points.

]]>The effect of magnetic field on the plasma parameters and surface modification of Cu-alloy has been investigated. For this purpose, we have employed Nd: YAG laser at various irradiances ranging from 1.9 to 5 GW/cm2 to irradiate Cu-alloy under 5 torr pressure of argon, neon, and helium. The evaluated values of excitation temperature (Texc) and electron number density (ne) of Cu-alloy plasma explored by laser-induced breakdown spectroscopy technique are higher in the presence of 1.1 Tesla magnetic field as compared with field-free case. It is true at all irradiances as well as under all environmental conditions. It is also found that trends of both Texc and ne are increasing with increasing laser irradiance from 1.9 to 4.4 GW/cm2. For the highest used irradiance 5 GW/cm2, the decrease in both parameters is observed. The analytically calculated values of thermal beta, directional beta, confinement radius, and diffusion time for laser-irradiated Cu-alloy plasma confirm the validity of magnetic confinement. Scanning electron microscope analysis is utilized to study the surface modifications of laser-irradiated Cu samples and reveals the formation of islands, craters, cones, and droplets. The finer-scale surface structures are grown in case of magnetic. It is also revealed Texc and ne play a substantial part in the growth of surface structures on Cu-alloy.

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