Nonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying envelope approximation is solved using variational approach. The basic nonlinear phenomena of relativistic and ponderomotive self-focusing in a plasma are taken into account. Self-focusing, self-phase modulation as well as self-trapping of dark hollow Gaussian beam is studied for higher orders of hollow Gaussian beam (n).

The load current multiplier concept (LCM) was suggested for improving the energy transfer efficiency from pulse power generators to loads. The concept was initially demonstrated at atmospheric pressure and dielectric insulation on a compact, 100 kA, microsecond capacitor bank. This paper reports on the LCM design criteria for mega-ampere vacuum pulse power when the LCM comprises a large-inductance magnetic flux extruder cavity without a magnetic core. The analytical and numerical design approach presented was experimentally validated on GIT12 mega-ampere inductive energy storage generator with a constant-inductance load. The LCM technique increased the peak load current from typically 4.6 MA at 1.87 µs on this generator, to 6.43 MA at 2.0 µs. The electromagnetic power into a ~10 nH load increased from 100 GW to 230 GW. This result is in good agreement with the presented numerical simulations and it corresponds to a 95% increase of the achievable magnetic pressure at 8 cm radius in the load. The compact, LCM hardware allows the GIT12 generator to operate more efficiently without modifying the stored energy or architecture. The demonstrated load power and energy increase using the LCM concept is of importance for further studies on power amplification in vacuum and high energy density physics.

This paper presents an investigation of the excitation of a Tera hertz (THz) radiation by nonlinear interaction of a circularly polarized high power laser beam and density ripple in collisionless magneto plasma. The ponderomotive force due to the nonlinear interaction between the laser and density ripple generates a nonlinear current at a difference frequency. If the appropriate phase matching conditions are satisfied and the frequency of the ripple is appropriate, then this difference frequency can be brought in the THz range. Filamentation (self focusing) of a circularly polarized beam propagating along the direction of ambient magnetic field in plasma is first investigated within paraxial ray approximation. The beam gets focused when the initial power of the laser beam is greater than its critical power. Resulting localized beam couples with the pre-existing density ripple to produce a nonlinear current driving the THz radiation. Analytical expressions for the beam width of the laser beam, electric vector of the THz wave have been obtained. By changing the strength of the magnetic field, one can enhance or suppress the THz emission. For typical laser beam and plasma parameters with the incident laser power flux = 1014 W/cm2, laser beam radius (r0) = 40 µm, laser frequency (ω0) = 1014 rad/s and plasma density (n0) = 3 × 1018 cm−3, normalized ripple density amplitude (μ) = 0.3, the produced THz emission can be at the level of Giga watt in power.

In contrast to the usual laser fusion scheme with spherical irradiation and very high compression and ignition of fuel, the alternative scheme with side-on ignition of uncompressed solid density of fuel (Chu) may lead to a solution by using the now available picosecond laser pulses with higher than petawatt power. A necessary condition is to use clean laser pulses with better than 108 contrast ratio for suppression of relativistic self-focusing. When updating the analysis of Chu for fusion of deuterium-tritium and proton-11B, one problem is that the correct use of the stopping power of the alpha particles had to be solved. Discrepancies are evaluated in view of the stopping power at the low temperature range of the plasmas where the change of the emitted bremsstrahlung is involved.

The irradiation of solids with high energy laser or particle beams has led to a deeper understanding of the relaxation processes inside the target material. However, a lot of open questions remain. In the present paper, we will examine the irradiation of the model system Xe23+ @ 93 MeV → SrTiO3 within the framework of the two-temperature-model and study the electron-phonon-coupling g and the electron diffusivity De as well as the lattice diffusivity Dp. These are crucial parameters for which no experimental data is available. Experimentally, g is very difficult to measure and therefore theoretical predictions are of great importance. With the approach presented here it is possible to determine the coupling-constant by one order of magnitude.

Experimental results obtained with “Kanal-2” facility under the study of powerful laser pulse interaction with the low density microstructure media are presented and discussed in this paper. Forward scattering, back scattering, and transmission of laser radiation by aerogel foil plasma have been investigated. The temporal, spectral, and energy characteristics of both the radiation scattering in the direction of heating radiation beam and the back scattering radiation were studied; the directional diagrams of forward and back scattering radiation were obtained for ω0 and 2ω0 frequencies. Analysis of intensity redistribution on the heating beam cross-section after passing through a polymer microstructure target was carried out.

In this paper we present a newly developed one-dimensional hydrodynamic simulation code and use it to determine the shock evolution in flyer plate impact experiments. The code is Lagrangian with artificial viscosity and uses shock Hugoniot data in its equation-of-state calculations instead of SESAME data tables. First shock calculations for transparent targets show a good agreement with theoretical predictions, making the code suitable for designing future flyer impact experiments at the Nevada Terawatt Facility.

The nonlinear parabolic partial differential equation governing the evolution of the complex envelope in the slowly varying envelope approximation is solved using the variational approach. The basic nonlinear phenomena of relativistic and ponderomotive self-focusing in a plasma channel are taken into account. Self-focusing, self-phase modulation as well as self-trapping of laser beam is studied in a variety of situations. Further, in the absence of dissipation mechanisms, the stability of the beam is also studied.

The paper is devoted to the study of plasma effects, which are present in laser ablation at relatively high intensity (I ≥ 1012 W/cm2). We start from the classical “two temperature model” of laser ablation (“cold solid approximation”) and we extend it to higher intensities where laser-induced heating and laser-induced changes in the background material become relevant. The new model is also compared to experimental results on laser ablation of solid targets from short pulse lasers at high intensities (up to 1014 W/cm2). Finally, we consider the effects on laser-ablation of laser-generated fast electrons.

The remaining challenges, confronting the limited output peak power level of high-power microwave (HPM) sources, stimulate the development of power combining system. This paper reports the design methods and numerical results for a kind of dual-band incoherent power combining architecture applied in HPM. It is particularly effective to radiate dual-band microwave simultaneously, generated by a coaxial dual-band HPM source or two separate HPM sources of different bands. Two types of mode conversion structures, i.e., a dual-band feed line with co-aligned ports and a dual-band feed line with off-aligned ports, are proposed, where coaxial output port itself is adopted to connect the coaxial dual-band horn feed. These two types of feed lines provide a high conversion efficiency of about 98% from TEM or TM01 mode to TE11 mode and a bandwidth of about 10% at each band. The horn feed, with a high power handling capacity, is compact, and a good far-field radiation pattern at each band has been achieved by combining horizontal and vertical corrugations. Thus, the dual-band radiation system has not only realized incoherent power combination, with higher output peak power level, but also is suitable for feeding of, e.g., offset shaped single-reflector antennas in dual-band HPM systems in the future.

The present study deals with the propagation of short laser pulses in a parabolic plasma channel. A variational technique is used to obtain simultaneous evolution equations describing the laser pulse length and spot size in the presence of relativistic and ponderomotive nonlinearities. The effect of wakefields (inside the pulse) on the propagation characteristics of the laser beam is studied. Numerical methods are used to graphically analyze the evolution of the laser pulse length and intensity.

Technique of a linear transformer allows now to build the generators of high power nanosecond pulses with the current rise time of ~100 ns without intermediate power compression stages. This technique is being examined for use in high current high voltage pulsed accelerators. Plasma-filled diode has several advantages over standard vacuum diode that allow to improve the accelerators parameters. In this paper, plasma-filled diode experiments are described on generation of e-beam in the linear transformer accelerator. Possibility of use in the diode of isolated parallel plasma channels has been proven for the e-beam generation with cross-sectional area up to 50 cm2. The beam with current of 100 kA at voltage more than 400 kV was generated in the plasma-filled diode. Energy transmission efficiency from primary storage into a beam is about 54%.

The electric field intensity distribution and the phase velocity distribution of a slit in laser beams with different parameters are analyzed. Using three-dimensional test particle simulation, the laser beam with a slit induced acceleration of electrons with different initial momenta is investigated. Contrary to anticipation, the maximum net energy gain is not monotone increasing as the incoming momentum increasing. Based on the field structure and analysis, we gave an explanation for this.

Effect of intensity profile of the ablating laser on the dynamics of laser-blow-off (LBO) plume has been studied by fast imaging technique. This work emphasizes the geometrical aspect of the LBO plume, which is an important parameter for various applications. Visualization of the expanding plume reveals that geometrical shape and directionality (divergence) of the plume are highly dependent on the laser intensity profile. Present results demonstrate that the Gaussian profile laser produces a well-collimated, low divergence plasma plume as compared to the plume formed by a top-hat profile laser. The sequence of film removal processes is invoked to explain the role of energy density profile of the ablating laser in LBO mechanism.

We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (~50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars.

K-shell emission from copper target was observed by focusing femtosecond laser pulses very close to the target surface-air interface. It was shown that mechanism of X-ray emission is connected with generation of fast electrons in the air plasma area. Experiments demonstrated that moderate intensity of laser radiation (IL < 1015 W/cm2) was enough to produce considerable flux of X-ray photons of at least 10 keV energy. The parameters of generated X-ray emission were studied. It was found that after propagation through 40 cm thick air layer X-ray spectra consisted of pronounced Kα and Kβ characteristic lines and relatively small Bremsstrahlung continuum. Since transversal source size has an order of a few tens of micrometers, such a source can be used for absorption imaging of micro-objects in standard laboratory conditions. That can be particularly important for diagnostic of medical and biological samples in vivo.

It is proposed that single attosecond pulses be generated via electron's Thomson scattering of two counter-propagating laser pulses. In the case of linear polarization, the generation of a single attosecond pulse is highly sensitive to the carrier envelope phase (CEP). However, in the case of circular polarization, it is completely independent on the CEP, which will make circular polarization favorable to generate a stable attosecond X-ray pulse. For either linear or circular polarization, the radiation obtained by using two counter-propagating pulses can be much more intense than that obtained by only using one of these two pulses.

The effects of coherently enhanced radiation reaction on the motion of subwavelength electron bunches in interaction with intense laser pulses are analyzed. The radiation reaction force behaves as a radiation pressure in the laser beam direction, combined with a viscous force in the perpendicular direction. Due to Coulomb expansion of the electron bunch, coherent radiation reaction takes effect only in the initial stage of the laser-bunch interaction while the bunch is still smaller than the wavelength. It is shown that this initial stage can have observable effects on the trajectory of the bunch. By scaling the system to larger bunch charges, the radiation reaction effects are strongly increased. On the basis of the usual equation of motion, this increase is shown to be such that radiation reaction may suppress the radial instability normally found in ponderomotive acceleration schemes, thereby enabling the full potential of laser-vacuum electron bunch acceleration to GeV energies. However, the applicability of the used equation of motion still needs to be validated experimentally, which becomes possible using the presented experimental scheme.