High gradients of electron temperature appear in plasma corona under direct laser irradiation of inertial confinement fusion targets. This results in nonlocality of heat transport. Such effect influence the efficiency of laser absorption, redistribute heat fluxes and could preheat plasma ahead the front shock wave, therefore alter the compression adiabat. Ignition requires a specially tuned compression dynamics, so such an effect should be taken into account. Target simulations with nonlocal models show the decrease of compression efficiency and hot-spot parameters degradation compared to local models: Spitzer–Härm model with and without flux-limiter.

The numerical results for cryogenic direct drive targets of megajoule facilities with radiation in the second and third harmonics of a Nd laser are presented. The calculations were performed with the 1D radiation hydrodynamics code ERA with the laser light absorption model that takes into account stimulated Brillouin scattering (SBS), generation of fast electrons in the processes of two-plasmon decay (TPD), and stimulated Raman scattering (SRS). The verification of the developed models was carried out on the basis of the comparison with experiments performed at the OMEGA and NIF facilities. The ignition margin (WQ) of nonuniform fusion targets with an allowance for energy losses due to radiation transfer and heat conduction from the hot spot was the objective of the target optimization. The calculations showed that SBS and target heating by fast electrons generated in TPD and SRS fatally reduce WQ of targets with a CH ablator for the megajoule laser with wavelength λ = 0.53 µm. The possibilities of decreasing these effects by replacing a CH ablator with a glass ablator and reducing the laser intensity upon increasing the target aspect ratio are considered. However, in both cases, WQ remains substantially below unity for the laser with wavelength λ = 0.53 µm. The ignition margin increases by a factor of ∼2 upon transition from the second to the third harmonic of a Nd laser. A glass ablator almost eliminates fast electrons in calculation with the laser wavelength λ = 0.35 µm. In this case, if SBS is reduced by a factor of 3–4 via shifting the laser emission lines in the neighboring channels by Δμ ≈ 10–20 Å, the ignition margin WQ ∼ 2 and a fusion energy yield of ∼50 MJ are obtained in the 1D calculation for a laser energy of ∼2 MJ and the third harmonic of a Nd laser.

The mechanism of stochastic electron acceleration and heating by a picosecond laser pulse in underdense plasma is studied using particle-in-cell simulations and theoretical models. The formation of wide electron energy spectra in the simultaneously acting laser and plasma fields is analyzed. It is shown that electron scattering by turbulent plasma fluctuations excited through stimulated forward Raman scattering plays a governing role in the formation of high-energy tails in the electron distribution function.

2D PIC code simulations have been performed for the optimization of gas jet target parameters to achieve a maximal energy and efficiency of charged particle acceleration in planned experiments at the 20 TW picosecond SOKOL-P laser. These calculations specify an opportunity to obtain energy up to Ee ∼ 200 MeV and efficiency ηe ∼ 10% for accelerated electrons and Ep ∼ 30 − 50 MeV and ηp ∼ 5% for accelerated protons in these experiments at laser intensity I ∼ 5 ⋅ 1019 W/cm2. They show the necessity of providing a formation of hydrogen jets with diameter ∼ 1mm, a gas molecule concentration ∼ 2 ⋅ 1019 cm−3 and steep density gradients ∼ 200 μm at the edge of the gas jet target for achieving these parameters of laser accelerated particle beams.

We outline the results of experiments in the generation of X-ray laser radiation on the 4d-4p Ni-like ion transitions at a wavelength lambda = 189 angstrom under sequential irradiation of plane targets by two laser pulses focused to a line. These experiments were executed on the Sokol-p picosecond laser facility. The average energy of a 4-ps long ultrashort pump pulse was equal to 6.5 J, the energy of a 0.44-ns long prepulse was equal to 2.7 J, and the time delay between them was equal to 1.5 ns. The effective gain for short target lengths was equal to similar to 24 cm(-1). In the travelling pump wave regime, which was realised using a ladder mirror, we obtained an 8-fold increase in output X-ray laser energy in comparison with the output energy obtained in the ordinary target irradiation regime.

Some thermonuclear X-ray bursters exhibit a high-frequency (about 300 Hz or more) brightness modulation at the rising phase of some bursts. These oscillations are explained by inhomogeneous heating of the surface layer on a rapidly rotating neutron star due to the finite propagation speed of thermonuclear burning. We suggest and substantiate a mechanism of this propagation that is consistent with experimental data. Initially, thermonuclear ignition occurs in a small region of the neutron star surface layer. The burning products rapidly rise and spread in the upper atmospheric layers due to turbulent convection. The accumulation of additional matter leads to matter compression and ignition at the bottom of the layer. This determines the propagation of the burning front. To substantiate this mechanism, we use the simplifying assumptions about a helium composition of the neutron star atmosphere and its initial adiabatic structure with a density of 1.75 × 108 g cm−3 at the bottom. 2D numerical simulations have been performed using a modified particle method in the adiabatic approximation.

Results from experimental studies of bremsstrahlung and characteristic radiation spectra from laser targets irradiated with ultrashort laser pulses with intensities of up to ∼1019 W/cm2 are presented. The continuous spectra of hard X-ray emission from Ta and Al targets and the line spectrum of copper were measured. The temperature of fast electrons was obtained from the measured hard X-ray spectra, and the Kα radiation yield from Ta was measured. The energy conversion efficiency of laser radiation into the copper characteristic radiation was obtained from the measured yield of Kα radiation.

Results from experimental studies of bremsstrahlung and characteristic radiation spectra from laser targets irradiated with ultrashort laser pulses with intensities of up to ∼10 19 W/cm 2 are presented. The continuous spectra of hard X-ray emission from Ta and Al targets and the line spectrum of copper were measured. The temperature of fast electrons was obtained from the measured hard X-ray spectra, and the K α radiation yield from Ta was measured. The energy conversion efficiency of laser radiation into the copper characteristic radiation was obtained from the measured yield of K α radiation.

The LegoLPI code was used for simulation of laser-driven proton acceleration with the purpose to find an optimal conditions for the generation of proton beams with parameters required for hadron therapy. The 2D PIC simulations were done for various type of targets (double-layer foils, polyethylene foils, hydrogen jets) and target irradiation conditions (different intensities and polarizations, laser pulse wavelengths and durations, focal spot sizes). It is shown that efficiency of proton generation would be high enough for the optimal condition of target irradiation, but the spectrum of accelerated protons is rather broad for both linearly and circularly polarized laser pulses because of the two-dimensional effects arising when the proton acceleration length is comparable with the focal spot. As follows from the 2D LegoLPI calculations, the efficiency of formation of proton spectrum in energy range of 200–250 MeV and normalized to laser energy may reach values (0.5–1)•107 protons•(MeV•J)−1 for the considered types of laser – targets systems. The performed calculations specify an opportunity of generation proton beams whose parameters meet proton therapy requirements with the use of a laser that would have a peak power of about 1 PW and average power up to 1 kW. The powerful ultra-short pulse lasers, which are under construction in some countries around the world, are very close to the facilities necessary for this purpose.

Results of experiments on proton acceleration from aluminum foils and organic films irradiated by laser pulses with intensities of up to 2 × 10 19 W/cm 2 are presented. To prevent thin targets from destruction by the superluminescence prepulse, a fast light shutter based on a Pockels cell was introduced in the amplifying system of the SOKOL-P facility. As a result, the energy contrast with respect to the superluminescence prepulse increased to 4 × 10 6 , which made it possible to carry out experiments on the irradiation of targets with thicknesses less than 100 nm. It is found that the target material insignificantly affects the yield of accelerated protons.

2D calculations of the promising laser hohlraums were performed with using of the Sinara computer code. These hohlraums are intended for achievement of indirectly-driven thermonuclear ignition at laser energy above 1 MJ. Two calculation variants of the laser assembly with the form close to a rugby ball were carried out: with laser entrance hole shields and without shields. Time dependent hohlraum radiation temperature and x-ray flux asymmetry on a target were obtained.

When femto-second pulse of Ti-Sa laser with 1021 W/cm2 intensity and 40 fs pulse duration interacts with 0.1 mum thickness aluminum foil, matter ionization is defined by electric field of the laser. The influence of field ionization on ion acceleration is studied with 2D hybrid code calculating fast particles by particle in cell method and thermal particles by approximation combining particle method and MHD approach. Results of the calculation are compared to the case, when plasma has initial state corresponding to temperature 100 eV. It is shown, that efficiency of energy transformation from laser field to electrons and ions is much higher when field ionization effect is taken into account. This leads to increasing of the depth of skin-layer and energy of electrons. Influence of Weibel instability development on magnetic field saturation and return current generation is studied. Calculations show that protons are accelerated due to the field of charge separation up to energies of 20-100 MeV in the case of field ionization that by an order exceeds the amount of ions in the case of initial plasma set.

The transient collisional excitation (TCE) scheme was used to obtain generation of X-ray laser radiation on the 3p-3s transitions of the Ne-like Ti-ions at 10 TW SOKOL-P laser developed at RFNC-VNIITF. The Nd-laser light was focused in a line with length from 2 up to 8 mm and width of 30 microns. Two successive pulses irradiated the polished Ti-slab. The duration of prepulse was equal to 400 ps and a pumping pulse had duration of 4 ps; the delay between pulses equals to 1.5 ns. The Nd-laser energy was about of 10 J and the ratio of energy in prepulse and basic pulses was equal to 1:2. The grating spectrometer equipped with a focusing mirror and CCD detector was used for measurement of the X-ray laser line at 32.6 nm. A small signal gain about of 30 cm-1 was obtained in experiments with target length from 2 up to 4 mm. The 32.6 nm line radiation with energy about of 1 ¼J and divergence of 9 mrad were registered in SOKOL-P experiments with target length of 8 mm.

Experimental results are presented for proton acceleration from the back of a target irradiated by laser pulses with intensities up to 2 × 10 19 W/cm 2 generated by the SOKOL-P facility. The proton acceleration efficiency increases with decreasing of the target thickness. However, thin targets are destroyed by the amplified spontaneous emission (ASE) prepulse before the main pulse arrival. An additional optical switch based on a Pockels cell has been used in the amplification section to carry out the experiments with ultrathin foils. As a result, the energy contrast with respect to the ASE prepulse has been increased up to 4 × 10 6 . Owing to high contrast, the experiments on studying proton acceleration from foils with thicknesses less than 100 nm have been carried out.