V. S. Lisitsa

Effect of prepulses with various durations on the neutron yield in laser picosecond plasma

Experimental results on the effect of picosecond and nanosecond prepulses on the neutron yield in laser picosecond plasma on the surface of solid (CD2)n targets at a laser intensity of 1018 W/cm2 are presented. It is demonstrated that the picosecond (nanosecond) prepulse decreases the neutron yield at a laser prepulse intensity of higher than 1013 (1012) W/cm2. The estimates indicate three possible mechanisms for the realization of the observed effect: stimulated Mandelstam-Brillouin scattering of the main pulse by the preplasma, channels of the generation of fast ions, and their possible deceleration in the preplasma. The results of calculations are compared with the experimental data.

Excitation of promising nuclear fusion reactions in picosecond laser plasmas

The results of experiments devoted to studying the excitation of the promising nuclear fusion reactions 6Li(d, α)4He, 3He(d, p)4He, 11B(p, 3α), and 7Li(p, α)4He, along with the standard reaction D(d, n)3He, in picosecond laser plasmas are presented. For the first time, it was shown that these reactions may proceed at a moderate laser-radiation intensity of 2 × 1018 W/cm2, the respective yield being 2 × 103 to 105 per laser pulse. A brief survey of the main processes responsible for the generation of fast electrons and fast ions (protons) at the front surface of the target and for the excitation of nuclear fusion reactions is given. The calculated and experimental results on the yield from nuclear fusion reactions in picosecond laser plasmas are compared. The possibilities for optimizing the yield from the promising fusion reactions excited in femto- and picosecond laser plasmas are discussed.

Influence of the radiation of the plasma-focus current sheath on the implosion dynamics of condensed targets

Results are presented from experimental and theoretical studies of the influence of the radiation of the plasma-focus current sheath on the implosion dynamics of condensed targets. Radiative losses from the current sheath of a plasma focus in neon, argon, and hydrogen with a 2% admixture of Xe are calculated with allowance for the line, bremsstrahlung, and recombination radiation. It is shown that the temperature of the neon plasma (10–15 eV) is quite sufficient to evaporate Al2O3 grains of radii 10–20 μm. The use of neon as a working gas makes it possible to alter the cold-start condition in experiments on the implosion of foam liners.

Warm Dense Matter and Strongly Coupled Plasmas Created by Intense Heavy Ion Beams and XUV-Free Electron Laser: An Overview of Spectroscopic Methods

High density plasma physics, radiation emission/scattering and related atomic physics, spectroscopy and diagnostics are going to make large steps forward due to new experimental facilities providing beams of intense heavy ions and X/XUV free electron laser radiation. These facilities are currently being established at GSI-Darmstadt and DESY-Hamburg in Germany to access new and complementary parameter regimes for basic research which have never been obtained in laboratories so far: homogenous benchmark samples near solid density and temperatures from eV up to keV. This will provide important impact to many disciplines like astrophysics, atomic physics in dense environments, dense and strongly coupled plasma effects, radiation emission, equation of state. The spectroscopic analysis of the radiation emission plays a key role in this research to investigate the dynamics of electric fields in multi-particle coupled Coulomb systems and the modification of plasma statistics.

Polarization recombination as a new channel for recombination of free electrons on complex ions

A new channel for recombination of free electrons on multicharged ions with a complex core is under investigation. The channel is connected with a dynamic polarization of an ions core by the colliding electron which results in radiation of the core and capture of the electron. This new channel (called polarization recombination, PlR) is estimated in the frame of a statistical (Thomas-Fermi) model of the complex ion. It is shown that the contribution of PlR to the total recombination rates may be comparable to or exceed (by more than an order of magnitude) the standard contribution of radiative recombination.

Experimental investigations of fast-proton production in a picosecond laser plasma

Results of experimental investigations of fast-proton production in a laser plasma are presented for the case where the intensity of laser radiation at the targets is 2 × 1018 W/cm2. Three processes of fast-proton acceleration in laser plasma are investigated: (1) the acceleration of protons from the front surface toward the laser pulse, (ii) the acceleration of protons from the front surface of the target toward its interior, and (iii) the acceleration of protons from the rear foil surface in the outward direction. The activation procedure and CR-39 tracker detectors featuring a set of various-thickness aluminum filters were used to record fast protons. It turned out that the proton-acceleration process is the most efficient in the case of proton acceleration from the rear foil surface in the outward direction. Experimental results revealed that about Np = 107 protons of energy in the region Ep > 1.9 MeV that are accelerated from the target surface toward a laser ray, Np = 4× 107 protons of energy in the region Ep > 1.9 MeV that are accelerated fromthe front surface of the target toward its interior, and Np = 4×108 protons of energy in the region Ep > 1.9 MeV that are accelerated from the rear foil surface in the outward direction are generated at a laser-radiation intensity of 2 × 1018 W/cm2 at the surface of aluminum, copper, and titanium targets. Experimental investigations aimed at optimizing the process of proton acceleration from the rear surface of aluminum foils were performed by varying the foil thickness over the range between 1 and 100 µm. The results of these experiments showed that there is an optimum foil thickness of 10 µm, in which case protons of maximum energy 5 MeV are generated.

Neutron production in picosecond laser-generated plasma on a be target

Experimental data on neutron production in a plasma generated on a Be target by a picosecond laser of intensity 2 × 1018 W/cm2 are presented. In contrast to previous measurements, a Ta converter is not used in this study to generate γ rays. The neutron yield is equal to 2 × 103 over a solid angle of 4π steradians per laser pulse. A simultaneous measurement of the maximum energy of hard x rays gave Eγmax ∼ 6 MeV, the number of these photons being 5 × 108 over an angle of 4π steradians per laser pulse. The energy distributions of fast electrons and photons are estimated theoretically.

Effective temperature and the directional motion of fast ions in a picosecond laser plasma

Experimental data are reported on the generation of fast ions in a picosecond laser plasma at a laser-radiation intensity of 2 × 1018 W/cm2. The results are obtained by measuring the Doppler spectra of hydrogen-like fluorine ions. An important feature of the energy distribution of fast ions is a slow decrease up to an energy of 1.4 MeV. In addition, the directional motion of fast ions deep into a target is found due to the redshift of the Doppler profile of the Lyα line. The parameters of the energy distribution of the ions are theoretically estimated.

Plasma satellites of X-ray lines of ions in a picosecond laser plasma

We present the results of our measurements of the spectra for multicharged ions in a plasma produced by moderately intense (about 1017Wcm−2) picosecond laser pulses. They suggest the existence of intense plasma oscillations with a frequency appreciably lower than the frequency of the laser radiation. The observed spectrum for the plasma satellites of the Lyman Lyα doublet of the hydrogenic F IX ion in a dense plasma was modeled theoretically. The resulting doublet profile was shown to have a complex structure that depends non-trivially both on the plasma density and on the frequency and amplitude of the plasma oscillations. The positions of the satellites and their separations allowed them to be associated with intense electrostatic oscillations with an amplitude of (4–6)×108Vcm−1 and a frequency near (0.7–1)×1015s−1. Assuming the oscillation frequency to be determined by the strength of the magnetic field B generated in the plasma, we obtained an estimate of B that is in reasonable agreement with other measurements and estimates of this quantity. Our theoretical analysis allowed explanation of the emission spectra observed when flat fluoroplastic targets were heated by intense picosecond laser pulses.

Statistical model of radiation losses for heavy ions in plasmas

The new statistical approach for calculation of radiation processes with heavy multielectron ions in plasma is developed. The method consists in consideration of atomic structure as a condensed medium, characterized by the spectrum of elementary excitations with plasma frequency, determined by local atomic electron density. The radiation losses in this model are due to excitation of plasma type oscillations in atom under its collisions with plasma electrons and could be expressed in a universal statistical form for all sorts of multielectron ions. The calculations of radiation losses on tungsten ions are performed in the wide range of plasma temperature variation, typical for physics of high temperature plasma with magnetic confinement. It is shown that the universal statistical approach results are within the data scattering of current numerical codes. The proposed statistical method for description of collective excitations in complex atoms for calculations of plasma radiation losses is of general physical interest. It allows obtaining the necessary data faster with the lesser computational resources.