V. S. Belyaev

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.

Rydberg transitions in the spectra of near-neon-like Cu and Zn ions in different laser-produced plasmas: observations and modeling

Abstract We present observations of high-n transitions in the spectra of neon-like Cu19+ and Zn20+ ions observed in a variety of laser-produced plasmas (LPPs). The spectra are recorded with spectral resolution λ/Δλ=3000–8000 from three different laser sources: a 15 ns -pulse length Nd:glass, a ps-pulse length Nd:glass, a 12 ns -pulse length XeCl laser. These spectral observations are used to classify the transitions in the 2p–nd and 2s–np Rydberg series of the Ne-like copper and zinc ions, and to derive their first and second ionization energies. The plasma X-ray emission is simulated with a steady-state collisional-radiative model that includes the effect of self-absorption on line intensities, and the effect of hot-electron populations on the ionization balance. These spectra, along with those in our other recent work, provide a comprehensive set of data that can be used to test the accuracy of atomic-structure calculations, and to demonstrate the importance of opacity and hot electron effects on high-n transitions.

Identification and precise measurements of the wavelengths of high-n transitions in N-, O-, and F-like Zn ions

We have observed spectra of highly charged zinc ions from a variety of laser-produced plasmas. High-precision measurements of transition wavelengths have been made in the range 6.7–8.6 A, with accuracies of ≈1 mA. Line identifications for high-n transitions (n ≤ 7) in the N-, O-, and F-like spectra of Zn XXIV, XXIII, XXII, respectively, are made by comparison with steady-state collisional–radiative models.

Neutron production in a picosecond laser plasma at a radiation intensity of 3×1017W/cm2

Neutron production as a result of the reaction 2H(d, n)3He in a picosecond laser plasma is reported. A considerable neutron yield of 5×104 per pulse is obtained for the first time in a picosecond laser plasma on the surface of a solid deuterated target at laser radiation intensity of 3×1017 W/cm2.

On the role of prepulses during solid target heating by picosecond laser pulses

X-ray emission spectra of the plasma created at the surface of magnesium, aluminum, copper, and zinc targets heated by 1-ps laser pulses with a peak power density of up to 1016 W/cm2 were measured. The effect of a picosecond prepulse on the spectra was studied for various power densities and intensity contrasts of the main laser pulse. It is established that the emission spectra of laser plasmas are weakly affected by a change from 105 to 107 in the main pulse contrast relative to the first prepulse. Variations in the parameters of emission from aluminum and magnesium plasmas were calculated using relative intensities and widths of the resonance lines of H-and He-like ions and their two-electron satellite peaks.

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.

Promising lines of investigations in the realms of laboratory astrophysics with the aid of powerful lasers

The results of work on choosing and substantiating promising lines of research in the realms of laboratory astrophysics with the aid of powerful lasers are presented. These lines of research are determined by the possibility of simulating, under laboratory conditions, problematic processes of presentday astrophysics, such as (i) the generation and evolution of electromagnetic fields in cosmic space and the role of magnetic fields there at various spatial scales; (ii) the mechanisms of formation and evolution of cosmic gamma-ray bursts and relativistic jets; (iii) plasma instabilities in cosmic space and astrophysical objects, plasma jets, and shock waves; (iv) supernova explosions and mechanisms of the explosion of supernovae featuring a collapsing core; (v) nuclear processes in astrophysical objects; (vi) cosmic rays and mechanisms of their production and acceleration to high energies; and (vii) astrophysical sources of x-ray radiation. It is shown that the use of existing powerful lasers characterized by an intensity in the range of 1018–1022 W/cm2 and a pulse duration of 0.1 to 1 ps and high-energy lasers characterized by an energy in excess of 1 kJ and a pulse duration of 1 to 10 ns makes it possible to perform investigations in laboratory astrophysics along all of the chosen promising lines. The results obtained by experimentally investigating laser plasma with the aid of the laser facility created at Central Research Institute of Machine Building (TsNIIMash) and characterized by a power level of 10 TW demonstrate the potential of such facilities for performing a number of experiments in the realms of laboratory astrophysics.

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.