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"Relativistic magneto-active laser plasmas"

V.S. Belyaev, A.P. Matafonov (CRIMB, Korolev, Russian Federation)



Results of experimental investigations:

Laser facility Neodymium. Its power is of 10 TW, the radiation intensity is up to 3´1018 W/cm2, the pulse duration is 1.5 ps, the wavelength is 1.055 mm. The facility is provided with a complex for measurements and control of parameters of laser radiation and diagnostic of atomic and nuclear processes in laser plasmas (parameters of x-ray, g-radiation, yields of neutrons and charged particles).

Generation of super-strong magnetic fields. We suggested and checked experimentally the direct spectral method for measurements of values of super-strong magnetic fields generated in laser plasmas. This method is based on the observation of resonance interaction between the Landau levels in magnetic field and energy levels of plasma ions. The value of the magnetic field is of about 40 MG at the laser intensity of 2´1017 W/cm2 and of about 60 MG at the laser intensity of 3´1017 W/cm2. The approach for control of generation of super-strong magnetic fields in laser plasmas has been checked using the method of interferometry of chirped laser pulses.

The effective temperature and the directed motion of fast atomic ions in laser picosecond plasmas. Results are based on the measurements of the Doppler spectra of fluorine hydrogenlike ions (the target is the plates from fluoride plastics with the thickness of 200 mm). The important peculiarity of the energy distribution of fast ions is their slow decreasing up to the energy of 1.4 MeV at the laser intensity of 2´1018 W/cm2; the effective temperature of fast ions is of the order of 350 keV. The directed motion of fast ions inside the target has been observed using red shift of the Doppler profile of the Lya line.

Generation of MeV-energy g-quanta. The photo-nuclear reactions 9(g, n)2a with the threshold energy of 1.67 MeV as well as 18 (g, n)180 with the threshold energy of 7.56 MeV have been used for investigation of generation of MeV-energy g-quanta. Accordingly, we observed the generation of 108 g-quanta with the energy higher than 1.67 MeV, and 103 g-quanta with the energy higher than 7.56 MeV.

The neutron-less fusion reaction 11 (p,a)2a. For the first time the yield of alpha-particles in neutron-less fusion reaction 11+p in laser plasmas has been observed. The yield of a-particles was of 103 particles per laser pulse. We found also the energy spectrum of a-particles which contains the maxima at the energies of 3-4 MeV and 6-10 MeV. We did not observe neutrons at simultaneous registration.

Investigation of the fusion reactions based on the perspective nuclear fuels DD, D6Li, D3He, H7Li. Results are presented for detailed investigation of the fusion reaction D(d,n)3He in laser picosecond plasmas. Both solid targets (r1 g/cm3) (CD2)n, BeD, TiD, and foam targets (r=0,01¸0,05 g/cm3) (CD2)n had been used. We measured the dependence of the neutron yield on the p- or s-polarization of laser radiation and on the laser contrast in various temporal ranges between 1 ps and 10 ns. The perspective fusion reactions 6Li(d,a)4He, 3He(d,p)4He, and 7Li(p,a)4He were investigated in our experiments.

We measured the energy spectra of a-particles and protons, containing the peaks: 1) at the energy of 11 MeV for the fusion reaction 6Li(d, a)4He, 2) at the energy of 9 MeV for the fusion reaction 7Li(p,a)4He , 3) at the proton energy of 3.7 MeV for the fusion reaction 3He(d,p)4, and 4) at the proton energy of 14.7 MeV for the fusion reaction 3He(d,p)4.

Generation of fast protons. The nuclear exchange reaction 7Li(p,n)7Be with the threshold energy of 1.88 MeV has been used for investigation of generation of fast protons. It was shown that of about 108 fast protons are produced in laser plasma with the energy higher than the threshold energy.

Investigation of energy spectra of fast protons. It follows from obtained energy spectra that the proton beams observed by CR-39 detectors which are placed behind the target exceed significantly the proton beams observed before the target (i.e. irradiated oppositely the laser beam). The maximum proton beam with the energy in the range of 0.8 ¸ 2.5 MeV was of 109 per one steradian and per one shot of laser pulse. The anisotropy in the proton yield disappears at the decreasing of the laser intensity up to 5´1017 W/cm2; the protons beam diminished up to 103 per steradian.

Investigation of spatial and angular distribution of fast protons. We considered the targets from Ti and Cu foils with the thickness of 25 and 30 mm. It was shown that the divergence angle for protons ejected forward normal to the rear side of the target is j1/2=260 for Ti foil, and j1/2=140 for Cu foil. The ring structures can be seen on CR-39 detectors; they are produced by proton beams with the energy less than 2.5 MeV. Protons with the energy higher than 2.5 MeV present narrow collimated beam with the divergence angle of j1/2 = 3. Inside this narrow collimated beam with the divergence angle j1/2 = 3 we observed well collimated proton beams with the divergence angle of j1/2 = 0.1¸0.3.

Results of our theoretical investigations:

The similarity of laser relativistic plasmas to astrophysical plasmas has been investigated in frames of magnetic hydrodynamics. The similarity criteria of these physical objects was determined. It was shown that relativistic laser intensity (> 1018 W/cm2) provides principal new mechanisms of energy transformation in laser plasma. Among them super strong quasi-stationary magnetic fields generation, production of electron-ion vortex structures.

It has been shown that the lifetime of such structures may be more (> 100 times) then laser pulse duration. Magnetic field pinching in these structures result in high (> 100 keV) plasma (ion) temperature.

The spatial structure of the electron vortexes and related magnetic fields produced in laser plasmas has been investigated. Qualitative similarity of potential vortexes in classical hydrodynamics with the electron vortex structures occurs. Mechanisms of acceleration of charged particles have been investigated which are related with the above considered structure of the quasi-stationary electromagnetic fields generated in laser plasmas. The betatron and cyclotron resonance acceleration mechanisms of electron acceleration have been investigated.

The model for the generation of high-energy ion (proton) beams with very small divergence angles has been suggested and investigated.

The obtained results indicate its possibilities and perspective for thermonuclear research. The presented results of experiments at 3´1018 W/cm2 intensity favour the obtained theoretical conclusions.

The obtained theoretical results are in good agreement with results of our recent experiments.

It is established that magneto-hydrodynamic processes in laser produced plasma realized in the conditions of huge magnetic fields on micro scale are similar of magneto-hydrodynamic processes observed in weak magnetic fields on cosmic scale.

The possibilities and perspectives of laser laboratory astrophysics as new quickly progressing scientific direction was shown.