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"Relativistic
magneto-active laser plasmas" V.S. Belyaev, A.P. Matafonov
(CRIMB, Korolev, Russian Federation) Abstract: 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 9Âå(g, n)2a with the threshold energy of 1.67 MeV as
well as 18Òà
(g, n)180Òà 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 11Â (p,a)2a. For the first time the yield
of alpha-particles in neutron-less fusion reaction 11Â+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
(r»1 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 ðåàêöèè, 3) at the proton energy of 3.7
MeV for the fusion reaction 3He(d,p)4Íå, and 4) at the proton energy of
14.7 MeV for the fusion reaction 3He(d,p)4Íå. · 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. |
