Three-dimensional "particle in cell" simulations show that a quasistatic magnetic field can be generated in a plasma irradiated by a linearly polarized Laguerre-Gauss beam with a nonzero orbital angular momentum (OAM). Perturbative analysis of the electron dynamics in the low intensity limit and detailed numerical analysis predict a laser to electrons OAM transfer. Plasma electrons gain angular velocity thanks to the dephasing process induced by the combined action of the ponderomotive force and the laser induced-radial oscillation. Similar to the "direct laser acceleration," where Gaussian laser beams transmit part of its axial momentum to electrons, Laguerre-Gaussian beams transfer a part of their orbital angular momentum to electrons through the dephasing process.
The effect of energy transfer by laser-accelerated fast electrons on thermonuclear gain of a shock- ignited ICF target at the different power and duration of high-intensity part of the laser pulse (spike) responsible for igniting shock wave generation has been investigated on the basis of hydro-kinetic numerical simulations. The key result of these studies is that the fast-electron energy transfer is able to provide a great contribution to igniting shock wave pressure to maintain a high thermonuclear gain with a significant decrease in the energy of the igniting part of laser pulse. Calculations were performed for the 2nd harmonic Nd-laser pulse in order to justify shock-ignition experiments on MJ-class facility, which is under construction in Russia now. Spike energy conversion to fast electron energy and its temperature were selected in the ranges, which are discussed in the literature. It has been found that fast electrons with a temperature of 50-70 keV, whose energy contains 20-40% of spike energy, make so large contribution to the pressure of igniting shock wave that the gain factor retains its value of 70-80 with spike energy decrease by 1.5-2 times.
This work presents a general concept of an intense laser-driven source of strong electromagnetic waves, which can be used for obtaining powerful terahertz radiation with controlled polarization. It is shown that the irradiation of a solid target surface by short relativistic laser pulses at small angles provides the excitation of strong compact relativistic discharge current pulses, propagating in a certain direction. For elliptical targets, this current emits elliptically polarized electromagnetic radiation at a given frequency with the ellipticity and the spectra defined by the target geometry. The proposed setup allows reaching extreme THz intensities and provides easy control of the radiation parameters, making it attractive for various scientific and technological applications.
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