Abstract
Experimental and simulation data [Moreau et al., Plasma Phys. Control. Fusion 62, 014013 (2019); Kaymak et al., Phys. Rev. Lett. 117, 035004 (2016)] indicate that self-generated magnetic fields play an important role in enhancing the flux and energy of relativistic electrons accelerated by ultra-intense laser pulse irradiation with nanostructured arrays. A fully relativistic analytical model for the generation of the magnetic field based on electron magneto-hydrodynamic description is presented here. The analytical model shows that this self-generated magnetic field originates in the nonparallel density gradient and fast electron current at the interfaces of a nanolayered target. A general formula for the self-generated magnetic field is found, which closely agrees with the simulation scaling over the relevant intensity range. The result is beneficial to the experimental designs for the interaction of the laser pulse with the nanostructured arrays to improve laser-to-electron energy coupling and the quality of forward hot electrons.
Highlights
The interaction of relativistically intense laser pulses with solid targets has stimulated considerable interest because of its practical applications in laser-driven particle acceleration[1,2,3,4,5,6,7], high-brightness ultrafast hard X-ray and Kα source[8,9,10,11], cancer treatment[12, 13], fast ignition in inertial confinement fusion[14], etc
We found that with the same plasma density gradient near the nanolayer interfaces (y = ±0.3 μm), the maximum intensity of the self-generated magnetic field increases as the fast electron current density increases
We have established accurate results for the generation of magnetic fields in a laser irradiated nanolayered target based on the electron magneto-hydrodynamic (EMHD) approximation
Summary
The interaction of relativistically intense laser pulses with solid targets has stimulated considerable interest because of its practical applications in laser-driven particle acceleration[1,2,3,4,5,6,7], high-brightness ultrafast hard X-ray and Kα source[8,9,10,11], cancer treatment[12, 13], fast ignition in inertial confinement fusion[14], etc. Some experimental and simulation results[15,16,17,18,19,20,21,22,23,24,25] indicate that the interaction of the intense laser pulse with the subwavelength nanowire targets can significantly increase laser energy absorption and enhance the flux and energy of relativistic electrons compared to flat targets. During the interaction of the laser pulse with the nanolayered target, a large number of energetic electrons are accelerated by the laser pulse, resulting in the formation of a relativistic electron beam. Note that the returned thermal electrons are reflected by the sheath field at the interface of the nanolayered target while the relativistic electrons can spread inside the target with a divergence angle, resulting in a net current along the surface of the nanolayered structure. Quasi-static magnetic fields of the order of 100 MG can be produced inside the gaps between the nanolayers
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