Effect of density gradients on the generation of a highly energetic and strongly collimated proton beam from a laser-irradiated Gaussian-shaped hydrogen microsphere

Abstract

An investigation is made on the influence of the sharpness of the density gradients on the generation of energetic protons in a radially Gaussian density profile of a spherical hydrogen plasma. It is possible to create such density gradients by impinging a solid density target with a secondary lower intensity pulse, which ionizes the target and explodes it to create an expanded plasma target of lower effective density for the high-intensity main pulse to hit on. The density gradients are scanned in the near-critical regime, and separate regimes of proton motion are identified based on the density sharpness. An intermediate-density gradient [[Formula: see text]] favors the generation of high energetic protons with narrow energy spectra that are emitted with better collimation from the target rear surface. Protons with energies exceeding 100 MeVs could be achieved using such modified plasma targets with circularly polarized lasers of peak intensities [Formula: see text] and peak energy [Formula: see text].

100 MeV protons from nanostructured hemispherical target using PIC simulations

“…Spherical targets of the dimension of the order of the laser spot size have been found to help in improving the laser energy absorption by the electrons and ions [14]. Simulation of spherical targets of tailored gaussian density gradient has shown the ability to produce monoenergetic bunches of proton that have resulted due to shock acceleration near the center of the spherical target [15]. Experimentally, isolated micron-sized spherical targets have been found to generate quasi-monoenergetic proton and heavier ion energy spectra [16].…”