In this paper, suppression of a transverse proton divergence is focused by using a controlled electron cloud. When an intense short pulse laser illuminates a foil plasma target, first electrons are accelerated and they form a strong electrostatic field at the target surface, then ions are accelerated by the strong field. When a target has a hole at the opposite side of the laser illumination, an electron cloud is limited in transverse direction by a neutral plasma at the protuberant part. The proton beam is accelerated and also controlled by transverse shaped electron cloud, and consequently the transverse divergence of the proton beam is suppressed. In 2.5-dimensional particle-in-cell simulations, the transverse shape of the electron cloud is controlled well and the transverse proton beam divergence is suppressed successfully; the transverse emittance is improved by about 28% compared with that in a conventional slab target.

Fast electrons generated in ultra-intense laser interaction with a solid target can produce multi-MeV ions from laser-induced plasmas. These fast ions can have different applications ranging from ion implantation to nuclear reactions. The most important parameter is the efficiency of fast ion production. An analytical model and particle-in-cell simulations were employed to examine acceleration mechanisms that can provide an optimal plasma density distribution due to a laser prepulse. We considered the acceleration of ions leaving a plasma layer with different density gradients, from a step-like overdense plasma to an underdense plasma with a smooth density gradient. The effects of the plasma initial scale length and density on the ion acceleration were analysed, and we found that the optimal case should have some plasma parameters. It is shown that overdense plasmas provide a higher density of accelerated ion energy than underdense plasmas at intensities below 10 19 W cm −2 .

Electron ponderomotive acceleration in a vacuum by a short-pulsed laser of TEM~1, 0! ϩ TEM~0, 1! mode is studied in this paper using a 3-dimensional~3D! particle simulation. It was found that the laser can trap electrons in transverse and accelerate them with the longitudinal ponderomotive force at the same time. Through this electron trapping and acceleration scheme of TEM~1, 0! ϩ TEM~0, 1! mode laser, the electron bunch is confined well in transverse and compressed remarkably in longitudinal. Therefore, a high energy, high density, and low emittances electron bunch is generated. For example, the result shows that for a laser with intensity of a 0 ϭ eE 0 0mvc ϭ10, the laser spot size of w 0 ϭ 15l, and the laser pulse length of L z ϭ 10l, the maximum energy gain reaches 301 MeV and the average energy 57.7 MeV. The electron bunch transverse radius is about 350l and the longitudinal size about 20l. The property of this accelerated bunch is improved compared with that generated by the laser of TEM~0, 0! mode.

A 2.45 GHz electron cyclotron resonance proton ion source and a dual-lens low energy beam transporta) Rev. Sci. Instrum. 83, 02A329 (2012); Generation of ultraintense proton beams by multi-ps circularly polarized laser pulses for fast ignition-related applications Phys. Plasmas 18, 053108 (2011);

A suppression of a transverse divergence of high-energy protons generated by an interaction of a laser with a thin slab foil is investigated in this paper by 2.5-dimensional particle-in-cell simulations. When an intense (approximately 10(24) W/m(2)) short-pulse (a few ten femtoseconds) laser illuminates a thin foil target of a hydrogen, foil electrons are accelerated and compressed longitudinally by a laser light pressure and fast electron bunches are produced in the thin foil target. The fast electron bunches pass through the foil target, and a strong magnetic field is produced near the opposite side of the foil target. Because the strong magnetic field confines the electrons, a localization of the electrons is observed at the opposite side of a laser illumination surface. The local electron bunch produces not only a longitudinal electric field, but also a transverse electric field, which is directed toward the laser axis. Protons are accelerated and extracted from the foil, and the proton bunch divergence is successfully suppressed by the transverse electric field.