Radiation-Pressure Acceleration of Ion Beams from Nanofoil Targets: The Leaky Light-Sail Regime

A new ion radiation-pressure acceleration regime, the "leaky light sail," is proposed which uses sub-skin-depth nanometer foils irradiated by circularly polarized laser pulses. In the regime, the foil is partially transparent, continuously leaking electrons out along with the transmitted laser field. This feature can be exploited by a multispecies nanofoil configuration to stabilize the acceleration of the light ion component, supplementing the latter with an excess of electrons leaked from those associated with the heavy ions to avoid Coulomb explosion. It is shown by 2D particle-in-cell simulations that a monoenergetic proton beam with energy 18 MeV is produced by circularly polarized lasers at intensities of just 10(19) W/cm(2). 100 MeV proton beams are obtained by increasing the intensities to 2 x 10(20) W/cm(2).

Shock creation and particle acceleration driven by plasma expansion into a rarefied medium

The expansion of a dense plasma through a more rarefied ionized medium is a phenomenon of interest in various physics environments ranging from astrophysics to high energy density laser-matter laboratory experiments. Here this situation is modeled via a one-dimensional particle-in-cell simulation; a jump in the plasma density of a factor of 100 is introduced in the middle of an otherwise equally dense electron-proton plasma with an uniform proton and electron temperature of 10 eV and 1 keV, respectively. The diffusion of the dense plasma, through the rarefied one, triggers the onset of different nonlinear phenomena such as a strong ion-acoustic shock wave and a rarefaction wave. Secondary structures are detected, some of which are driven by a drift instability of the rarefaction wave. Efficient proton acceleration occurs ahead of the shock, bringing the maximum proton velocity up to 60 times the initial ion thermal speed. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3469762]

Carbon ion acceleration from thin foil targets irradiated by ultrahigh-contrast, ultraintense laser pulses

In this study, ion acceleration from thin planar target foils irradiated by ultrahigh-contrast (10(10)), ultrashort (50 fs) laser pulses focused to intensities of 7 x 10(20) W cm(-2) is investigated experimentally. Target normal sheath acceleration (TNSA) is found to be the dominant ion acceleration mechanism when the target thickness is >= 50 nm and laser pulses are linearly polarized. Under these conditions, irradiation at normal incidence is found to produce higher energy ions than oblique incidence at 35 degrees with respect to the target normal. Simulations using one-dimensional (1D) boosted and 2D particle-in-cell codes support the result, showing increased energy coupling efficiency to fast electrons for normal incidence. The effects of target composition and thickness on the acceleration of carbon ions are reported and compared to calculations using analytical models of ion acceleration.

Dependence of the ion energy on the parameters of the laser pulse and target in the radiation-pressure-dominated regime of acceleration

When the dominant mechanism for ion acceleration is the laser radiation pressure, the conversion efficiency of the laser energy into the energy of relativistic ions may be very high. Stability analysis of a thin plasma layer accelerated by the radiation pressure shows that Raleigh-Taylor instability may enhance plasma inhomogeneity. In the linear stage of instability, the plasma layer decays into separate bunches, which are accelerated by the radiation pressure similarly to clusters accelerated under the action of an electromagnetic wave. The energy and luminosity of an ion beam accelerated in the radiation-pressure-dominated regime are calculated.