Abstract
The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes to increase achievable ion energies and conversion efficiencies. Whilst the evolving nature of laser-plasma interactions can limit the effectiveness of individual acceleration mechanisms, it can also enable the development of hybrid schemes, allowing additional degrees of control on the properties of the resulting ion beam. Here we report on an experimental demonstration of efficient proton acceleration to energies exceeding 94 MeV via a hybrid scheme of radiation pressure-sheath acceleration in an ultrathin foil irradiated by a linearly polarised laser pulse. This occurs via a double-peaked electrostatic field structure, which, at an optimum foil thickness, is significantly enhanced by relativistic transparency and an associated jet of super-thermal electrons. The range of parameters over which this hybrid scenario occurs is discussed and implications for ion acceleration driven by next-generation, multi-petawatt laser facilities are explored.
Highlights
The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes to increase achievable ion energies and conversion efficiencies
The use of linearly polarised light is predicted to result in the formation of a dual-peaked electrostatic field, due to radiation pressure acceleration (RPA) at the target front and target normal sheath acceleration (TNSA) at the rear[17], and hybrid scenarios in which ions from both mechanisms combine[18]
Whereas ion acceleration is effective in ultrathin foils, such targets are subject to the onset of relativistic induced transparency (RIT)[19]
Summary
The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes to increase achievable ion energies and conversion efficiencies. We report on an experimental demonstration of efficient proton acceleration to energies exceeding 94 MeV via a hybrid scheme of radiation pressure-sheath acceleration in an ultrathin foil irradiated by a linearly polarised laser pulse This occurs via a double-peaked electrostatic field structure, which, at an optimum foil thickness, is significantly enhanced by relativistic transparency and an associated jet of super-thermal electrons. Difficulties in converting the inherent linearly polarised light to circular polarisation (due to the large diameter of the unfocused beam) means that linearly polarised-driven hybrid acceleration scenarios are highly likely to prevail These facilities are expected to produce focussed intensities up to 1023 W cm−2, which would render near-solid density foils relativistically transparent, increasing the role of RIT-enhanced processes
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