Abstract
A dual ion species plasma expansion scheme from a novel target structure is introduced, in which a nanometer-thick layer of pure deuterium exists as a buffer species at the target-vacuum interface of a hydrogen plasma. Modeling shows that by controlling the deuterium layer thickness, a composite H^{+}/D^{+} ion beam can be produced by target normal sheath acceleration (TNSA), with an adjustable ratio of ion densities, as high energy proton acceleration is suppressed by the acceleration of a spectrally peaked deuteron beam. Particle in cell modeling shows that a (4.3±0.7) MeV per nucleon deuteron beam is accelerated, in a directional cone of half angle 9°. Experimentally, this was investigated using state of the art cryogenic targetry and a spectrally peaked deuteron beam of (3.4±0.7) MeV per nucleon was measured in a cone of half angle 7°-9°, while maintaining a significant TNSA proton component.
Highlights
A dual ion species plasma expansion scheme from a novel target structure is introduced, in which a nanometer-thick layer of pure deuterium exists as a buffer species at the target-vacuum interface of a hydrogen plasma
Modeling shows that by controlling the deuterium layer thickness, a composite Hþ=Dþ ion beam can be produced by target normal sheath acceleration (TNSA), with an adjustable ratio of ion densities, as high energy proton acceleration is suppressed by the acceleration of a spectrally peaked deuteron beam
This was investigated using state of the art cryogenic targetry and a spectrally peaked deuteron beam of ð3.4 Æ 0.7Þ MeV per nucleon was measured in a cone of half angle 7°–9°, while maintaining a significant TNSA proton component
Summary
The most widely investigated acceleration mechanism is target normal sheath acceleration [3] and the pertinent features of TNSA accelerated beams are reproduced by analytic plasma expansion models [4,5,6,7] These ion beams have an inherently broad, thermal energy distribution whereas many potential applications of these compact sources require some degree of spectral control. When ultrathin foils expand to the extent that relativistic induced transparency occurs, volumetric laser heating of electrons can provide a boost to the heavier ion expansion rate, which in turn modifies the lighter ions’ energy spectrum [19,20] and beam profile [21]. In each of these schemes, the expanding heavier ions strongly affect
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