Signatures of fluid and kinetic properties in the energy distributions of multicharged Ta ions from nanosecond-laser-heated plasma
Résumé
The energy distributions of tantalum ions produced in a nanosecond laser-heated plasma at 4×1015W/cm2 are experimentally and theoretically investigated. They are measured far from the target with an electrostatic spectrometer and charge collectors. Shadowgraphy and interferometry are used to characterize the plasma dynamics in the first nanoseconds of the plasma expansion for electron densities ranging from 1018 to 1020cm−3. The experimental data clearly show two components in the energy distributions which depend on the ion charge states. These components are discussed in light of fluid and kinetic descriptions of the expanding plasma. In particular, quantitative comparisons with calculations performed with three-dimensional hydrodynamic (Troll) and 1D3V particle-in cell-codes demonstrate that a double layer created at the plasma-vacuum interface plays a crucial role in the acceleration of the highest-charge-state ions at high energy.
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