Measurements of planar target heating by an intense lithium ion beam

Abstract

The heating of a planar multilayer (CH-Au-Al-CH) foil target by an intense lithium ion beam is measured using time-integrated spectroscopy of $K$\ensuremath{\alpha} x-ray satellite emission from the Al layer. The time-resolved beam irradiance, kinetic energy, and focal spot size are simultaneously measured using lithium ions Rutherford scattered from the foil. The approximately 20 ns full width at half maximum, 10 MeV peak kinetic energy, Li${}^{3+}$ ion beam deposited up to 435 TW/g (\ifmmode\pm\else\textpm\fi{}30%) in the Al layer. The peak electron temperature reached in the Al layer is estimated to be 38--43 eV by comparing the relative emission intensities from the He-like and Li-like Al with collisional-radiative-equilibrium (CRE) calculations. The data are used to examine one-dimensional radiation-hydrodynamic simulations that calculate the target plasma temperature and density using the measured beam parameters as input. It was found that a detailed CRE treatment of the atomic level populations and the line transport is essential for accurate calculations of the radiation loss from the ion heated target. Simulations that include such a treatment embedded within the radiation-hydrodynamic calculations are in good agreement with the data, within the experimental uncertainties. The methods developed here for observation and analysis of $K$\ensuremath{\alpha} spectra provide a sensitive tool suitable for the more stringent examinations of intense ion beam-matter interaction models that will ultimately be required for light-ion driven fusion.