Abstract
We have measured the x-ray emission, primarily from K(α),K(β), and He(α) lines, of elemental copper foil and "foam" targets irradiated with a mid-10(16) W/cm(2) laser pulse. The copper foam at 0.1 times solid density is observed to produce 50% greater He(α) line emission than copper foil, and the measured signal is well-fit by a sum of three synthetic spectra generated by the atomic physics code FLYCHK. Additionally, spectra from both targets reveal characteristic inner shell K(α) transitions from hot electron interaction with the bulk copper. However, only the larger-volume foam target produced significant K(β) radiation, confirming a lower bulk temperature in the higher volume sample.
Highlights
Laser irradiation of transition metals is often employed to produce characteristic x-rays for use in high-energy-density experiments
The energy of resonance line transitions is equal to the energy difference between initial and final states of a decaying electron, but in this case the atom is highly ionized, retaining only one, two, or a few electrons
Analysis of inner-shell and line-transition radiation can be used as diagnostics for distinct information regarding the plasma conditions in the experiment
Summary
Laser irradiation of transition metals is often employed to produce characteristic x-rays for use in high-energy-density experiments. These x-rays are produced in two relatively distinct processes, namely inner shell electronic transitions and ionic resonance line transitions. It has been suggested that low density solid “foam” targets may behave more like gaseous targets, yielding increased conversion efficiency while remaining simple to field.. It has been suggested that low density solid “foam” targets may behave more like gaseous targets, yielding increased conversion efficiency while remaining simple to field.7 To investigate this we performed an experiment using a 10% solid density copper (“foam”) target on the Omega EP laser, and compared this with a solid copper target (foil) under near-identical laser irradiation. We present the measured x-ray spectra from these targets and discuss the implications for the plasma conditions that generated these spectra
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