Spatially resolved Kα spectra of two-structure plasmas in a vacuum spark

Abstract
Spatially resolved Fe Kα spectra in the wavelength range of 1.7–2.0 Å (FeII‐XXVI) and 1.91–1.95 Å (FeII‐XIX) are first observed in a single shot with low‐resolution Johansson and high‐resolution Johann type crystal spectrometers, respectively. The spectra show the evident proof that the vacuum spark plasma has two different structures. One is a thermalized point plasma (≲10 μm) with high temperature (Te ∼2 keV) and high density (ne ∼1021 cm3). The spectrum contains x‐ray lines from FeXXIII‐XXVI. The other is an extended plasma (∼3 mm) associated with nonthermal electrons, where the region of intense emission of Kα lines from FeIII‐XX shifts toward the cathode with the increase of the ionic charge.