Density measurement in a vacuum-spark-discharge microplasma from the inner-shell excitation of satellite transitions

The electron density in the high-temperature microplasma region of a titanium vacuum spark discharge is measured from the relative intensities of the dielectronic satellites of the Ti xii resonance line. The triplet doubly excited levels $2s2p{}_{}{}^3{}_{}{}^{}P$ and ${2p}^2{}_{}{}^3{}_{}{}^{}P$ of Ti xii are populated primarily by inner-shell excitation due to energetic electron impact, and the resulting triplet satellite lines are enhanced relative to the singlet satellite lines. The measured electron density in the microplasma region is 1.5×${10}^{23}$ ${\mathrm{cm}}^{-3\mathrm{}}$. This represents an energy concentration of ${10}^8$ J ${\mathrm{cm}}^{-3\mathrm{}}$ and a plasma kinetic pressure of ${10}^9$ bars.