Soft-x-ray amplification in a capillary discharge

Soft-x-ray amplification in the C v i Balmer α transition is observed in a capillary discharge. The capillary is made of polyethylene with a bore diameter of 1.2 mm. A hot and dense carbon plasma which is formed on the capillary axis region expands radially and collides with the wall where it undergoes a rapid cooling and subsequent recombination. The amplification takes place in this cool (${\mathit{T}}_{\mathit{e}}$∼13 eV) plasma region, according to space-resolved spectral data obtained using a 2-m grazing incidence spectrograph. The gain coefficient is measured to be 2.8 ${\mathrm{cm}}^{\mathrm{-}1}$.