Departures from thermal equilibrium in a dense Z‐pinch plasma

This paper presents on analysis of several features of the emission spectrum obtained from a dense hydrogen Z‐pinch plasma. The spectrum is characterized by an extremely broad Hβ line and by the absence of an emission line at the Hα wavelength. Comparison with theory shows that the spectrum is inconsistent with the assumption of a thermal or collision‐dominated plasma. The assumption of a substantial overpopulation of the atomic‐hydrogen excited levels, ascribed to a rising degree of plasma ionization, provides a satisfactory description of the observed spectrum. This result illustrates the difficulty of establishing valid equilibrium criteria for transient plasmas, even in the case of plasma densities as high as 10¹⁹ cm^-3.