The spectroscopy of plasmas carrying sound waves. II. Spectral line profiles

This paper extends the theory, developed in an earlier paper on the intensities of spectral lines emitted by a plasma in which a sound wave is propagating, to a consideration of their profiles. The expression that is presented for the profiles is based on the assumption that the spectral lines are broadened and shifted by the combined Doppler effects of motion associated with the sound wave and with thermal motion. The treatment covers isothermal and adiabatic sound waves in two plasma conditions, namely, (1) uniform low-density plasma, and (2) low-density plasma of uniform pressure and having a temperature gradient. The results show that the profiles have a characteristic asymmetric shape and that for a sound wave propagating towards the observer the center of gravity of the profile is blueshifted although there is no net flow of plasma.