Computed circular polarization of line emissions for n=1 transitions between highly excited states of hydrogenic ions in tokamak plasmas

Circular polarization of spectral lines due to n=1 transitions between highly excited states (n=68) of low-Z hydrogenic ions (C vi and O viii) has been computed under tokamak plasma conditions. The numerical model includes relativistic corrections, the Zeeman effect, the motional Stark effect, and Doppler broadening. The motional Stark effect in spectral line profiles is negligible because of Doppler broadening. The Zeeman effect is described by the intensity-averaged splitting factor, which is equal to unity and independent of the Stark effect for all Rydberg lines (provided the n shells are well separated). The circular polarization of the line is proportional to the component of the magnetic field in the direction of the observation direction. An analytical expression for the polarization, as a function of the intensity-averaged Zeeman splitting and a characteristic linewidth, is formulated by fitting the numerical results obtained for a variety of plasma conditions and spectral lines.