Spectral Line Emission from a Transient Nonuniform Plasma

Some effects of spatial gradients and transient behavior on spectral line radiation from impurities in a low-energy θ-pinch plasma are discussed for a case where local thermodynamic equilibrium could not be assumed. The plasma was produced and preheated by a fast capacitor bank discharge, a controlled trapped magnetic field was generated by a slower discharge through the same coil, and magnetic compression was achieved by a fast rising reverse magnetic field. Measured carbon impurity line intensities were compared to predictions on the basis of magnetohydrodynamic calculations coupled with spectroscopic theory. Large errors are incurred in electron temperatures from relative intensities of lines from successive stages of ionization if the radial variation of ionization and excitation is ignored.