Spectroscopic measurements on xenon plasma in a hollow cathode

Optical emission from xenon plasma in a hollow cathode has been recorded over a wide range of wavelengths extending from vacuum ultraviolet to the visible band 100-590 nm. The cathode was operated in direct current discharge mode with a continuous flow of xenon ~13 cc min -1 at 70 Torr. A column of neutral xenon gas (~21.2 cm long) existed in-between the active plasma column (~1 cm long) source and the detector. The observed spectra show that strong Xe II and impurity (Ba, Al and Ca) lines are superimposed on a weak continuum. Xenon I lines have not been observed. A subsidiary broadened continuum band within the far vacuum ultraviolet range 100-200 nm supports the evidence that the emission due to the transitions by the excited molecular dimer/excimer species is also involved. In the present work, bremsstrahlung emission has been used to estimate the plasma electron temperature Te = 1.1 eV. The resulting electron density ne = 1014 cm-3 is then obtained using the Saha formulation for the ratio of the discrete lines. The radiative properties and the validity of the various plasma equilibrium models within the hollow cathode have also been discussed.