Subnormal glow discharge in a Xe/Cl2 mixture in a narrow discharge tube

Electrical and optical characteristics of a subnormal glow discharge in a short (L=10 cm) discharge tube with an inner diameter of 5 mm are investigated. The dependences of the discharge current-voltage characteristic, the energy deposition in the discharge, the plasma spectral characteristics in the 130-to 350-nm wavelength range, the emission intensities of the XeCl(D-X) 236-nm and XeCl(B-X) 308-nm bands, and the total emission intensity in the range 180–340 nm on the pressure and composition of the Xe/Cl₂ mixture are studied. Two modes of glow discharge are shown to exist: the low-current mode at a discharge current of I _ch ≤2 mA and the high-current mode at I _ch >2 mA. The transition from one mode to another occurs in a stepwise manner. The increase in the chlorine content causes the discharge voltage and the energy deposition in the plasma to increase. At low pressures of the Xe/Cl₂ mixture (P≤0.7 kPa), stationary strata form in the cathode region. The lower the discharge current, the greater the volume occupied by the strata. This longitudinal discharge acts as a powerful source of continuous broadband emission in the range 180–340 nm, which forms due to overlapping the XeCl(D, B-X) and Cl ₂ ^* bands with edges at λ=236, 308, and 258 nm. The intensity of the 236-nm band is at most 20% of the total intensity of UV radiation. The maximum power of UV radiation (3 W at an efficiency of 8%) is attained at a xenon partial pressure of 250–320 Pa and a total pressure of the mixture of 2 kPa.