ABSTRACT
A 1-D, steady state model for a low-pressure Ar-Hg plasma has been recently developed and used to study a positive column discharge with properties similar to the conventional mercury fluorescent lamp [1]. The model consists of the nonlocal electron Boltzmann equation for the Electron Energy Distribution Function (EEDF) coupled to a collisional-radiative equilibrium model for 5 Ar and 11 Hg species, the gas thermal balance equation, and an equation for the ambipolar potential. The axial electric field is calculated selfconsistently. Effects such as radial cathaphoresis are also accounted for. The inclusion of the spatial gradient term in the electron Boltzmann equation enabled the accurate treatment of the electron particle and energy transport, as well as the radial space-charge confinement. The kinetic model is self-consistently coupled to a 1-D radiation transport model through species population dynamics. The latter includes the isotope structure of the 254 and 185 nm lines, the effects of foreign gas collisional broadening, partial frequency redistribution of the emission profile for the 185 run line, Voigt profiles for all other lines, and nonlocal photopumping. This is the first model, which incorporates spatial variation in the electron Boltzmann equation and a non-local radiation transport. The radially dependent EEDF, escape factors and coupling coefficients, electron density and mean energy, electron impact excitation and ionization rates, electron particle and power balance terms and energy fluxes, UV and visible radiation, are investigated and compared with radially resolved fluorescent lamp data. The chosen discharge conditions are characteristic of mercury fluorescent lamps: p1157.5 mTon-, pAr=3 Ton, 1=400 mA, and rw 1.8 cm. The numerical solution of the electron Boltzmann equation yields the isotropic distribution versus total energy a. After transformation of the EEDF from total energy a to kinetic energy u one can compare the local EEDFs. This is shown in Fig.l, where the normalized EEDF f,(r,u) at various normalized positions r/r, is plotted. From the figure it is immediately obvious that the EEDF cannot be considered as local, particularly close to the bulb wall. The EEDF agrees well with experimental data [2] for kinetic energies of up to 10 eV.
