RADIAL MODEL FOR THE OPTOGALVANIC EFFECT IN THE NEON POSITIVE-COLUMN

The rate equations describing the optogalvanic effect involve the densities of the interacting particles and generally these vary spatially. This is especially true in positive column plasmas where the electron density has an approximate zero-order Bessel function profile and the metastable and resonance atom profiles may be considerably narrower, resulting in radially dependent laser absorption and excited-atom loss rates. We have included the radial dependencies in the optogalvanic rate-equation model and a final theoretical expression for the optogalvanic current perturbation has been obtained by integration over the total discharge cross-section. The results of our radial model are compared with those of the average model (where the electron and excited-atom densities are averaged over the discharge cross-section) by comparison of the 1s coupling coefficients required to fit the two theories with experimental signals obtained for the 609.6nm sign-change 1s4 - 2p4 transition of neon.