J. A. M. van der Mullen

Atmospheric microwave-induced argon plasmas with and without analyte injection have been exposed to power interruption experiments in order to study transport processes and to reveal dominant excitation balances. From the time-dependent behaviour of line intensities due to electron cooling and quenching during the power interruption, it is found that electron loss channels, such as diffusion, convection and the dissociative recombination of molecular ions, are much larger than for inductively coupled plasmas. It is found that in the ionizing part of the plasma electron dominated mechanisms are responsible for the population of radiative levels. Significant changes in the responses to power interruption are observed when small amounts of molecular compounds are injected (>0.5%), probably due to a decrease of the electron density. Furthermore, it is found that in the recombination zone downstream in the plasma an electron-independent excitation mechanism, probably thermal excitation, is responsible for the population of radiative levels of analytes with relatively low excitation energies. From the downstream propagation of a disturbance created in the ionizing part of the plasma the local axial gas velocity has been determined. In the analyte excitation zone of the plasma typical velocities are around 25 m s^-1, whereas in the recombining zone velocities of 12-18 m s^-1 are obtained.

A collisional radiative model is presented for mercury discharges with electron temperatures between 0.75-2 eV and electron densities between 10¹⁸-10²⁰ m^-3. Such plasma parameters are encountered in a number of modern light sources, such as mercury-operated induction lamps and the compact fluorescent lamp. The analytical top model has been used, which allows the majority of the non-equilibrium levels to be taken into account implicitly. As a result, indirect ionization processes involving highly excited atomic mercury states are taken into account in spite of the relatively low number of levels (19) which has been considered. The influence of higher atomic mercury levels on the ionization rate coefficient has been carefully analysed, and has been found to contribute significantly. Furthermore, a consistent means of quantifying the production of radiation by the plasma will be presented by introducing the specific effective emissivities. These enable one to express the total radiated power in terms of the densities of the transport-dominated states and the electron density and temperature. These coefficients, as well as the net coefficients of ionization and recombination, will be presented and discussed, enabling their usage in plasma transport models.

It is recognized that the preceding Comment by Bakshi adds a consistent result to our generalization. However, the usefulness of this result in experimental situations is doubted. A note is added about another point addressed in the Comment [V. Bakshi, Phys. Rev. A 42, 2460 (1990)], i.e., the correct expression for the equilibrium population of an excited state for two-temperature plasmas of which the excitation population distribution is nonlocal thermodynamic equilibrium below a certain level q>1.