Volume 89, Issue 6, 15 March 2001
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
89(2001); http://dx.doi.org/10.1063/1.1345860View Description Hide Description
The vaporization of condensed materials in contact with high-current discharge plasmas is considered. A kinetic numerical method named direct simulation Monte Carlo (DSMC) and analytical kinetic approaches based on the bimodal distribution function approximation are employed. The solution of the kinetic layer problem depends upon the velocity at the outer boundary of the kinetic layer which varies from very small, corresponding to the high-density plasma near the evaporated surface, up to the sound speed, corresponding to evaporation into vacuum. The heavy particles density and temperature at the kinetic and hydrodynamic layer interface were obtained by the analytical method while DSMC calculation makes it possible to obtain the evolution of the particle distribution function within the kinetic layer and the layer thickness.
89(2001); http://dx.doi.org/10.1063/1.1346656View Description Hide Description
Using recent experimental data on the time-averaged, spatially varying plasma properties within a Hall discharge plasma, we present in this article, a theoretical study of the response of this plasma to small (linear) perturbations in its properties. As a starting point for this analysis, we assume a two-dimensional fluid description that includes a simplified equation for the electron energy, and constrain the azimuthal wave vector such that we excite only the dominant azimuthal modes. The growth rate and frequencies of predominantly axial and azimuthally propagating plasma disturbances are obtained by numerical solution of the resulting eigenvalue problem under a quasiuniform plasma condition, along the entire discharge channel. The results identify the persistence of a low frequency instability that is associated with the ionization process, concentrated largely in the vicinity of the exit plane, where the magnetic field is at its maximum value, consistent with experimental observations for the relatively low operating voltages (∼100 V) considered in this study.
Experimental study of energy coupling and plasma breakdown in a pulsed high frequency resonant cavity89(2001); http://dx.doi.org/10.1063/1.1351540View Description Hide Description
An experimental study of the electromagnetic behavior of a pulsed high frequency resonant cavity, operating in its fundamental mode, is presented. Typical pulse characteristics are a pulse width of 10 μs, microwave frequency of 1 GHz, and microwave power of a few kW. The various parameters (characteristic time τ, coupling factor β, incident power that determine the temporal variation of the electrical characteristics (power entering in the cavity,electric field) during the pulse are defined. In particular, the influence of the coupling factor on the transition stage to a steady state is discussed for the cavity without plasma. The temporal behavior of the cavity in the presence of a gas (argon and hydrogen) is also studied. For pressures ranging from 0.5 to 100 Torr, the discharge breakdown parameters (time electric field in hydrogen are deduced from the experiments μs, V/cm). The conditions to reach a quasisteady state plasma are derived from the qualitative analysis of the cavity behavior.
In situ determination of absolute number densities of nitrogen molecule triplet states in an rf-plasma sheath89(2001); http://dx.doi.org/10.1063/1.1351003View Description Hide Description
A laser induced fluorescence technique (LIF) in combination with optical emission spectroscopy(OES) and Rayleigh scattering (RS) was applied to investigate absolute number densities of the population of the three nitrogen triplet states and the metastable in an asymmetric low pressure rf discharge. Primary targets of this investigation were the three lowest vibrational levels of each triplet state and additionally of which can be populated very efficiently in the plasma sheath.Calibration of LIF intensities to absolute densities of and has been realized by comparison with the signal of the RS experiment done in pure nitrogen gas. Calibration of which we could not detect by LIF but rather only by OES was achieved after comparing OES and LIF signals of the state. Excitation energies of the analyzed states range from 6 up to 11.5 eV and the measurednumber densities differ by about seven orders of magnitude from as much as down to almost In addition to the interpretation of the results this article describes the used calibration methods which are partly based on a suggestion made by P. Bogen (Proceedings of the XVI International Conference on Phenomena in Ionized Gases, Invited Papers, edited by W. Bötticher, H. Wenk, and E. Schultz-Gulde, Düsseldorf, 1983, pp. 164–173).