The determination of the radial profile of the ground state density without assuming local thermodynamic equilibrium (LTE) conditions in around atmospheric pressure (0.01 MPa<p<0.3 MPa) discharges used as light sources is a worthy investigation subject. This work deals with the high-pressure mercury discharge which could be considered as a “test case.” Particularly useful for the diagnostics of these plasmas is the self-reversed resonance mercury line 253.7 nm. In this article, two independent experimental methods were used: emission spectroscopy, called the “ΔλR method,” and interference shift measurements “hook method.” Using the Hg-253.7 nm resonance line, both experimental methods indicate similar deviations from LTE in particular for the lower pressure discharges (p<0.04 MPa). In those cases, the experimental errors for both methods are significantly lower than the detected deviations. Furthermore, the measured deviations are in good agreement with predicted values from a two-temperature, two-dimensional fluid model developed elsewhere.
The radial distributions of the temperature and particle density are of decisive importance for the understanding of high-pressure gas discharges. The present paper deals with the measurement of radial density profiles of the excited Hg states 6, 6 and 6 and the determination of the temperature profiles in conventional 250 W high-pressure Hg and discharge lamps. The population densities are determined using the interferometric hook method and the arc temperature by emission spectroscopy. From the density distribution the radial temperature profiles are deduced. They agree well with those determined by emission spectroscopy. It is demonstrated that the hook method is also applicable to such discharges sustained in cylindrical discharge tubes which are usually not very suitable for interferometric measurements.
We consider the nonlocal theory of a positive column in a glow discharge in two cases, where the mean free path of charged particles is either greater than the discharge tube radius (the free-flight regime) or much less than the radius (the collisional regime). The great bulk of electrons, which determines the density and the discharge current in the axial direction, appears to be trapped by the radial field of a positive column. The electron flux to the wall, which compensates for the ionization in a volume, is determined by fast electrons with energies of the order of wall potential, which are able to leave in a loss cone. The electron kinetic equation, which is solved by averaging it over the radial transits for the two regimes considered, permits us to obtain the electron density and the ionization rate. Thus, we develop the theory of a positive column for the non-Boltzmann electron distribution in the radial field. Under the free-flight regime, this theory is developed by analogy with the Langmuir-Tonks one. Under the collisional regime, the spatial distribution of the potential is obtained from the ion motion equation with the ambipolar diffusion coefficient, which depends on the radial coordinate. The concrete calculations are carried out for the xenon discharge under the free-flight and collisional regimes. The theoretical calculations are compared with the results of experiments on the measurements of the electric field and the densities of metastable and resonance xenon atoms.
Time resolved absolute density measurements of the lss (metastable) and ls4 (resonance) level in the positive column of a pulsed xenon gas discharge for gas pressures between 1 and 40 Torr and currents between 100 and 300 mA are presented. The densities ranged from 1 x 10" to 5 x 10l2 cm-3 and were found to be ten times larger in the afterglow than in the active part of the discharge. The enhanced radiation obtained in the afterglow in the near infrared regions as well as in the VUV region is caused by a dissociative recombination and formation of excimer states.
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