A method is presented to determine the electron temperature in a low pressure argon plasma using emission spectroscopic measurements and a collisional radiative (CR) model. Absolute line intensity measurements are made in order to construct the atomic state distribution function. In addition to the excited states, the ground state density is also taken into account. Because of this, the excitation temperature can be determined with high precision. A CR-model has been used to determine the degree of equilibrium departure and to obtain the relationship between the excitation temperature and the electron temperature. This method is applied to a microwave plasma which has been generated inside a quartz tube using a surfatron device. The densities of argon levels close to the continuum are used to get an estimated value of the electron density. These values are used as input data for the CR-model. For an argon pressure of 6 mbar, the 4p level densities vary between 8 × 1014 and 6 × 1015 m−3. Using the estimated values for the electron density, between 2 × 1019 and 3 × 1019 m−3, the electron temperature was found to range between 1.15 and 1.20 eV. An extensive error analysis showed that the relative error in the electron temperature is less than 6%.
Convection and diffusion in the discharge region of a metal halide lamp is studied using a computer model built with the plasma modelling package Plasimo. A model lamp containing mercury and sodium iodide is studied. The effects of the total lamp pressure on the degree of segregation of the light emitting species are examined and compared to a simpler model with a fixed temperature profile. Significant differences are observed, justifying the use of the more complete approach.
By using a 3 electron-group model to describe the deviation
from a Maxwellian electron energy distribution, a collisional
radiative model describing a low temperature Ar-Hg plasma is
greatly improved. Previously, the ionisation mechanisms of such
plasmas, commonly used in fluorescent lamps, could not be
satisfactory modelled. Where using a Maxwellian electron energy
distribution showed the production of argon ions to be dominating
over the production of mercury ions, the 3 temperature approximation
yields a mercury ionization rate which is 30 times larger than the
argon ionization rate.
When a plasma is sustained in the open air, nitrogen will diffuse into the plasma. Especially for plasmas sustained by the 'Torche à Injection Axiale' (TIA) this appears to be the case, since this turbulent jet draws gases from the surroundings. In the argon plasma the entrained nitrogen is probably converted into N + 2 (via charge transfer with argon ions), which is consequently destroyed by dissociative recombination (DR). This mechanism affects the plasma in two ways: (1) it offers an important loss channel for the free electrons and (2) the gas is heated by the kinetic energy of the nitrogen atoms produced in the DR reaction.
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