The effect of radiative cascade on electron excitation temperature measurements

Abstract

Electron excitation temperatures have been measured in a low-pressure (0.05-Torr Cs, 2-Torr total pressure) argon-cesium discharge that uses a heated cathode (900–1100 K). The excitation temperature determinations are based upon a model that allows calculation of cesium excited state densities for low electron density (<1011 cm−3). The model assumes that the dominant creation processes for excited states are electron impact excitation from the ground state and radiative cascade from higher levels, while destruction is by spontaneous emission. Maxwellian electron energy distributions were used and the plasmas were considered to be optically thin. The model indicates that cascade contributions to the production of excited states can be as high as 50% for some cesium levels. Predicted emission spectra with cascade contributions to spontaneous emission intensities agree well with measured spectra except for radiation trapped transitions from low nP states to the ground state. Excitation temperatures are determined by fitting measured and calculated spectra.

Increased 14C AMS Efficiency from Reduced Competitive Ionization

“…The Cs(7s,p) states in near resonance with the EA of carbon are created by both electron excitation from Cs(5d) and by radiative relaxation from higher states. Marcum et al (1991) find that 30% of the Cs(7p) population in an electron excitation cell arises from radiation cascade from higher states. The RET mechanism for carbon on cesium is outlined in Figure 2.…”

Spatially resolved atomic excitation temperatures in CH4/H2and C3H8/H2RF discharges by optical emission spectroscopy

“…Quenching of metastable and excited states by heavy particles is also unimportant for excitation in the pressure range of this experiment (Kass and Williams 1973). In addition, de-excitation by collisions with ground state molecules is unimportant and can be negligible for collisions with electrons (Marcum et al 1991). Furthermore, the stepwise excitation and ionization of metastable states of the argon atoms should be very low in comparison with the concentration of the groundstate argon atoms.…”