Interaction of thermionic electrons with an argon cathode plasma

Elastic and inelastic interactions of thermionic electrons with the particles in an atmospheric pressure argon cathode plasma are analyzed. It is shown that for an equilibrium plasma the beam of thermionic electrons is attenuated primarily through elastic collisions with atoms, electrons, and ions in the plasma near the cathode. The contribution of inelastic interactions to the attenuation of the beam is small. In a weakly ionized plasma the elastic scattering of thermionic electrons on atoms predominates. At high temperatures, when $n_e \gtrsim n_a$, the thermionic electrons are primarily scattered on charged particles. It is found that in thermochemically nonequilibrium plasmas with $T_e > 14,000$ K, besides scattering on the plasma electrons, elastic scattering on atoms can make a significant contribution to the attenuation of the beam of thermionic electrons.