Diffusion and density of atoms in strongly ionized inhomogeneous $\rm He$ plasma

The article demonstrates that the key link in the ionization and recombination kinetics of strongly ionized nonequilibrium $\rm He$ plasma at atmospheric pressure in a narrow water-cooled arc channel is the ionization–diffusion balance of atoms, which regulates the concentration of $n$ and electrons $n_e$ and maintains close to isochoric conditions with a high concentration of neutrals $n \sim n_e$, exceeding the Saha equilibrium by two or three orders of magnitude. Using the measured radial dependences $n_e(r)$ and $T(r)$, the problem of the diffusion of atoms in a binary mixture is solved approximately, taking into account the ambipolar diffusion of an electron–ion gas as one of the components of the binary mixture. The concentration of atoms at the center of the arc and its radial dependence, which strongly increases with distance from the center, is found, especially with powerful pulsed heating of a stationary arc. The pressure when the pulse is applied reaches its maximum and is twice the atmospheric pressure. Due to the high concentration of atoms and destruction of levels by plasma microfields, triple recombination is ten times weaker than ambipolar diffusion. One of the consequences of the predominant ambipolar diffusion in the kinetics of charged particles is the low density of double ions $n^{++}/n^+ \sim 10^{-3}$.