Fig. 4: Extension of spatial afterglow model to atmospheric pressure.

a Dimensionless charge density, η, as a function of axial distance at the following constant parameters: T_e = 1.5 eV, Q = 1000 sccm, and Λ = 1.91 mm. In addition to atmospheric pressure, calculations at 75 and 300 Torr are shown for comparison. b Dimensionless charge density, η, as a function of axial distance at different gas flow rates, Q, of 500, 1000, and 2500 sccm and the following constant parameters: n_p = 4.1 × 10²⁰m⁻³, T_e = 1.5 eV, Q = 1000 sccm, and Λ = 1.91 mm. c Dimensionless charge density, η, as a function of axial distance at a tube inner diameter (characteristic diffusion length), Λ, of 1.18, 3.85, and 7.00 mm and the following constant parameters: n_p = 4.1 × 10²⁰m⁻³, T_e = 1.5 eV, Q = 1000 sccm, and Λ = 1.91 mm. In all cases, background gas temperatures were assumed to be uniform and equal to one of two limiting conditions: an upper bound temperature at the plasma- afterglow boundary calculated using a heat transfer model, or a lower bound temperature of room temperature.