Die Theorie der Freifallsäule unter Berücksichtigung der „Neutralgasaufzehrung”︁ durch die Ionisationsvorgänge und ihre Anwendung auf Edelgas‐Ionen‐Laser

Abstract

AbstractA theory for low pressure discharges taking into account the finite mean free path of the neutral atoms for ionization is developed. The spatial distributions of the electric potential, the charged particle density, the neutral gas density, the charged particle generation, and for the ion gas the transverse particle flux, the drift velocity, the energy density and the transverse energy flux are calculated using a simplified model of the steady‐state axially homogeneous free‐falltype discharges. It is shown that increasing electric power input decreases the neutral gas density in the column. Moreover, the electron temperature depends not only on the filling pressure and the column radius, but also on the electric power input and the wall temperature. A theoretical description of the processes causing the limitations of the electron temperature, the ion wall flux, the discharge current and the degree of ionization as well as the saturation of the output power of cw noble gas ion lasers, and the slightly falling current‐voltage‐characteristic for high discharge current is derived from basic equations and the boundary conditions of the discharge.Some of the results are:The upper limit of the ion wall flux is determined by the filling pressure, the wall temperature and the atomic mass of the filling gas. The upper limit of the electric power input into the column depends on the maximum ion wall flux and the maximum electron temperature. The maximum degree of ionization is proportional to the square root of the quotient of the wall temperature and the electron temperature. The laser power output passes through a maximum with increasing electron temperature. For high densities of the discharge current the electron temperature increases slightly while the axial electric field intensity decreases weakly with rising discharge current. Furthermore, the influence of an axial magnetic field on the electron temperature, and the electron density is investigated shortly.