Dielektrische Wellenleiter als Plasmasonden

A microwave interferometer is described, by which the electron density in a small volume inside of a plasma can be measured. By dielectric rods acting as waveguides the microwave is led to this volume. For a given electron density the phase shift is calculated for this volume and for the dielectric rods. By a suitable choice of the radius and the dielectric constant of the rods the phase shift along the rods can be surpressed. The influence of plasma sheaths is discussed. In a special application to the plasma of the negative glow these interferometric measurements are compared with Langmuir probe measurements.