Plasma density measurements by electron-plasma wave pulses in a Q-machine

An accurate determination of plasma densities in a Q -machine can be given by observations of electron-plasma wave pulses. A universal chart to evaluate the plasma density from the propagation speed of wave pulses is provided. It is shown that the radial density distribution should be taken into account in this diagnostic method. Comparison between this method and Langmuir probe methods is presented. It is concluded that speed measurements of electron-plasma wave pulses offer a rapid reliable method for determining the density of a low-density plasma (10 6 -10 9 cm −3 ).