Electron Density Measurements in the Magnetically Confined Arc

Three methods were used to obtain electron density as a function of radius in a magnetically confined, low-pressure argon arc. The first utilized the phase shift of a reflected 35-kMc/sec microwave, and the second determined density from the ion saturation current to a Langmuir probe. The third determination utilized the broadening of the H β line emitted by a small quantity of added hydrogen. Agreement among the three methods is satisfactory; the electron density at the axis of this discharge is of order 1014 cm−3, in agreement with results obtained by others for discharges of similar type.