Chapter V the breakdown of dielectrics

Persson (1) derives the limitations of the conventional microwave cavity method of measuring electron density. Microscopic electric polarization can be eliminated and overlapping modes suppressed by designing the cavity so that the probing microwave field and the plasma have rotational symmetry around the same axis, thereby extending the range of electron density measurement. Following this theoretical development, Buchsbaum and Brown (2) present a method whereby much higher electron densities can be measured. The method, based on eliminating the effect of a-c space charge on the probing microwave field, is accomplished by ensuring that the electric field is everywhere perpendicular to the electron density gradients.