PLASMA OSCILLATION METHOD FOR MEASUREMENTS OF ABSOLUTE ELECTRON-DENSITY IN PLASMA

A new and simple method for precise measurements of electron density i n a plasma with use of plasma oscillations is described. A weak electr on beam is injected from a hot filament and excites electron waves osc illating at the plasma frequency wp, whose sharp spectrum, obtained us ing a detector, gives the electron density. This plasma oscillation me thod is free of many difficulties often encountered with a Langmuir pr obe, such as thin film deposition, plasma potential fluctuation, and m agnetic fields. The measurement technique is theoretically analyzed an d experimentally demonstrated in the density measurements of an induct ively coupled rf plasma, together with a comparison with the Langmuir probe method.