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

A new and simple method for precise measurements of electron density in a plasma with use of plasma oscillations is described. A weak electron beam is injected from a hot filament and excites electron waves oscillating at the plasma frequency wp, whose sharp spectrum, obtained using a detector, gives the electron density. This plasma oscillation method is free of many difficulties often encountered with a Langmuir probe, such as thin film deposition, plasma potential fluctuation, and magnetic fields. The measurement technique is theoretically analyzed and experimentally demonstrated in the density measurements of an inductively coupled rf plasma, together with a comparison with the Langmuir probe method.