Comparative Measurements Between Langmuir Probe And Ion-Acoustic Wave Detection In A Radio Frequency Source

Phase velocity or damping measurement of ion-acoustic waves in plasmas is an alternative diagnostic technique to measure the electron temperature T-e in presence of radio frequency (RF) fluctuation. If a fraction of the ion population in plasma is made of negative ions, the dispersion relation of this wave has characteristic features. The ion-acoustic wave has two modes of propagation in negative ion enriched plasmas. The phase velocity of fast mode increases and damping decreases with increasing negative ion concentration. The slow mode is highly damped. Measurements in the range of 1kHz-40kHz in H-2+Cs and Xe+Cs plasmas, where negative ion concentration is much less compare to other electronegative plasmas, like SF6-, O- etc., show that the wave propagates according to the slow wave dispersion relation. The ion-acoustic derived T-e measurements are presented in two different geometries and compared with the T, value derived from the Langmuir probe characteristic. (C) 2004 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim.