Probing plasmas with ion acoustic waves

Since Langmuir's pioneering studies, low temperature plasma studies have evolved from single positive ion species plasmas, to plasmas with combinations of positive and negative ions in addition to electrons, to plasmas with very heavy negative dust ions. The use of ion acoustic waves, first recognized by Langmuir, as a diagnostic of plasma parameters based on wave frequency, wavelength and phase velocity data in a wide variety of low temperature plasmas, is reviewed. Dispersion relations for all types of unmagnetized plasma are derived as special cases of a single general dispersion relation. Complications associated with grid excitation, such as wave diffraction, excitation of waves at other plasma boundaries and particle burst pseudowaves, are also discussed. © 2009 IOP Publishing Ltd