DETECTION OF ION-PLASMA WAVES BY COLLECTIVE THOMSON SCATTERING

The first unambiguous experimental detection of ion plasma waves is reported. These short-wavelength (kDe>1), purely electrostatic ion waves were first predicted by Tonks and Langmuir in 1929. The waves are observed in a long-scalelength (L>104/k), multiply ionized (Z=22), laser-produced plasma. The frequency (), wave number (k), and amplitude evolution of the ion waves are measured by time-resolved spectroscopy of the scattering from the ion waves of a probe laser beam. The wave frequency is approximately the ion plasma frequency (pi) when kDe exceeds 1, as predicted by the theoretical dispersion relation. © 1995 The American Physical Society.