Experimental Verification of Landau Waves in an Isotropic Electron Plasma

摘要

We report here measurements of dispersion and damping of plane electrostatic waves having phase velocities between 1.5 and 3 times electron thermal speed 3×107 cm/sec. These waves were excited and detected at frequencies ωp≪ω≪2.5ωp using gridded rf probes within an isotropic, quiescent, and collision‐free sodium plasma at thermal equilibrium. As plasma electron density (1×107 to 2×108 cm-3) and rf (30 to 180 MHz) are varied, the measured wavelengths and spatial damping rates were scaled to Debye length using independent Langmuir probe data. Full agreement is then found between the experimental results and the fundamental solution of Landau''s dispersion relation.