Collisional Drift Waves in the Linear Regime

A method of external excitation of density gradient drift waves in a stable, collision-dominated plasma is presented whereby the linear theory of drift waves is verified. The procedure permits limitation of the perturbation amplitude such that e∅1/kT < 0.1. This represents a new approach in the study of drift waves since nonlinear saturation effects present in all previous experiments on these waves are avoided. The driven oscillations are coherent, nearly sinusoidal modes on which measurements of ω and k as a function of the plasma parameters are made. In this manner the linear dispersion relation derived from the fluid equations is verified demonstrating the strong stabilizing effect of transverse diffusion resulting from ion viscosity. In connection with this an additional damping process resulting from ion loss at the cathodes is introduced whereby complete stabilization of the plasma to drift waves is possible. Next, the functional dependence of the phase angle between the density and potential perturbation is shown and correlation between the phase angle and the growth rate is discussed. Finally, verification of the dependence of the axial wavelength on the sheath conditions at the plasma cathode boundary and on the length of the plasma column is demonstrated.