A surface wave experiment on inhomogeneous plasma

The phase and attenuation characteristics of an axially symmetric surface wave on an inhomogeneous plasma column in mercury vapour have been determined using an interferometer set-up. With signal frequencies between 100 and 300 MHZ, mercury vapour pressures between 0⋅5 and 1⋅2 mtorr the attenuation coefficient varies between 0⋅75 and 5˙4 N/m. The data are compared to a cold plasma theory which takes into account the effect of profile and the loss in the glass surrounding the plasma. The resulting effective electron-atom collision frequency varies between 3×l07 and 1⋅2nbsp;× 108 sec−1. As the variation with vapour pressure and discharge current is not of the type expected by cold plasma theory, the conclusion is drawn that damping mechanisms other than collisions are present.