SPATIALLY-RESOLVED EXPERIMENTAL INVESTIGATION OF A SURFACE-WAVE SUSTAINED DISCHARGE IN NITROGEN

A spatially resolved experimental investigation of the electron energy distribution function (EEDF) and wave propagation characteristics in a high frequency surface wave (SW) discharge in nitrogen has been perf ormed. The measurements reveal the specific changes of the EEDF and it s integrals which occur as a result of a different coupling between th e electrons and the inhomogeneous SW electric field as a function of g as pressure. At a pressure of 0.5 Torr it was found that the EEDF and corresponding integrals depend on the spatial position, which means th at local plasma response occurs. As a result, a strong radial inhomoge neity of the discharge is observed which relates to the radial variati on of the wave field intensity. On the contrary, at 0.05 Torr nonlocal plasma response is observed. In a molecular plasma, electron energy r elaxation occurs faster than in inert gases, this being why the transi tion from the local to the nonlocal regime takes place here at a lower gas pressure. A turning back of the axial wave number due to the simu ltaneous effects of collisions and the radial inhomogeneity is also ob served. A notable feature of the experiments is that the minimum elect ron density for the wave to propagate may be smaller than the minimum density for propagation in the collisionless approximation. A strong c orrelation between the behavior of the plasma parameters and the wave electrodynamics is pointed out. (C) 1998 American Institute of Physics .