Optical Emission from a Low-Density Argon Plasma

In many laboratory experiments, the plasma parameters do not satisfy the requirements of the various theoretical radiation models that are needed for spectral plasma diagnostics. We report here a coaxial system from which we determine the empirical relationship between the electron number density of a low-pressure argon plasma and the intensity of atomic line emission. This system is unique in that it allows the concurrent determination of electron number density and line emission intensity at various locations in the plasma. Dependence of emission intensity on the neutral background pressure and the strength of the microwave pulse, which generates the plasma, suggests that the steady-state corona model is relevant for this system.