A probe investigation of the structure of electrode microwave discharge in nitrogen

A probe investigation is performed of the structure of electrode microwave discharge in nitrogen at a pressure from $0.5$ to $2.5$ torr, incident power of up to $500$ W, a power of $10$ to $50$ W absorbed in the system, and a gas flow rate from zero to $1000$ cm$^3$/min under normal conditions. It is demonstrated that, if the discharge diameter exceeds considerably that of antenna, the discharge is a close-to-spherical formation with a clearly defined boundary. The antenna is surrounded by a bright luminous film of plasma. A considerable nonuniformity of the parameters of the electron component of plasma and of constant potentials in plasma is demonstrated. It is possible that the discharge structure is related to the existence of a region of self-maintained discharge (luminous film surrounding the electrode) and a region of semi-self-maintained discharge (spherical region). The existence of considerable constant fields in the plasma of an electrode microwave discharge is found, whose emergence may be due to a nonlinear transformation of the microwave power maintaining the discharge. The discharge is surrounded by an isotropic region with decreasing electron temperature and concentration.