Abstract: A microwave energy plasma source comprises a cylinder with a top lid that allows a centrally located plasma tube to be supplied with a process gas. On opposite sides of the cylinder walls are located a pair of push-pull air fans that provide a cooling air flow through the inside chamber of the cylinder. Orthogonal to the pair of fans, a microwave energy applicator is mounted to the cylinder walls and has a ring type slow wave structure which surrounds the plasma tube. The bottoms of the cylinder and the plasma tube are connected through a coupler to a process chamber in which is situated a semiconductor wafer being processed. In alternative embodiments, the cylinder has included a movable planar floor and ceiling between which is formed a tunable microwave cavity. Such top and bottom tuning plates are adjusted such that the microwave source impedance is optimally matched to the microwave applicator terminating impedance by affecting the tuned frequency of the ring type slow wave structure.