A microwave applicator (10) including a tunable cavity (12) having by an elongated casing formed from a transition section (14) axially secured between upstream and downstream end sections (16) and by first and second end assemblies (28) each axially movable in the elongated casing. A tube assembly (72) passes through and is rotatably supported within tubes (36) of the end assemblies (28) and passes through the elongated casing. Material in the tube assembly (72) in the elongated casing and between the end assemblies (28) are subjected to microwave power introduced into the transition section (14) by a waveguide (110) via an opening 20. The axis of the tube assembly (72) is adjustably offset from that of the elongated casing and the transition section (14) is adjustably fixed at various circumferential positions to superimpose the material bed in the tube assembly (72) with the area of highest field strength. Material is introduced into the tube assembly (72) by an auger (90) having holes (92) in the spiral flight above the material to allow air to flow concurrently with the material in the auger (90) and in the tube assembly (72). The tube assembly (72) includes a tube (74) formed by sections (74A, 74B) interconnected together by generally T- shaped extensions (132, 133) which interfit in generally T-shaped slots (120, 121) formed on the axial ends of the sections (74A, 74B). A control system (170) is used to adjust operating parameters for the applicator and includes a generator (146), a network analyzer (148), a microwave switch (152), a dual directional coupler (164) and an impedance matching device (112). A method of adjusting the applicator (10) to overcouple the microwave energy to the cavity (12) includes adjusting the end assemblies (28) and an impedance matching device (112) while minimizing the reflected power.
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