An efficient plasma beam applicator has been developed that utilizes countercurrent cooling techniques to operate at atmospheric pressure and at microwave powers in excess of 5 kW. The device has been operated continuously for tens of hours and shows no signs of degradation. Argon is used as the discharge gas and once initiated, the plasma is self-sustaining. The beam or jet of plasma is highly collimated with a beam diameter of 3 mm, is in excess of 250 mm in length, and has high heat capacity. It could potentially be used to melt industrial ceramics such as silica and alumina, but the immediate intended use is for sheet steel welding applications.