Large-scaled line plasma production by evanescent microwave

Long line-shaped microwave plasma has been generated, in helium and argon gas pressure, over a pressure range of 1–50 torr. To this end, waves of 2.45 GHz are fed into a narrow flat rectangular waveguide, through a tapered waveguide. The power of microwave is coupled to the discharge gas through a linear-slot antenna. The discharge is realized in a rectangular Pyrex tube, placed-in along the slot groove position. In this configuration the microwave is cut off, but the evanescent wave with a long wavelength is propagated and employed to produce the plasma. Measurements of the field distribution in the waveguide revealed that the wavelength of the excited field increases as waveguide width decreased to a width close to the cut-off width of 61.3 mm. The relative intensities of He I lines show very high uniformity along the whole line plasma length, and helium excitation temperatures were in the range of 3000–5000 K.