New surface wave launchers for sustaining plasma columns at submicrowave frequencies (1–300 MHz)

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Abstract
We describe new surface wave launchers intended to sustain plasma columns with high-frequency (hf) power in the range of 1–300 MHz. This frequency range complements that of the existing surface wave plasma generators (surfatron and surfaguide launchers), which are best suited to operate in the microwave domain (≳300 MHz). With the addition of this new type of launchers, called Ro-box, it is now feasible to achieve a surface wave produced plasma column at applied frequencies ranging from 1 MHz to 10 GHz. The possibility of using the same physical hf coupling mechanism (surface wave propagation) over such a broad frequency band is an unprecedented situation with hf produced plasmas. This is of interest for both fundamental and applied physics, as it allows frequency effect investigations and frequency optimization of plasma processes. The new devices can be made so that the wave-launching and the impedance-matching functions are physically separated, leading to a modular design, a feature that facilitates changing the plasma tube diameter and the operating frequency range. A further advantage of the new devices is that their launching section can be implemented around the discharge tube more compactly than with the other surface wave launchers.