Coupling of Helicon Antennas to Plasma Near the Electron Cyclotron Resonance
Two inductive antennas, which are usually used for the excitation of a helicon discharge on the wave azimuthal modes m = 1 and m = 0, demonstrate unexpectedly different properties near the electron-cyclotron frequency wce. Though the alternating inductive electric field E produced by the antenna m = 1 is mainly parallel to the external steady magnetic field B0, nevertheless the absorption resonance at the frequency wce accompanied by an increase in the plasma density, takes place. For the m = 0 antenna, where these fields are mutually transverse and where the cyclotron resonance seems certainly must be present, it is absent. But the electron-cyclotron resonance (ECR) appears again provided the B0 field is turned up by the right angle around the same m = 0 antenna.
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