LAUSR

Electrodynamic characteristics of a low-pressure (electron collision frequency much lower than the field frequency) capacitive HF discharge maintained by an electromagnetic field with a frequency between 13 and 900 MHz are studied analytically and numerically. It is demonstrated that the field of both the fundamental mode (the field in the metal–space-charge sheath–plasma–space-charge sheath–metal structure) and the field of the higher-order evanescent modes must be taken into account for correct calculation of discharge characteristics under such conditions in a wide range of electron densities. Expressions governing the amplitudes of excited waves, along with expressions governing the discharge impedance in the presence of these waves, are derived by using field expansion in eigenwaves of an empty waveguide and eigenmodes of the three-layer structure. The case in which the size of plasma is smaller than the size of the electrodes is analyzed in detail. In this case, excitation of higher-order types of waves in the plasma column is generated by axial plasma inhomogeneity and is not related to electrodynamic effects near the electrode boundaries. It is demonstrated that the positions of current and voltage resonances related to propagation of surface waves along the three-layer structure becomes substantially modified due to excitation of higher-order field modes of the same structure. In addition, resonances caused by excitation of standing surface waves near the lateral surface (resonances of higher-order modes of the three-layer structure and an empty waveguide) can take place. Variation of relative position of resonances caused by changes in the discharge chamber geometry is investigated. Obtained results qualitatively agree with the results of numerical calculation of the discharge impedance and field propagation in the discharge by COMSOL Multiphysics® software package.