Extension of the resonator method of determining plasma density and its application to large concentrations and volumes. I - Possibilities of a system of distributed coupling. II - Spreading of the natural frequency spectrum of microwave resonators by absorbing rings

The use of an open barrel-shaped resonator operating at a wavelength of 8-mm for determining plasma density is described. The resonator which uses a system of distributed excitation permits the measurement of density distribution up to values of 1 x 10 to the 13th/cu cm and mean density up to values of 1 x 10 to the 14th/cu cm. The upper limits of density measurement are determined by the condition of equality between the mean distance between resonance lines and the maximal frequency shift. If there is no coupling between the working mode and adjacent oscillations, then these limits can be increased several times. The second part of the paper describes the spreading of the natural frequency spectrum of the resonator by means of absorbing rings. An experimental spreading of about 5 times is obtained for a resonator of an approximate diameter of 70 mm. The feasibility of extending the method to bigger resonators for the purpose of measuring the density distribution of Tokamak plasmas is examined.