Superconductivity Superconducting Resonant Cavities

The imaginary part of the surface impedance, the surface resistance,also plays an important role. It results in a small perturbation of the resonant frequency of the cavity relative to that for perfectly conducting walls. It is important in superconducting resonators because in the superconducting state the surface reactance, and consequently the resonant frequency, vary slightly with temperature. The fractional perturbation of the resonant frequency is given by... 

Although the role of surface reactance is rarely considered in ordinary resonators, it cannot usually be ignored in superconducting resonators. As mentioned earlier, the surface reactance re suits in a slight correction to the resonant frequency in superconductors. In a superconductor, the surface reactance is temperature dependent and is related to the temperature dependence of the static penetration depth. The effect is small but cannot be overlooked if one is interested in using a cavity as a stable reference element. Figure 4 illustrates the temperature dependence of the resonant frequency of a tin cavity due to this cause. 

Low-magnetic-field applications. These applications include Josephson-effect devices, magnetic-flux shields, transmission fines, and resonant cavities, all of which require superconducting materials having a high critical temperature and a high critical magnetic field. 

The main difficulty arises due to the low losses of many microwave oxide materials including insulator and superconducting metals. Therefore, approaches based on a sample being just a small perturbation of the dut, such as a cavity resonator with a small piece of material inside, are of limited use, because the effect of the sample absorption on the resonator Q is too small. Therefore, in most cases the geometry of the sample has to be selected in a way that the sample itself represents a dominant part of the dut. 

Enhanced spontaneous emission of radiation from Rydberg atoms was reported in 1983 by Goy et al.t59], in this experiment excited sodium atoms (in the 23S state) were formed within a superconducting cavity resonant at 3 0 GHz. This frequency closely corresponds to the... 

The geometrical shape of the cavity and the specific mode selected will of course govern the Q and these considerations are always present in any resonator problem. In the superconducting cavity, however, the geometry and mode structure nave an important bearing on the fabrication methods that may be used. For example, suppose we wish to make a cylindrical resonator. In order that the active surface area be in a reasonably good physical state, we would probably make it in two separate halves, so that the inside surfaces could be reached for subsequent electropolishing. However the cavity has to be split in such a... 

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