Power dependencies of the surface impedance of Y-Ba-Cu-O

Abstract

Abstruct-The application of HTS is obstructed by the nonlinear behavior of Z(T,f,Hd) with rf field. The study of those nonlinearities profits by carefully calibrated rf measurements in the frequency and time domain, which yield 6Rs(H) = H" = 6Xs(H). In contrast to SRs(H) = H", the ratio r=GXs/GRs is independent of geometry factor and shows distinct T and f dependencies for various mechanisms and rf set-ups. The high power rf response in the frequency domain yields nonlinear resonance curves, n and r values. The time domain measurements give useful insight about dynamics of the underlying nonlinear mechanisms. The results r = 1 and n = 1-2 are in line with Josephson fluxons in weak links, which may interact with dc fluxons threading through the weak links.

Power handling capabilities of Y-Ba-Cu-O wafers and patterned microstrip resonators

“…The parameters of the dielectric resonator are listed in Table I. To avoid thermal effects, time domain measurements have been used at high microwave powers [6]. The optimal relative phase of the rf signal has been preliminary set and the quality factor was determined by the analysis of the decay curves after short (typically 200 psec) microwave pulses.…”

“…3 and Table 11. The time and frequency domain analysis of Z,(H,f) yielded r -1 for outer and inner surfaces and no heating [6]. The gray scale R,-map of KarL207 in Fig.…”

“…degradation of the power handling capabilities of microwave devices and harmonic generation. In spite of the intensive research, the mechanisms responsible for the nonlinear behavior of the surface impedance are not fully understood [4], [6]. Furthermore, the performance of the microwave devices may be affected by the patterning processes.…”

Microwave performance of high-density bulk MgB2

“…19,21 The initial enthusiasm regarding large-scale and inexpensive microwave applications of YBCO material that operate at liquidnitrogen temperatures has somewhat cooled over the years mainly because of the observation of unconventional superconductivity that causes slower-than-exponential drop of R s below T c /2 and the detrimental effects of weak-links present in not only polycrystalline and biaxially-textured, but also epitaxial thin films. 22 The presence of weak-links and the strong dependence of the associated Josephson current on the misalignment angle of the grains lead to flux penetration into polycrystalline and biaxially-textured samples at very low current levels. 23 This in turn leads to high and nonlinear microwave losses at very low dc and microwave magnetic field levels (<1 Oe).…”

Effects of Electric and Magnetic Fields on the Performance of a Superconducting Cavity

“…Several models have been proposed over the last few years to explain the origin of these "anomalous losses". A model by Halbritter [1], describes the Q-drop as due to an interface tunnel exchange process occurring between conduction electrons from the metals and electrons trapped in localized states in the surface oxide. This phenomenon is supposed to be driven by an intense electric field.…”