High-Q niobium klyston cavities for use in gravitational wave detectors

The main purpose of this work was to measure the resonant frequency and the Q-factor for the niobium superconducting reentrant cavities to be used in parametric transducers of the gravitational wave detector Mario Schenberg. Many cavities were manufactured from niobium with high tantalum impurities (1420 ppm) and they were cryogenically tested to determine their resonance frequencies and unloaded electrical quality factors (Q₀) related to the electromagnetic coupling. These cavities were closed using a niobium cover with tantalum impurities below 1000 ppm and the unloaded electrical quality factor Q₀ = 2.65 × 10⁵ was obtained. Another cavity similar to the one used by the Australian detector Niobe and made of niobium with low tantalum impurities was also investigated. The unloaded quality factor measured for this cavity was Q₀ = 6.35 × 10³. The experimental tests were performed in the laboratories of the National Institute for Space Research (INPE) and the Institute for Advanced Studies (IEAv-CTA).