High-Q superconducting niobium cavities for gravitational wave detectors

The main purpose of this work is to optimize the electric Q-factor of superconducting niobium klystron cavities to be used in parametric transducers of the Mario Schenberg gravitational wave detector. Many cavities were manufactured from niobium with relatively high tantalum impurities (1420 ppm) and they were cryogenically tested to determine their resonance frequencies, unloaded electrical quality factors (Q0) and electromagnetic couplings. These cavities were closed with a flat niobium plate with tantalum impurities below 1000 ppm and an unloaded electrical quality factors of the order of 105 have been obtained. AC conductivity of the order of 1012 S/m has been found for niobium cavities when matching experimental results with computational simulations. These values for the Q-factor would allow the detector to reach the quantum limit of sensitivity of ~ 10−22 Hz−1/2 in the near future, making it possible to search for gravitational waves around 3.2 kHz. The experimental tests were performed at the laboratories of the National Institute for Space Research (INPE) and at the Institute for Advanced Studies (IEAv - CTA).