Effects of fluxoid trapping on signal creation in superconducting tunnel junction X-ray detectors

Trapping of fluxoid quanta influences the performance of tunnel junction X-ray detectors. It has been found that the trapped vortices corresponding to a terrestrial magnetic field are enough for charge output and quasiparticle losstime to decrease by factors of two and three, respectively. This result leads to an effective vortex radius of Reff=3ξ, which is in a good agreement with a Golubovʹs calculation. Magnetic images by a scanning SQUID microscope show that the trapping takes place at junction edges or inside the junction at random. The random trapping may cause an instability of the detector performance. On average, the cooling in a perpendicular magnetic field results in the trapping of the corresponding vortex density, that is B/Φ0.