  Quasiparticle (qp) poisoning is a major issue that impairs the operation of
various superconducting devices. Even though these devices are often operated
at temperatures well below the critical point where the number density of
excitations is expected to be exponentially suppressed, their bare operation
and stray microwave radiation excite the non-equilibrium qps. Here we use
voltage-biased superconducting junctions to demonstrate and quantify qp
extraction in the turnstile operation of a superconductor-insulator-normal
metal-insulator-superconductor single-electron transistor. In this operation
regime excitations are injected into the superconducting leads at a rate
proportional to the driving frequency. We reach a reduction of density by an
order of magnitude even for the highest injection rate of $2.4\times 10^8$ qps
per second when extraction is turned on.
