  We report the successful operation of a functional pixel detector with
gaseous helium cooling. Using an accurate mock-up beforehand, the cooling was
validated. We use a miniature turbo compressor to propel the helium at $2\,g/s$
under ambient pressure conditions with gas temperatures above $0^{\circ}C$. Our
earlier results based on computational fluid dynamics simulations and a much
simpler mock-up are confirmed. With this, we paved the path to cool pixel
detectors in experimental particle physics at heat densities up to $400\,
mW/cm^2$ using helium. This enables cooling of detectors with very low mass
requirements, minimising the effects of multiple Coulomb scattering
effectively. The concept presented here is not limited to pixel detector
applications and can be used to cool any surface with comparable
heat-densities, only limited by shaping the helium gas flow.
