  We report the first successful extraction of accumulated ultracold neutrons
(UCN) from a converter of superfluid helium, in which they were produced by
downscattering neutrons of a cold beam from the Munich research reactor.
Windowless UCN extraction is performed in vertical direction through a
mechanical cold valve. This prototype of a versatile UCN source is comprised of
a novel cryostat designed to keep the source portable and to allow for rapid
cooldown. We measured time constants for UCN storage and extraction into a
detector at room temperature, with the converter held at various temperatures
between 0.7 and 1.3 K. The UCN production rate inferred from the count rate of
extracted UCN is close to the theoretical expectation.
