  We describe a helium source cell for use in cryogenic experiments that is
hermetically sealed $in$ $situ$ on the cold plate of a cryostat. The source
cell is filled with helium gas at room temperature and subsequently sealed
using a cold weld crimping tool before the cryostat is closed and cooled down.
At low temperature the helium condenses and collects in a connected
experimental volume, as monitored via the frequency response of a planar
superconducting resonator device sensitive to small amounts of liquid helium.
This on-cryostat helium source negates the use of a filling tube between the
cryogenic volumes and room temperature, thereby preventing unwanted effects
such as such as temperature instabilities that arise from the thermomechanical
motion of helium within the system. This helium source can be used in
experiments investigating the properties of quantum fluids or to better
thermalize quantum devices.
