Approaches for a hard-disk drive (HDD) comprised within a sealed enclosure that is filled with a substantially helium gas are provided. The HDD may include a shroud that surrounds a majority of a perimeter of a magnetic-recording disk. The HDD may also include an upstream spoiler having one or more wings. The shape of the upstream spoiler diverts a flow of the substantially helium gas that circulates when the magnetic-recording disk is rotating from a magnetic-recording head to a plenum chamber. The plenum chamber has a mouth that allows a portion of the circulating flow of substantially helium gas to flow therein. The mouth of the plenum chamber is a gap in the shroud that is prior to the upstream spoiler in the circulating flow of the substantially helium gas. A portion of the plenum chamber is formed using a particle filter opposing the gap.