  Dark Matter (DM) is one of the most critical questions to be understood and
answered in fundamental physics today. Observations with varied astronomical
and cosmological technologies already pinned down that DM exists in the
Universe, the Milky Way, and the Solar System. However, the understanding of DM
under the language of elementary physics is still in progress. DM direct
detection aims to test the interactive cross-section between galactic DM
particles and an underground detector's nucleons. Although Weakly Interactive
Massive Particles (WIMPs) is the most discussed DM candidate, the null-WIMPs
conclusion has been consistently addressed by most convincing experiments in
the field. The low-mass WIMPs region (100s MeV/c$^2$ - 10 GeV/c$^2$) has not
been fully exploited comparing to high-mass WIMPs (10 GeV/c$^2$ - 1 TeV/c$^2$)
experiments which implement liquid xenon or argon TPCs (Time Projection
Chambers). The ALETHEIA experiment aims to hunt for low-mass WIMPs with liquid
helium-filled TPCs. In this paper, we go through the physics motivation of
low-mass DM, the ALETHEIA detector's design, a series of R&D programs that
should be launched to address a liquid helium TPC's functionality, and possible
analysis channels available for DM searches. We designed and homemade a 30 g
liquid helium prototype detector at CIAE. In Summer 2021, the detector was
cooled down to 4.5 K successfully. The detector's dark current is less than ten
pA for an external voltage up to 17 kV/cm when filled with vacuum, 1 atm
nitrogen gas, and liquid nitrogen.
