  A dual-phase TPC (Time Projection Chamber) is more advanced in characterizing
an event than a single-phase one because it can, in principle, reconstruct the
3D (X-Y-Z) image of the event, while a single-phase detector can only show a 2D
(X-Y) picture. As a result, more enriched physics is expected for a dual-phase
detector than a single-phase one. However, to build such a detector, DC HV
(High Voltage) must be delivered into the chamber (to have a static electric
field), which is a challenging task, especially for an LHe detector due to the
extremely low temperature, $\sim$ 4 K, and the very high voltage, $\sim$ MV
(Million Volts). This article introduces a convincing design for transmitting
$\sim$ MV DC into a 4 K LHe detector. We also report the progress of
manufacturing a 100 kV DC feedthrough capable of working at 4 K. Surprisingly,
we realized that the technology we developed here might be a valuable reference
to the scientists and engineers aiming to build residential bases on the Moon
or Mars.
