An electric-motor assembly for installation in a borehole to power a
downhole tools such as a pump has a first impermeable tube defining an
axis and a stator fixed in the tube and having a series of coiled
windings and laminations and electrically insulating potting in which the
laminations and windings are imbedded. The windings have a connection to
an electronically controlled power supply. An annular rotor in the tube
radially surrounding the stator includes a permanent magnet coaxial with
the windings. The tube seals the stator and rotor from the environment.