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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 wind

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.

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I claim: 1. An electric-motor assembly for installation in a borehole to power a downhole tool, the assembly comprising a first impermeable tube defining an axis; a stator fixed in the tube and having a series of coiled windings and laminations and electrically insulating potting in which the lamin

I claim: 1. An electric-motor assembly for installation in a borehole to power a downhole tool, the assembly comprising a first impermeable tube defining an axis; 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 having a connection to an electronically controlled power supply, the stator forming a flowpath that extends through the stator; and an annular rotor in the tube radially surrounding the stator and including a permanent magnet coaxial with the windings, the tube sealing the stator and rotor from the environment. 2. The electric-motor assembly defined in claim 1 wherein the potting material is impervious to wellbore fluids. 3. The electric-motor assembly defined in claim 1 wherein the potting material is introduced under a vacuum. 4. The electric-motor assembly comprising a second such assembly as defined in claim 1 with the two assemblies connected in series. 5. The electric-motor assembly defined in claim 4 wherein the electric-motor assemblies are secured together and both imbedded in the potting material. 6. An electric-motor assembly for installation in a borehole to power a downhole tool the assembly comprising: a first impermeable tube defining an axis; 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 having a connection to an electronically controlled power supply; an annular rotor in the tube radially surrounding the stator and including a permanent magnet coaxial with the windings, the tube sealing the stator and rotor from the environment; a second tube coaxial with the first tube; and annular end members that substantially seal an annular space between the first and second tubes. 7. The electric-motor assembly defined in claim 6 wherein the annular end members are attached to the first and second tubes by swaging. 8. An electric-motor assembly for installation in a borehole to power a downhole tool, the assembly comprising: a first impermeable tube defining an axis; 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 having a connection to an electronically controlled power supply; an annular rotor in the tube radially surrounding the stator and including a permanent magnet coaxial with the windings, the tube sealing the stator and rotor from the environment; a metal tube set the potting; an O-ring in the metal tube; and wiring exiting from the potted material through the O-ring and metal tube.