Liquid helium pump

In a pump for driving liquid helium, including a pump housing having means defining a pump inlet and a pump outlet;

• a pumping member arranged in the housing for reciprocating motion parallel to a pump axis for drawing liquid helium into the pump through the pump inlet and driving liquid helium out of the pump through the pump outlet;
• and an electromagnetic drive means contained in its entirety in the pump housing for generating an axially oriented force applied to the pumping member to reciprocate the same;
• the improvement wherein said electromagnetic drive means comprises:
• (a) a stationary electromagnet supported in said pump housing and including
• (1) non-magnetic first and second coil carriers fixedly supported in said pump housing and surrounding said axis;
• said second coil carrier coaxially surrounding said first coil carrier and defining therewith an annular clearance constituting an air gap surrounding said axis and having a length dimension parallel to said axis;
• (2) first, second, third and fourth superconductive energizing solenoids carrying an energizing current to generate a magnetic flux in said air gap;
• said first and second energizing solenoids being mounted in an axially spaced relationship on said first coil carrier;
• said third and fourth energizing solenoids being mounted in an axially spaced relationship on said second coil carrier;
• said first energizing solenoid being in radial alignment with said third energizing solenoid and said second energizing solenoid being in radial alignment with said fourth energizing solenoid;
• (b) a non-magnetic third coil carrier attached to said pumping member to move therewith as unit;
• said third coil carrier surrounding said axis and having a travelling path passing through said air gap and being parallel to said axis;
• (c) a superconductive cylindrical moving coil carrying a control current and being mounted on said third coil carrier coaxially with said first, second, third and fourth energizing solenoids for traversing the magnetic flux in said air gap whereby an electromagnetic force parallel to said axis is exerted on said moving coil for displacing said moving coil, said third coil carrier and said pumping member as a unit;
• said moving coil having an axial length which is at least approximately equal to the axial distance between said first and second energizing solenoids;
• and
• (d) means for supplying first, second, third and fourth energizing solenoids and said moving coil with said energizing current and said control current, respectively.