Magnetostrictive valves for cryogenic applications would be actuated by superconducting flux tubes (SFTs), according to a proposal. The reasoning behind this proposal closely tracks that of the proposal to use SFTs in magnetostrictive heat switches, as reported in the preceding article.
Previous versions of magnetostrictive valves for cryogenic applications were described in "Magnetostrictive Valve for Use at Low Temperature" (NPO-19480), NASA Tech Briefs, Vol. 21, No. 2 (February 1997), page 14b and "Improved Magnetostrictive Valve for Use at Low Temperature" (NPO-20271), NASA Tech Briefs, Vol. 23, No. 8 (August 1999), page 48. As in magnetostrictive heat switches, the actuators in magnetostrictive valves are magnetostrictive rods, and actuation is effected by turning magnetic fields on or off.
Magnetostrictive valves are useful primarily in cryogenic instrumentation. They are especially useful for controlling flows of liquid helium. Typically, a magnetostrictive valve is required to operate in a normally closed (energize-for-flow) mode. The magnetic fields needed for actuation of magnetostrictive valves like those reported previously can be generated by either normally conductive or superconductive solenoidal coils. It is necessary to supply current continuously to the solenoids to maintain the magnetic fields needed to keep the valves open.
SFTs for magnetostrictive valves could be made of bismuth strontium calcium copper oxide (BSCCO), as described in more detail in the preceding article. As in the case of a magnetostrictive heat switch, the main advantage of using an SFT (instead of a solenoid) to actuate a magnetostrictive valve is that the valve would remain in either the "open" or "closed" state until toggled into the opposite state by applying a pulsed current to a coil around the SFT to change the magnetic flux and thereby change the degree of magnetostriction. It may even be possible to select flux levels corresponding to states intermediate between "open" and "closed" to regulate flow; in that case, the valve would remain in the selected flow state, without power applied, until actuated into the next state.
The advantages of magnetostrictive valves actuated by either superconducting solenoids or SFTs are almost identical to those of similarly actuated magnetostrictive heat switches; low heat leakage, little or no thermal hysteresis, and functionality at the temperatures of the flows to be controlled. Valves actuated hydraulically with helium as the hydraulic fluid offer flow control with minimal thermal perturbation of cryogenic environments, but operate with response times about 100 times those of magnetostrictive valves.
This work was done by Robert Chave of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Physical Sciences category.