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.
NPO-20503
This Brief includes a Technical Support Package (TSP).
Magnetostrictive Valves Actuated by Flux Tubes
(reference NPO-20503) is currently available for download from the TSP library.
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Overview
The document discusses the development and advantages of magnetostrictive valves actuated by superconducting flux tubes (SFTs) for cryogenic applications, particularly in controlling the flow of liquid helium. Traditionally, magnetostrictive valves operate using solenoidal coils that require continuous power to maintain their state. However, the proposed use of SFTs, specifically made from bismuth strontium calcium copper oxide (BSCCO), allows these valves to achieve a bi-stable state. This means that the valve can remain in either the "open" or "closed" position without the need for continuous power, which is particularly beneficial for long-duration operations in cryogenic environments.
The document highlights that the SFTs can maintain a constant magnetic field until a pulsed current is applied to change the state of the valve. This capability enables the selection of intermediate states for flow regulation, allowing for precise control over the flow of cryogenic fluids. The advantages of using SFTs include low heat leakage, minimal thermal hysteresis, and functionality at the low temperatures required for cryogenic applications.
The design of these magnetostrictive valves is described as normally closed (energize-for-flow), meaning they require power to open. The transition to using SFTs not only simplifies the operation but also enhances the utility of the valves in various applications, such as closed-loop control systems and dilution refrigerators.
The document also notes that the magnetostrictive materials used in these valves can operate effectively within a magnetic range suitable for the intended applications. The anticipated reduction in size of the SFTs further increases their applicability in compact cryogenic systems.
Overall, the work represents a significant advancement in the field of cryogenic technology, providing a more efficient and reliable method for controlling fluid flows in extreme conditions. The research was conducted at NASA's Jet Propulsion Laboratory and is positioned as a novel approach with no prior publications on the use of SFTs in magnetostrictive valves. This innovation could lead to improved performance and reliability in future cryogenic devices and systems.
