1. Field of the Invention
The invention pertains to the field of apparatus used to maintain constant low temperature. More particularly, the invention pertains to refrigeration and storage apparatus for liquefied gasses.
2. Description of Related Art
Many applications, especially those involving low temperature superconductors, require a supply of extremely cold liquid, such as liquid Helium, to operate. Some devices for these applications, especially those involving highly sensitive sensors, are extremely sensitive to vibration. An example of a vibration-sensitive low-temperature device is a Superconducting Quantum Interference Devices (SQUID), which can detect tiny magnetic signals and need to be cooled to ˜4.2K.
Cryocoolers capable of producing liquid Helium at such low temperatures most often use mechanical displacers (a Gifford-McMahon, or “GM cryocooler”) or pulse tubes (“pulse tube cryocooler”) to generate cooling, often in multiple stages. These reciprocating mechanical displacers or the pulsating gas in the pulse tubes create mechanical vibrations which can disrupt the operation of the sensitive superconducting devices.
Prior art cryocoolers for cooling sensitive low temperature devices relied upon physical contact between the lowest temperature cooling stations of the cryocoolers and the device. While this is efficient from a heat transfer point of view, it permits transfer of vibrations from the operation of the cryocooler to the device, which is undesirable.
The invention is an extra-low vibration cryostat, which incorporates a cryocooler and cryostat to cool and house a vibration-sensitive device, with the cryocooler and cryostat sealed gas-tight to each other, but mechanically isolated, so that vibration from the cryocooler does not affect the device.
The cryostat (23) has a gas-tight chamber or neck (13) for containing the low-temperature liquid helium (He) or other cryogen (12). A heat exchange plate (14) is cooled by the cryogen (12), and in turn cools the device (15) attached to the bottom of the cryostat neck (13). The lower part of neck (13) is surrounded by a radiation shield (16) which limits absorption of heat from the surroundings to the cryogen (12) in the neck (13). The top of the cryostat is capped with a room-temperature flange (19) which is mounted via flexible bellows (18) to a mount (25), mounted upon a stand (24). The flexible bellows (18) mechanically isolates the support (25) from the cryostat (23), so that mechanical vibrations at the support (25) are not transmitted to the cryostat (23), while forming a gas-tight enclosure with the gas-tight neck or chamber (13) of the cryostat (23).
The invention incorporates a cryocooler, which is used to produce the low-temperature liquid Helium (He) or other cryogen for cooling the device (15), The cryocooler is shown as a two-stage pulse-tube type cryocooler. In the pulse-tube cryocooler shown in
The warm end (1) of the cryocooler is mounted on the support (25), and the cold end of the cryocooler extends into the neck (13) of the cryostat.
Cryogen gas from a storage tank (20) is fed through a pressure regulator (21) and hose (22) into the neck (13) of the cryostat (23). The gas is cooled as it passes the first stage tubes (4), (5), (6) and the first stage cooling station (7) and second stage tubes (8) and (9), and condenses into liquid on the condenser (11). The liquid cryogen drips from the condenser (11), and collects in a pool of liquid (12) in the cryostat. Additionally, any cryogen which boils off from the pool (12) due to heat from the device (15) rises up, and is recondensed by contact with the condenser (11), minimizing loss of cryogen or maintain low or zero boil-off.
In order to further minimize heat transfer to the liquid cryogen, the radiation shield (16) is cooled by a cooling station (17). There is a narrow gap between the cooling station (17) and the first stage cooling station (7). The cooling capacity is transferred from the cooling station (7) to the cooling station (17) by convection heat transfer of gas.
The design of the invention minimizes transmission of vibrations to the device (15). There is no direct mechanical contact between the device (15) and the cryocooler's second stage cold station (10) which could transmit vibration. The pulsator (2) (also called a rotary valve) is remotely mounted, with a flexible line connection connecting it to the cryocooler head (1). The cold end of the cryocooler is suspended in the neck (13) of the cryostat (23) without contact between the cold end of the cryocooler and the neck (13) within which it is located. Finally, the cryostat (23) is suspended from its support (25) by the flexible bellows (18), producing a high degree of mechanical isolation between the support (25) and the cryostat (23).
Thus, any vibrations generated by the operation of the cryocooler are almost entirely isolated from the device (15).
It will be understood by one skilled in the art that while the various figures have shown the cryostat of the invention with single- and two-stage cryocoolers of the pulse-tube and Gifford-McMahon types, that the invention is not limited to any particular type of cooler. Three-stage coolers could be used, or cryocoolers of other kinds, within the teachings of the invention.
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.
This application claims one or more inventions which were disclosed in Provisional Application No. 61/057,025, filed May 29, 2008, entitled “LOW VIBRATION LIQUID HELIUM CRYOSTAT”. The benefit under 35 USC §119(e) of the U.S. provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.
Number | Date | Country | |
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61057025 | May 2008 | US |