CRYOSTAT FOR OPERATION WITH LIQUID HELIUM AND METHOD OF OPERATING THE SAME

Abstract

A cryostat for operation with liquid helium, may comprise a primary chamber with a main region and a pot region for containing a bath of liquid helium-4, primary inlet means for introducing liquid helium-4 and primary outlet means for releasing gaseous helium-4, the primary inlet means comprising a transfer line extending into the primary region. The cryostat may be configured for operation under a continuous supply of liquid helium-4 and at a reduced helium-4 pressure, whereby gaseous helium-4 is pumped off through the outlet means. The primary chamber may comprise a baffle structure arranged between the pot region and the main region, the baffle structure defining at least one flowpath for the flow of gaseous helium-4, each flowpath forming a detoured connection between the pot region and the main region.

Claims

1-25. (canceled)

26. A cryostat for operation with liquid helium, comprising: a primary chamber comprising a main region and a pot region configured to contain a bath of liquid helium-4; a primary inlet configured for introduction of the liquid helium-4, the primary inlet comprising a transfer line extending into the primary chamber; a primary outlet configured for release of gaseous helium-4; and a baffle structure disposed in the primary chamber between the pot region and the main region, the baffle structure defining at least one flowpath for flow of the gaseous helium-4, wherein the cryostat is configured for operation under a continuous supply of the liquid helium-4; wherein the cryostat is configured for operation at a reduced pressure of the gaseous helium-4, whereby the gaseous helium-4 is pumped off through the primary outlet; and wherein the at least one flowpath forms a detoured connection between the pot region and the main region.

27. The cryostat according to claim 26, wherein the baffle structure comprises a heat exchanging region with a heat exchanging area.

28. The cryostat according to claim 27, wherein a ratio of the heat exchanging area to an average liquid/gas surface area in the pot region is at least 1.

29. The cryostat according to claim 26, wherein the baffle structure comprises at least one spiraled surface leading from the pot region to the main region of the primary chamber.

30. The cryostat according to claim 26, wherein the baffle structure comprises an axial passage for receiving therein the transfer line.

31. The cryostat according to claim 30, wherein the axial passage is formed as a tubular section integrally connected to the baffle structure.

32. The cryostat according to claim 26, wherein the baffle structure, or the primary chamber, or both, are made by a 3D-printing technique.

33. The cryostat according to claim 26, further comprising a radiation shield disposed substantially surrounding at least the pot region of the primary chamber.

34. The cryostat according to claim 33, wherein the radiation shield is coolable by thermal contact with an outer wall portion of the primary chamber.

35. The cryostat according to claim 26, wherein the primary chamber is substantially cylindrical.

36. The cryostat according to claim 26, wherein an external surface of the pot region is configured with a primary attachment member for external attachment of a sample.

37. The cryostat according to claim 26, wherein the primary outlet comprises a coupling member configured for connecting to a helium pumping device.

38. The cryostat according to claim 26, further comprising a secondary chamber configured for operation with helium-3, the secondary chamber comprising a secondary inlet and a secondary outlet for the helium-3.

39. The cryostat according to claim 38, wherein the cryostat is configured for operation at a reduced pressure of the helium-3, whereby gaseous helium-3 is pumped off through the secondary outlet.

40. The cryostat according to claim 38, wherein the secondary inlet comprises a cannular transfer line configured for precooling supplied helium-3 via one or both of: i) a curved section formed to substantially follow a flowpath of the at least one flowpath of the baffle structure; and ii) a meandering or spiraling section formed in the cannular transfer line in a region of the cannula transfer line within the bath of the liquid helium-4.

41. The cryostat according to claim 38, wherein an external surface of the secondary chamber is configured with a secondary attachment member for external attachment of a sample.

42. A method for operating the cryostat of claim 26, comprising: evaporatively cooling the pot region by suppling the liquid helium-4 from a first external reservoir through the primary inlet into the pot region at least until the bath of liquid helium-4 begins to accumulate along a bottom surface of the pot region; and maintaining a temperature of the bath of the liquid helium-4 by regulating the supply of the liquid helium-4, or regulating a rate of the pumping off of the gaseous helium-4 through the primary outlet, or controlling heating of the cryostat, or combinations thereof.

43. The method according to claim 42, wherein the temperature of the bath of the liquid helium-4 is maintained within a range of about 1.4 K to about 1.5 K.

44. The method according to claim 43, wherein the cryostat further comprises a secondary chamber configured for operation with helium-3, the secondary chamber comprising a secondary inlet and a secondary outlet for the helium-3, and the cryostat configured for operation at a reduced pressure of the helium-3, whereby gaseous helium-3 is pumped off through the secondary outlet; and wherein the method further comprises supplying the helium-3 from a second external reservoir through the secondary inlet into the secondary chamber, thereby evaporatingly cooling the secondary chamber at least until a bath of liquid helium-3 is formed, and maintaining a temperature of the bath of the liquid helium-3 by regulating the supply of the helium-3, or regulating a rate of the pumping off of the gaseous helium-3 through the secondary outlet, or both.

45. A method of using the cryostat of claim 26, comprising cooling at least one of a sample, a detector device, a medical scanning device, a superconducting device, an electronic device, and a combustion engine component.

46. A method of using the cryostat of claim 26 for spectroscopy, or diffraction measurements, or electronic property measurements, or combinations thereof.

47. A device configured for being cooled by the cryostat according to claim 26.

48. A sample holder configured for attachment to the cryostat according to claim 26.

49. The sample holder according to claim 48, wherein the sample holder is configured for use for spectroscopy, or diffraction measurements, or electronic property measurements, or combinations thereof.

50. The sample holder according to claim 48, wherein the sample holder is configured for use for cooling at least one of a sample, a detector device, a medical scanning device, a superconducting device, an electronic device, and a combustion engine component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of various embodiments of this invention taken in conjunction with the accompanying drawings, wherein are shown:

[0089] FIG. 1: a first embodiment of a cryostat, in a schematic vertical sectional view;

[0090] FIG. 2: a second embodiment of a cryostat, in a schematic vertical sectional view;

[0091] FIG. 3 a second embodiment of a cryostat, in a schematic vertical sectional view;

[0092] FIG. 4 a fourth embodiment of a cryostat, in a schematic vertical sectional view;

[0093] FIG. 5 a fifth embodiment of a cryostat, in a schematic perspective partially cut away view,

[0094] FIG. 6 a lower part of the cryostat of FIG. 5, in an enlarged representation; and

[0095] FIG. 7 a sixth embodiment of a cryostat, in a schematic perspective view.

DETAILED DESCRIPTION OF THE INVENTION

[0096] The cryostat shown in FIG. 1 comprises a primary chamber 2 with a main region 4 and a pot region 6 containing a bath 8 of liquid helium-4. The latter is confined by a bottom surface 10 of the primary chamber, which in the present example is configured as a cylindrical tube forming a pot at its bottom with inner diameter di and a constant cylinder cross-sectional area of

[00001]$A_{\mathrm{Cyl}}=\frac{\pi }{4}{d}_i^2$

[0097] If the cryostat is operated vertically as shown in FIG. 1, both the average liquid/gas surface area A.sub.S and the average cross-sectional area A.sub.S are equal to the cylinder cross sectional area A.sub.cyl.

[0098] The cryostat also comprises inlet means 12 for introducing liquid helium-4 (denoted as .sup.4He(I)) and outlet means 14 for releasing gaseous helium-4 (denoted as .sup.4He(g)). Typically, the liquid helium-4 is supplied from an external storage container not shown in the figure which is coupled to the inlet means 12. The latter comprise a transfer line 16 extending into the main region 4. In the example shown the transfer line 16 is configured as a thin walled metal tube reaching down to the pot region 6 and ending just above the liquid helium-4 bath 8. Also shown in FIG. 1 are primary attachment means 17 disposed at the bottom of the pot region 6 for holding a sample not shown here.

[0099] In order to allow cryostat operation below 4.2 K under a continuous supply of liquid helium-4 at a reduced helium-4 pressure, gaseous helium-4 continuously evaporating from the bath is pumped off through the outlet means 14 by a suitable pumping system.

[0100] The primary chamber further comprises a baffle structure 18 with a heat exchanging area A.sub.H. In the example of FIG. 1, the baffle structure defines two distinct flowpaths 20a and 20b, respectively, which direct the flow of gaseous helium-4. Each flowpath comprises a spiraled surface leading from the pot region 6 to the main region 4 in a detoured connection. As clearly shown in FIG. 1, there is no direct connection form the surface of the helium-4 bath 8 to the main region 4. One should note that a thin space between the cannular transfer line 16 and the baffle structure 18 is shown with an enhanced distance merely for illustration purposes. In practice, such a space will be either non-existent or so small that no substantial gas flow will occur therethrough. Advantageously, the ratio of heat exchanging area A.sub.H to average cross-sectional area A.sub.S is larger than one. In the example shown in FIG. 1, the baffle structure 18 comprising spiraled surfaces with several turns has a correspondingly large heat exchanging area A.sub.H, and the above-mentioned area ratio is substantially larger than one.

[0101] In an exemplary embodiment, the cryostat main region had an inner diameter of 3 cm, and lengths of 30 and 85 cm have been used. The inner volumes were thus in the order of 5×10.sup.−4 cubic meters. Given that the surface area of the detouring/spiraling shall be larger than the average cross-sectional area of the pot region, the length of the heat exchanging section typically exceeds the length of the pot section. In the exemplary cryostat, the pot region had a height of 4 cm and an inner diameter of 15 mm.

[0102] In the embodiment of FIG. 1, the baffle structure 18 is configured as a separate piece which is longitudinally inserted into the primary chamber 2 before assembly. In contrast, FIG. 2 shows an embodiment in which the baffle structure 18 is integrally formed with the primary chamber 2 by 3-D printing. In other words, every element 22 forming a spiraled surface is in integral connection with a corresponding inner wall region 24 of the primary chamber 2.

[0103] In the embodiment shown in FIG. 3, the cryostat comprises a radiation shield 26 disposed substantially surrounding the pot region 6 of the primary chamber 2. The radiation shield 26 is cooled by thermal contact to an outer wall portion 28 of the primary chamber surrounding the baffle structure 18.

[0104] Also shown in all of the figures is a flange 30 for vacuum tight connection to a vacuum chamber.

[0105] The bottom surface 10 of the primary chamber is typically used for attachment of a sample or other body that shall be cooled.

[0106] FIG. 4 shows a further embodiment wherein the cryostat further comprises a secondary chamber 32 for operation with helium-3, secondary inlet means 34 for helium-3 and secondary outlet means 36 for helium-3. In the example shown, the cryostat is configured for operation at a reduced helium-3 pressure in the secondary chamber 32, whereby gaseous helium-3 is pumped off through the secondary outlet means 36. Specifically, the secondary inlet means 34 comprise a cannular transfer line 38 which is configured for precooling supplied gaseous helium-3 (denoted as .sup.3He(g)) by means of a curved section 40 formed to substantially follow a flowpath of the baffle structure, and by means of a meandering or spiraling section 42 formed in the cannular transfer line in a region thereof within the liquid helium-4 bath. Also shown in FIG. 4 are secondary attachment means 44 disposed at the bottom of the secondary chamber 32 for holding a sample not shown here.

[0107] Constructive examples of cryostats according to the invention are shown in FIGS. 5 to 7. The same reference numerals will be used to indicate features that are identical or functionally equivalent to those discussed in relation to FIGS. 1 to 4.

[0108] A cryostat system for use with helium-4 is shown in FIGS. 5 and 6. As shown in the enlarged view of FIG. 6, the bottom surface 10 underneath the pot region 6 is provided with a sample holder 46 holding a sample 48. The sample holder 46 is attached to the bottom surface 10 through primary attachment means 17 indicated schematically by an arrow. In the example shown, the sample holder 46 comprises a tip part 50 and a base part 52 which is pluggable into a correspondingly configured portion of the primary attachment means 17.

[0109] A cryostat system for use with helium 4 and helium-3 is shown in FIG. 7. The various components shown in the FIG. 7 have already been described in relation to FIGS. 1 to 4. FIG. 7a) shows the entire device, whereas FIG. 7b) shows its lower part in an enlarged view. In order to appreciate the degree of miniaturization achieved, FIG. 7c) shows a part of the primary chamber 2 in an enlarged view together with a 2 EUR coin, indicating that the primary chamber 2 and the complex structure contained therein do not exceed an outer diameter of about 25 mm.

LIST OF REFERENCE NUMERALS

[0110] 2 primary chamber [0111] 4 main region [0112] 6 pot region [0113] 8 liquid helium-4 bath [0114] 10 bottom surface of 2 [0115] 12 primary inlet means [0116] 14 primary outlet means [0117] 16 transfer line [0118] 17 primary attachment means [0119] 18 baffle structure [0120] 20a,b flowpath for gaseous helium-4 [0121] 22 path element of 18 [0122] 24 inner wall region of 2 [0123] 26 radiation shield [0124] 28 outer wall portion of 2 [0125] 30 flange [0126] 32 secondary chamber [0127] 34 secondary inlet means [0128] 36 secondary outlet means [0129] 38 transfer line [0130] 40 curved section [0131] 42 meandering or spiraling section [0132] 44 secondary attachment means [0133] 46 sample holder [0134] 48 sample [0135] 50 tip part of 46 [0136] 52 base part of 46