3k cold head regenerator design

Abstract

A cryocooler cold head regenerator having a series of discrete sections formed from particles of tin-antimony, particles of holmium copper, particles of gadolinium oxysulfide, and particles of gadolinium aluminate. Each section is separated from an adjoining section by a multi-layer screen formed from a stacked layers of copper mesh, felt, phosphor bronze mesh, and brass mesh. A cryocooler outfitted with regenerator can have an increased heat capacity to achieve temperatures in the cold head below 2.3 K with optimized heat lift at 3 K.

Description

TITLE3K COLD HEAD REGENERATOR DESIGNBACKGROUND OF THE INVENTION1. FIELD OF THE INVENTION

[0001] The present invention relates to cryocoolers and, more specifically, a cold head regenerator design that can achieve a temperature below 2.3 K and optimized cooling performance at 3 Kelvin.2. DESCRIPTION OF THE RELATED ART

[0002] The quantum computing and dilution refrigerator (DR) market is growing very rapidly, and development of high cooling capacity, ultra-low vibration, fast cool-down, energy efficient, and reliable cryocoolers for this market is of great importance. Higher cooling capacities are normally required at 3 K or below, rather than at 4.2 K, for most dilution refrigerators. Commercial 4 K cryocoolers (either Pulse Tube or G-M) are normally designed for optimum performance at 4.2 K. As the performance of the equipment used in applications such as these can be highly dependent on the temperature and the amount of cooling, there is a need for a cryocooler that can provide for temperatures below 2.3 K with improved cooling capacity and performance at 3K.BRIEF SUMMARY OF THE INVENTION

[0003] The present invention comprises a regenerator design for a cryocooler that can achieve temperatures of at least 2.3 K and optimized cooling performance at 3 K. The design comprises the use of four sections of different particles separated by a series of multi-layer screens. The four sections house tin-antimony particles, holmium copper particles, gadolinium oxysulfide particles, and gadolinium aluminate particles. The multi-layer screens are each formed by adjacent layers of copper mesh, fibrous mesh, phosphor bronze mesh, another layer of fibrous mesh, and a final layer of brass mesh. The particle compositions andmulti-layer screens allow compressed helium to more efficiently cool the head of a cryocooler outfitted with a regenerator according to the present invention, thereby allowing the cryocooler to achieve temperatures below 2.3 K and optimized cooling performance at 3K.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0004] The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

[0005] FIG. l is a cross-section of a tubular cold head regeneration chamber showing a design for a regeneration chamber according to the present invention.

[0006] FIG. 2 is a graph of the cooling capacity curves of the 2nd stage of a cryocooler second stage outfitted according to the present invention.

[0007] FIG. 3 is a graph of the cool-down curves of cryocooler having a second stage regeneration chamber according to the present invention operating at 60 Hz.DETAILED DESCRIPTION OF THE INVENTION

[0008] Referring to the figures, wherein like numerals refer to like parts throughout, there is seen in FIG. 1 a tubular regeneration chamber 10 for use in the cold head 24 of a cryocooler 26 according to the present invention that has increased heat capacity to achieve temperatures in the cold head below 2.3 K with optimized heat lift at 3 K. Regenerator chamber 10 comprises a first section 12 containing a first regeneration material, a second section 14 containing a second regeneration material, a third section 16 containing a third regeneration material, and a fourth section 18 containing a fourth regeneration material. Each of first section 12 and second section 14, second section 14 and third section 16, and third section 16 and fourth section 18 are separated by a multi-layer screen 20 that is interposed therebetween. Multi-layer screen 20 assists with rectification of the refrigeration fluid. Thespecific compositions of the first, second, third and fourth regeneration materials as well as the composition and arrangement of multi-layer screen 20 allow regeneration chamber 10 to achieve temperatures below 2.3 K with increased cooling capacity at 3 K when used with compressed helium. As seen in FIG. 1, regeneration chamber 10 may be positioned in a tubular housing 22 for use as a second stage regenerator in the cold head 24 of a cryocooler 26 to provide a cooling capacity of at least 1 Watt at 3 K when under load.

[0009] Referring to FIG. 2, a cryocooler second stage outfitted according to the present invention demonstrated a cooling capacity as shown in the graphs. Cool-down curves are seen in FIG. 3, where a constant heating power of 35 W was applied to the 1ststage, while a constant heating power of 0.90 W was applied simultaneously to the 2ndstage during cold head cool-down from room temperature. With heat loads of 35 W and 0.90 W applied to the 1ststage and 2ndstage simultaneously, it took about 85 minutes for the 1ststage to reach 35 K and about 60 minutes for the 2ndstage to reach 3.0 K. As conventional designs provide a cooling capacity of 0.5 Watts at 3 K under load, regeneration chamber 10 represents a significant improvement in the heat lift of a cryocooler outfitted according to the present invention as the present invention provides for a doubling of the cooling capacity as compared to existing designs.

[0010] First regeneration material of first section 12 may comprise tin-antimony (Sn- Sb) particles. The tin-antimony particles are preferably spherical and have a Sn:Sb composition of approximately 95:5 and a sphere diameter of 0.25 millimeters ± .03 millimeters. Second regeneration material of second section 14 may comprise non-oxidized holmium copper (HoC ) spherical particles with a diameter of approximately 0.15 to 0.445 millimeters. Third regeneration material of third section 16 may comprise gadolinium oxysulfide (Gd2ChS or GOS) particles that are preferably spherical and have a diameter of approximately 0.15 to 0.35 millimeters. Fourth regeneration material of fourth section 18may comprise gadolinium aluminate (GdAlCh or GAP) particles that are preferably spherical and have a diameter of approximately 0.15 to 0.35 millimeters.

[0011] Multi-layer screen 20 comprises a series of layers that provide for flow optimization between first section 12, second section 14, third section 16, and fourth section 18. As an example, multi-layer screen 20 may comprise five layers, namely a first layer 32, a second layer 34, a third layer 36, a fourth layer 38, and a fifth layer 40. At least one layer of first layer 32, second layer 34, third layer 36, fourth layer 38, and fifth layer 40 comprises a non-conductive (thermally) material having a randomized flow channels extending vertically and horizontally therethrough to be permeable to the flow of refrigeration fluid. In some embodiments, more than one layer of first layer 32, second layer 34, third layer 36, fourth layer 38, and fifth layer 40 comprises a non-conductive (thermally) material. For example, first layer 32 may be one or more copper screens, second layer 34 may be a non-woven fibrous mesh pad, third layer 36 may be one or more phosphor bronze mesh screens, fourth layer 38 may be another mesh pad, and fifth layer 40 may be one or more brass screens.

[0012] As an example, the non-conductive material having the randomized flow channels may comprise a non-woven fibrous mesh pad, such as felt, that is comprised of fibers that are felted, matted, or interlocked with a random orientation. As an example, wool felt having a thickness of approximately one-eighth to one-sixteenth of an inch, a wool felt grade of Fl, and a density of 2.00 pounds per square yard is suitable. Alternatively, a felt pad having a thickness ranging from 1 / 16 inches to 1 / 2 inches, a density ranging from 0.1 to 10 pounds per square yard, and a felt pad packing number ranging from 0 to 8 may be used. The non-conductive material be formed from fibers other than wool, including other natural fibers such as cotton or hemp, as well as artificial fibers such as those formed from polymers. Non- conductive material provides rectification of the flow of the cooling fluid, such as helium, by distributing the flow of regeneration fluid vertically and horizontally across regenerationchamber 10 so that the flow through regeneration chamber 10 is more uniform, i.e., transversely and longitudinally within regeneration chamber 10. As a result, other material pads having randomized flow channels extending vertically and horizontally therethrough that provide the same rectification vertically and horizontally across regeneration chamber 10 may be used.

[0013] The remaining layers of multi-layer screen 20 may be comprised of metal or metallic screens formed from aluminum, bronze, phosphor bronze, brass, copper and the like. For example, 24-mesh copper screen formed from copper wire having a diameter of 00.46 millimeters may suffice. Alternatively, the other of first layer 32, second layer 34, third layer 36, fourth layer 38, and fifth layer 40 may be formed from mesh ranging from 2 to 60 mesh with the material comprising copper, stainless steel, or brass. For example, 200 mesh phosphor bronze screen formed from phosphor bronze wire having a diameter of 00.0021 inches (0.05 mm) with an overall opening percentage of 33 percent may be used.Alternatively, a phosphor bronze screen of between 80 and 400 mesh or a 60-mesh brass screen formed from brass wire having a diameter of 00.25 millimeters may be used.Whichever of first layer 32, second layer 34, third layer 36, fourth layer 38, and fifth layer 40 that are not formed from the non-conductive material may have a quantity of 1 to 50 screens of these sizes and metals.

[0014] It should be recognized by those of skill in the art that additional rectification layers may be used depending on the design of regeneration chamber 10 and the materials used therein. In addition, rectification layers may be used in different locations and with different or less combinations of rectification materials, provided that the same degree of rectification is achieved and that regeneration chamber 10 can still deliver at least 1 W of cooling capacity at 3 K in certain cryocoolers and significantly improved cooling capacity in other designs.

Claims

CLAIMSWhat is claimed is:

1. A regenerator for a cryocooler, comprising: a first section comprised of an amount of tin antimony particles; a second section comprised of an amount of holmium copper particles; a third section comprised of an amount of gadolinium oxysulfide particles; a fourth section comprised of an amount of gadolinium aluminate particles; and a series of multi-layer screens positioned between the first section and the second section, the second section and the third section, and the third section and the fourth section, wherein each of the multi-layer screens includes at least one layer formed from a non- conductive material having a plurality of randomized flow channels.

2. The regenerator of claim 1, wherein the non-conductive material comprises a non-woven fibrous mesh pad.

3. The regenerator of claim 2, wherein the non-woven fibrous mesh pad is formed from an amount of felt.

4. The regenerator of claim 3, wherein the amount of felt is wool.

5. The regenerator of claim 3, wherein the amount of felt has a thickness of one- sixteenth inch to one-half inch.

6. The regenerator of claim 5, wherein the amount of felt of the non-woven fibrous mesh pad has a grade of Fl.

7. The regenerator of claim 6, wherein the amount of felt has a density of between 0.1 and 10 pounds per square yard.

8. The regenerator of claim 7, wherein the amount of felt has a packing number between 0 and 8.

9. The regenerator of claim 2, wherein the amount of gadolinium aluminate particles have an average diameter of between 0.15 and 0.35 millimeters.

10. The regenerator of claim 2, wherein the amount of gadolinium aluminate particles have an average diameter of between 0.20 and 0.25 millimeters.

11. The regenerator of claim 2, wherein each of the series of multi-layer screens includes at least one layer of a metal mesh.

12. The regenerator of claim 11, wherein the metal mesh is formed from a metal selected from the group consisting of aluminum, copper, stainless steel, phosphor bronze, and brass.

13. A method of providing a cryocooler having a cold head that can achieve a temperature below 2.3 K with an optimized heat lift at 3 K, comprising the step of positioning the regenerator of claim 1 in the cold head of the cryocooler.

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