Displacer for a cryocooler

Abstract

A displacer 12 of a second stage cold head 10 of a cryocooler, comprises a displacer element 30 movable in an internal volume 16 of the cold head, wherein the displacer element comprises an outer surface 26, and is at least partially covered by a heat-shrink tube 28. The heat shrink tube may be pre-stretched thermoplastic, PTFE or FEP and may be glued (32, fig 3) to the outer surface of the displacer element. The displacer element may be made from stainless steel, PEEK or phenolic cotton compound. The outer surface of the displacer element may comprise a roughened surface. The outer surface of the heat shrink tube may comprises grooves ripples, patterns or perforations (figs 4A – 4G) or may comprise separate sections (fig 6). The cryocooler may comprise a cryopump and method of fabricating a displacer for a cryopump is described. .

Claims

1. Displacer for a cryocooler, in particular a second stage of a cold head, comprising:a displacer element movable in an internal volume of a cold head, wherein the displacer comprises an outer surface,wherein the outer surface of the displacer element is at least partially covered by a heat-shrinked tube.

2. Displacer according to claim 1, wherein the heat-shrinked tube is made of heat treated pre-stretched thermoplastic, preferably PTFE or FEP.

3. Displacer according to claim 1 or 2, wherein between the heat-shrinked tube and the outer surface of the displacer element is a glue.

4. Displacer according to any of claims 1 to 3, wherein the thickness of the heat-shrinked tube is below 1mm, preferably below 0.5mm and more preferably below 0.25mm.

5. Displacer according to any of claims 1 to 4, wherein the displacer is made from stainless steel, PEEK, or phenolic cotton compound.

6. Displacer according to any of claims 1 to 5, wherein the heat-shrinked tube comprises fibers for fiber reinforcement and / or one or more additives, such as a lubrication additive, a gluing additive or a thermal stabilizer additive.

7. Displacer according to any of claims 1 to 6, wherein the outers surface of the displacer element comprises a surface roughness (Ra) of 0.2 or larger and preferably 0.5 or larger.

8. Displacer according to any of claims 1 to 7, wherein the outer surface of the heat-shrinked tube comprises grooves, ripples, or patterns.

9. Displacer according to any of claims 1 to 8, wherein the outer surface of the heat-shrinked tube is roughened.

10. Displacer according to any of claims 1 to 9, wherein the heat-shrinked tube comprises perforations.

11. Displacer according to any of claims 1 to 10, wherein the heat-shrinked tube is built as mesh.

12. Displacer according to any of claims 1 to 11, wherein the heat-shrinked tube comprises separate sections arranged along the displacer.

13. Displacer according to any of claims 1 to 12, further comprising a sealing element extending through a respective opening of the heat-shrinked tube.

14. Cryocooler comprising a cold head comprising a cylinder and a displacer according to any of claims 1 to 13 disposed in the cylinder15. Cryopump comprising a cryocooler according to claim 14.

16. Method for fabricating a displacer for a cryocooler, in particular of a cryopump, includingProviding a displacer element having an outer surface;Inserting the displacer element into a heat-shrink tube;Heat treatment of the heat-shrinking tube to reduce the size of the heatshrinking tube to cover at least partially the outer surface of the displacer element.

17. Method according to claim 16, including the step of machining an outer surface of the heat-shrinked tube.

18. Method according to claim 16 or 17, including the step of patterning or roughening the outer surface of the heat-shrinked tube.

19. Method according to any of claims 16 to 18, including the step of applying a glue between the outer surface of the displacer element and the heat-shrinked tube.19

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