Annular enclosure provided with an arrangement of recesses or protrusions to reduce mechanical resonance

1. An annular enclosure comprising:

a cylindrical outer shell;

a cylindrical inner shell;

annular end caps which join said outer shell to said inner shell, forming said enclosure; and

a non-random pattern of (a) recesses having a bottom surface made of a material of the annular enclosure and (b) protrusions having a top surface made of the material of the annular enclosure and a wall, made of the material of the annular enclosure, descending from the top surface to the bottom surface, wherein the recesses are located between the protrusions;

wherein said pattern is asymmetrical in all axes, whereby the tendency of the material of the annular enclosure to mechanically resonate is reduced.

2. The annular enclosure according to claim 1 , wherein the pattern of recesses and protrusions is formed in at least one of the end caps.

3. The annular enclosure according to claim 1 , wherein at least one of the following features is asymmetrical in all axes: heights h, widths w, spacing d of the recesses and protrusions that form said pattern.

4. The annular enclosure according to claim 1 , wherein the shapes of the recesses and protrusions are asymmetrical in all axes.

5. The annular enclosure according to claim 4 , wherein the recesses and protrusions are pseudo-randomly shaped.

6. The annular enclosure according to claim 2 , wherein the at least one end cap has a thickness of 1-3 mm.

7. The annular enclosure according to claim 1 , wherein the recesses accommodate a constrained layer of vibration-damping material.

8. The annular enclosure according to claim 1 , wherein the recesses accommodate cable runs or other ancillary equipment.

9. A cryostat for housing a solenoidal superconducting magnet, comprising:

a liquid cryogen vessel for containing liquid cryogen;

an outer vacuum chamber surrounding the liquid cryogen vessel; and

a thermal shield between the liquid cryogen vessel and the outer vacuum chamber, wherein,

each of the outer vacuum chamber and the thermal shield comprises an annular enclosure according to claim 1 ;

the outer vacuum chamber has an end cap comprising protrusions; and

the thermal shield has an end cap comprising protrusions that are complementary to an inner surface of protrusions of the outer vacuum chamber.

10. The cryostat according to claim 9 , wherein, in at least one certain region corresponding to the inner surface of a protrusion of the thermal shield, an internal feature such as a suspension member is located.

11. A cryostat for housing a solenoidal superconducting magnet, said cryostat comprising:

a liquid cryogen vessel for containing liquid cryogen; and

an outer vacuum chamber surrounding the liquid cryogen vessel; wherein,

the outer vacuum chamber comprises an annular enclosure according to claim 1 ; and

said annular enclosure has an end cap comprising a feature as an aspect of the recesses or protrusions, which feature allows the location of ancillary equipment on the end cap.

12. The annular enclosure, or a cryostat, according to claim 1 , wherein the pattern of recesses and protrusions is produced by vacuum moulding or “super plastic forming” at a temperature of about 400° C.

13. The annular enclosure according to claim 1 , wherein at least one of said end caps, said cylindrical outer shell, or said cylindrical inner shell, is formed of a composite material formed over a mould having a pattern of recesses and protrusions that form said pattern of recesses and protrusions in said annular enclosure.

14. The annular enclosure according to claim 13 , wherein the composite material includes a constrained layer to assist in damping mechanical vibrations.

15. The annular enclosure according to claim 1 , wherein the pattern of recesses and protrusions is formed of one of aluminum, titanium, or an alloy of aluminum and titanium.

16. The annular enclosure or cryostat, according to claim 1 , wherein the pattern of recesses and protrusions is formed of one of carbon steel, stainless steel, or a composite material.

17. A cryostat for housing a solenoidal superconducting magnet, the cryostat comprising:

a liquid cryogen vessel for containing liquid cryogen; and

an outer vacuum chamber surrounding the liquid cryogen vessel;

wherein the outer vacuum chamber comprises an annular enclosure comprising:

a cylindrical outer shell;

a cylindrical inner shell;

annular end caps which join said outer shell to said inner shell, forming said enclosure; and

a non-random pattern of (a) recesses having a bottom surface made of a material of the annular enclosure and (b) protrusions having a top surface made of the material of the annular enclosure and a wall, made of the material of the annular enclosure, descending from the top surface to the bottom surface, wherein the recesses are located between the protrusions;

wherein said pattern is asymmetrical in all axes, whereby the tendency of the material of the annular enclosure to mechanically resonate is reduced.

18. The cryostat according to claim 17 , the cryostat further comprising a thermal shield between the liquid cryogen vessel and the outer vacuum chamber, wherein:

at least one of the end caps of the outer vacuum chamber comprises protrusions; and

the thermal shield has an end cap comprising protrusions that are complementary to an inner surface of the protrusions of the outer vacuum chamber.

19. The annular enclosure according to claim 1 , wherein the recesses and protrusions are irregularly shaped, and exhibit variation in the shapes of the recesses and protrusions.