Patent Description:
A number of different thermo-mechanical devices are known for achieving such low temperatures, for example using pressure cycling of helium gas. This may be achieved using, for example, a Gifford-McMahon cooler, wherein high-pressure helium, at a pressure typically between <NUM> and <NUM> bar, is used as the working fluid and a cylinder contains a displacer and regenerator. A mechanical valve connects the cylinder to the gas at low pressure and high pressure alternately, and the displacer is moved in synchronisation with the operation of the valve. Gas expansion takes in heat from the environment at one end of the cylinder, so one end of the cylinder may be referred to as the cold head, and is cooled to a low temperature. However, it is not always convenient to place the specimen directly in contact with the cold head of a thermo-mechanical cooler. Furthermore, a two-stage Gifford-McMahon cooler may be able to cool a specimen to a temperature as low as <NUM>, but it is advantageous for at least some applications to provide a further cooling stage to reach even lower temperatures relatively quickly.

<CIT>describes a cryogenic apparatus in which a first stage of a two-stage Gifford-McMahon cooler is in thermal contact with a copper top plate of a cylindrical intermediate-temperature shield, which also has a base plate. The lower end of the second stage of the Gifford McMahon cooler is in thermal contact with a second, smaller copper top plate of a cylindrical low-temperature shield, which also has a base plate; the intermediate temperature shield being concentric and enclosed within (but spaced-apart from) an outer the low-temperature shield being concentric and enclosed within (but spaced-apart from) an outer cylindrical enclosure and the intermediate-temperature shield being enclosed within (but spaced-apart from) the intermediate-temperature shield. In use, the low-temperature shield is typically at about <NUM>. A gas flow duct extends coaxially through the low-temperature shield and leads to a concentric cylindrical vessel, enclosed within, but spaced-apart from, the low-temperature shield, and containing liquid helium (in use). The cylindrical vessel is in thermal contact with a copper (top) support plate of a cylindrical operating-temperature shield, which also has a base plate. The operating-temperature shield is typically at about <NUM>, in use. Perforations are provided in the top plates of the intermediate-, low- and operating-temperature shields, such that when the outer enclosure is evacuated so, too, are the above-mentioned temperature shields. In use, a specimen to be cooled is mounted within the operating-temperature shield, usually on the underside of the top support plate, and is cooled by heat conduction through the support plate to helium within the cylindrical vessel.

A specimen insertion tube or "probe" extends through the top plate of the enclosure to near the bottom of the enclosure. The specimen insertion tube has a removable lid from which extends a support rod (of poor thermal conductivity) having a specimen support plate at its bottom end, to which a specimen can be mounted.

The thermo-mechanical coolers will, in most cases, produce some vibration, whereas in many cases it is advantageous or necessary to inhibit vibration of the specimen, for example, if it is required to perform high-NA (Numerical Aperture) imaging. For this reason, the thermo-mechanical coolers may be mechanically linked to the rest of the apparatus by a vibration-suppressing linkage, such as an edge-welded bellows of stainless steel or bellows of flexible plastic material.

In the described arrangements, although the specimen does not need to be in direct contact with the cold head and additional cooling is provided to facilitate the <NUM> 'pot' or vessel, the <NUM>, <NUM> and <NUM> 'stages' are all concentric and arranged about a substantially vertical or upright axis (in use), and insertion of the specimen into the <NUM> pot is facilitated (from the bottom or the top, depending on the particular configuration of the apparatus) along the same axis. However, this is not always convenient, and it would be desirable to provide a cryogenic apparatus in which (at least) the operating-temperature vessel can be spaced-apart from the longitudinal axis of a cold head of a thermo-mechanical cooler, such that, for example, the operating-temperature vessel can be conveniently mounted, or otherwise supported, on a separate structure, such as an optical table, and the specimen can be mounted in the operating-vessel from the top, rather than the bottom. It would also be advantageous to provide a cryogenic apparatus wherein a specimen can be introduced into, or removed from, the operating-temperature region of a <NUM> pot, preferably from the top, whilst causing minimal temperature losses, thereby minimising delay and inefficiencies during use.

Aspects of the present invention seek to address at least one or more of these issues.

<CIT> describes a magnet, such as an open or closed magnet, that has a first assembly with at least one superconductive main coil and with a first vacuum enclosure enclosing the main coil(s). A first cryocooler coldhead has a rigid first housing and is generally vertically aligned. A first flexible bellows is vertically aligned, has a first end attached to the first housing of the first cryocooler coldhead and has a second end attached to the first vacuum enclosure of the first assembly.

<CIT> describes a helium cooled superconducting magnet assembly including helium gas recondensing apparatus to return liquid helium to the helium supply includes a cryocooler in a sleeve assembly enabling servicing of the cryocooler during superconducting operation of the magnet assembly.

<CIT> describes a coil unit and a refrigeration unit that are positioned such that a second heat conductive member disposed on an extendible wall of a vacuum container and a fourth heat conductive member disposed on an extendible wall of another vacuum container face each other coaxially. In this state, the coil unit and refrigeration unit are relatively moved to approach each other, and thus the second heat conductive member and fourth heat conductive member come in contact.

In accordance with an aspect of the present invention, there is provided a cryogenic apparatus as defined in claim <NUM>. It comprises:.

The vibration-suppression means may, for example, comprise bellows.

In an embodiment, the cryogenic apparatus may comprise an outer vacuum chamber arrangement comprising a first outer chamber housing said first enclosure with a first circumferential air gap therebetween, a rigid tubular bridge member surrounding said tubular link member with a second circumferential air gap therebetween, and a second outer chamber housing said second enclosure with a third air gap therebetween, wherein the first second and third air gaps together define a fluid flow path, and wherein said thermo-mechanical cooler extends into said first outer chamber which has an evacuation port therein and the apparatus further comprises means for sealing said second outer chamber such that, in use, when air is extracted from said outer vacuum chamber arrangement via said evacuation port and said fluid flow path, a vacuum is created in said first and second enclosures.

In this case, the tubular bridge member may be coupled, via first external vibration-suppressing means, to a first port provided in the first outer chamber; and, optionally, the first outer chamber may comprise a second port and a support arm coupled, at one end via second external vibration-suppressing means, to the second port and, at the other end, to said tubular bridge member at a location along its length.

In an embodiment, the liquid helium delivery assembly may comprise at least one conduit that extends from the thermo-mechanical cooler, through said tubular link member, to said liquid helium containing vessel in said second enclosure. In this case, the liquid helium delivery assembly may comprise two substantially parallel capillaries that extend from said thermo-mechanical cooler, through said tubular link member, to said liquid helium containing vessel; and the liquid helium delivery system may, optionally, comprise a needle valve assembly between each of said capillaries and said thermo-mechanical cooler.

In an embodiment, the cryogenic apparatus may further comprise a generally cylindrical end cap having an opening at one end and being coupled at the other end, via fourth vibration suppressing means, to a fourth port of said connecting device.

In an embodiment, the thermo-mechanical cooler may comprise a two-stage thermo-mechanical cooler, wherein the first enclosure is coupled to a first stage if the thermo-mechanical cooler and the liquid helium delivery assembly is coupled to a second stage of said thermo-mechanical cooler.

The first and second enclosures may beneficially define intermediate-temperature shields and a first plate may be provided over the liquid helium containing vessel to define an operating-temperature region for receiving a sample or specimen, in use.

In an embodiment, the cryogenic apparatus may further comprise a second plate thermally coupled to said second enclosure and proximate to said first plate. The apparatus may, optionally, further comprise a cover for removably covering said first and second plates, in use, and providing an air-tight seal with the second enclosure.

In an embodiment, the cryogenic apparatus may further comprise a removable probe assembly configured to be removably mounted over said second enclosure with an air-tight seal therebetween, the probe assembly comprising a housing configured at one end to provide said air-tight seal and provided, at the other end, with an opening for receiving a probe, in use, for introducing a sample into, or removing a sample from, an operating temperature region proximate to said liquid containing vessel.

In an embodiment, the housing may comprise an elongate, generally tubular member and the probe arrangement may further comprise a tubular duct that extends longitudinally through and along the length of the housing with an annular space defined between the tubular duct and the inner surface of the housing, the distal end of said tubular duct configured to be thermally coupled to said liquid helium containing vessel, in use. The apparatus may, optionally, comprise a first outer chamber within which said first enclosure is located, a second outer chamber within which said second enclosure is mounted and a rigid tubular bridge surrounding said tubular link member, the first and second outer chambers being coupled together by said rigid tubular bridge member and a fluid flow path being defined between said first and second outer chambers via an annular space between said tubular link member and the inner surface of the rigid tubular bridge, wherein, when said housing is mounted and sealed over said second outer chamber, said annular space is in fluid communication with said fluid flow path such that, in use, when air is extracted at the first outer chamber, the first and second outer chambers and the annular space between the tubular duct and the housing is evacuated.

In an embodiment, the apparatus may comprising an elongate probe configured to extend into said tubular duct through said opening, the probe comprising a plurality of spaced apart baffles of substantially equal diameter to the inner diameter of the tubular duct.

An isothermal shield may, beneficially, be provided around an end of the tubular duct nearest the end configured to provide said air-tight seal, the isothermal shield comprising a tubular sheath around said tubular duct and having a thermal link to said tubular duct at one end and being configured to be thermally coupled to said second enclosure, in use.

A gas curtain assembly may, optionally, be mounted around said opening, said gas curtain assembly being configured to introduce helium gas into said housing so as to prevent ingress of air to the sample space.

At least one viewing window may, beneficially, be provided in each of the isothermal shield and the tubular duct, near the second enclosure, when in use, the viewing windows being horizontally aligned when the apparatus is oriented for use, such that a specimen mounted on the probe within the tubular duct can be viewed.

In an embodiment, the probe may comprise a conductor housing at its distal end, the conductor housing including one or more wiring ports configured to enable diagnostic wiring to be connected thereto, in use.

These and other aspects of the invention will be apparent from the following Detailed Description.

Embodiments of the present invention will now be described, by way of examples only, and with reference to the accompanying drawings, in which:.

Directional descriptors, such as upper, lower, left, right, clockwise, anti-clockwise, front, rear and other similar adjectives are used for clarity and refer to the orientation of the invention as illustrated in the drawings; however, it will be clear to those skilled in the art that the invention may not always be oriented as illustrated and the invention is not intended to be limited in this regard.

Referring to <FIG>, <FIG> of the drawings, a cryogenic apparatus <NUM> comprises a cryocooler assembly <NUM> and an operating-temperature assembly <NUM>, coupled together by a rigid bridge <NUM>. The cryocooler assembly <NUM> comprises a cylindrical enclosure <NUM> with a base plate <NUM> which couples the enclosure to a support structure comprising, in this case, four elongate, rigid legs <NUM>. The cylindrical enclosure <NUM> also comprises a cylindrical wall <NUM> and a top plate <NUM>. Mounted on the top plate <NUM> is a two-stage cryocooler <NUM>, and the top plate <NUM> is also provided with a port (not shown) so the enclosure <NUM> can be evacuated.

Referring additionally to <FIG> of the drawings, within the enclosure <NUM>, the lower end of the first stage of the two-stage cryocooler <NUM> is in thermal contact with a copper plate <NUM> which forms part of a cylindrical intermediate-temperature shield <NUM> with a thin cylindrical wall <NUM> and a base plate <NUM>, the intermediate-temperature shield <NUM> being spaced-apart from, and enclosed within, the enclosure <NUM>.

A pair of parallel, spaced-apart link intermediate-temperature link plates <NUM> extend downward from the lower surface of the copper top plate <NUM> to a base plate <NUM>. Thus, the link plates <NUM>, which are thermally coupled to the top plate <NUM> that is in thermal contact with the first stage of the cryocooler <NUM>, act as intermediate-temperature links between the first stage of the cryocooler <NUM> and an intermediate-temperature (copper) shield <NUM> within the bridge <NUM>, as will be described in more detail hereinafter.

An intermediate wall <NUM> extends between the intermediate-temperature link plates <NUM> (parallel to, and longitudinally spaced apart from, the base plate <NUM>) to define an upper region <NUM> and a lower region <NUM>. Referring also to <FIG> of the drawings, a four- (or even six-) way cross fitting <NUM> is mounted in the lower region <NUM> and a gas flow duct <NUM> extends from a first port 405a of the cross fitting <NUM>, coaxially within the lower region <NUM> between the link plates <NUM>, through an opening <NUM> in the intermediate wall <NUM>, coaxially within the upper region <NUM> and out through an opening <NUM> in the top plate <NUM>, terminating in an outlet duct <NUM> connected to the 'upper' end of the gas flow duct <NUM> by means of an elbow joint <NUM>. The gas flow duct can be selectively opened and sealed to, respectively, allow and prevent gas flow therethrough. As shown in <FIG>, a radiation baffle <NUM> is mounted within the gas flow duct <NUM>.

A first vibration-suppressing means (e.g. bellows) <NUM> is provided at the connection between the gas flow duct <NUM> to the intermediate wall <NUM> which forms the top plate of the lower region <NUM> between the intermediate-temperature link plates <NUM>. A similar vibration-suppressing means (e.g. bellows <NUM> anchors the longitudinally (i.e. vertically) opposite port 405b of the cross fitting <NUM> to the base plate <NUM> at the base of the lower region <NUM> between the intermediate-temperature link plates <NUM>.

One of the orthogonal ports 405c is coupled to a cylindrical end cap <NUM> (see <FIG>) via a third vibration-suppressing means (e.g. bellows) <NUM>. The end cap <NUM> comprises a short coaxial tubular element having a diametric end wall that has a small, off-centre opening 79a therein. The opposite orthogonal port 405d of the cross fitting <NUM> is anchored, via vibration-suppressing means (e.g. bellows) <NUM> to a thermally conductive (e.g. copper) tube <NUM> that is thermally linked to an intermediate-temperature link plate <NUM> by a coaxial set of heat exchange members <NUM>. In this exemplary embodiment, the heat exchange members <NUM> may beneficially comprise a series of flexible braids of a highly thermally-conductive material, such as high purity copper, the braids being arranged in an equi-distant spacing and angularly offset configuration around the end of the thermally-conductive tube <NUM>, as can be seen in <FIG> of the drawings.

Referring additionally to <FIG> of the drawings, the cross fitting <NUM> may have only four ports; or, as shown in <FIG>, there may be two additional ports 405e (only one shown) for connecting other components, such as a sorption pump (not shown) as required, which would be coupled to the respective port 405e of the cross fitting <NUM> via similar vibration-suppressing means (e.g. bellows). It will be understood by those skilled in the art that the vibration-suppressing characteristics of all of the vibration-suppressing means (e.g. bellows) used to couple elements of the apparatus to the cross fitting <NUM>, as described above, will be substantially identical, thereby to act to cancel out any and substantially all vibrations arising from the first and second stages of the cryocooler <NUM> and also from the operating-temperature assembly <NUM> (to be described hereinafter).

Referring back to <FIG> and <FIG> of the drawings, the cylindrical wall <NUM> of the enclosure <NUM> has two outlet ports 502a, 502b. A first outlet port 502b has coupled thereto, via first vibration-suppressing means (e.g. bellows) <NUM>, an elongate outer tube <NUM> that forms the above-mentioned rigid bridge. As shown in <FIG> of the drawings, the arrangement of heat exchange members <NUM> is located adjacent to the first outlet port 502a and the thermally conductive tube forming the above-referenced intermediate-temperature shield <NUM> extends coaxially through the rigid tubular bridge <NUM> with the outer wall of the thermally conductive tube <NUM> being spaced apart from the inner surface of the rigid tubular bridge <NUM> such that an annular space is provided between the two. The thermally conductive tube <NUM> terminates in a (e.g. stainless steel) washer 504a (<FIG>) coupled to a thermally conductive plate <NUM> within an enclosure <NUM> of the operating-temperature assembly <NUM>. As described above, one end of the rigid tubular bridge <NUM> is coupled, via vibration-suppressing means (e.g. bellows) <NUM> to the enclosure <NUM> of the cryocooler assembly <NUM>. The other end of the rigid tubular bridge <NUM> is coupled to (and in fluid communication with) the outer, generally cylindrical enclosure <NUM> referenced above. A generally cylindrical operating-temperature shield <NUM> is provided within the enclosure <NUM>, and comprises a cylindrical wall 45a and a base plate 45b, wherein the above-referenced thermally conductive (e.g. copper) 'top' plate <NUM> is provided across the top of the cylindrical wall 45a, spaced apart from and parallel to the base plate 45b.

The second outlet port 502a of the enclosure <NUM> is coupled to one end of a rigid support arm <NUM> via a similar vibration-suppressing means (e.g. bellows) <NUM>, the other end of the support arm <NUM> being bolted (or otherwise connected) to the rigid bridge <NUM>.

Within the operating-temperature shield <NUM> there is provided a generally cylindrical vessel <NUM> comprising a cylindrical wall <NUM>, extending 'downward' from the copper top plate <NUM>, and a base plate <NUM>. Thus, the thermally conductive top plate <NUM> of the operating-temperature assembly <NUM>, which covers the operating-temperature shield <NUM> and the vessel <NUM>, is thermally coupled to the intermediate-temperature (first) stage of the cryocooler assembly <NUM> via the thermally conductive tube <NUM> and washer 504a, the thermally-conductive tube <NUM> being thermally coupled, at one end, to an intermediate-temperature link plate <NUM> (of the cryocooler assembly <NUM>) and, at the other end, via a thermally conductive washer 504a, to the copper top plate <NUM> of the operating temperature shield <NUM>. The cylindrical vessel <NUM>, in use, contains liquid helium.

Referring back, once again, to <FIG> and <FIG> of the drawings, a needle valve assembly <NUM> is coupled to the low-temperature (second) stage of the cryocooler <NUM>, the needle valve assembly <NUM> being configured to supply liquid helium to the cylindrical vessel <NUM>. Helium is stored (in the cryocooler assembly <NUM>) in a reservoir (not shown) typically at a pressure of about 11kPA (about <NUM> bar) or less, and at about ambient temperature. The helium gas flows through a duct to the inlet of the cryocooler <NUM>; this cools the gas to about <NUM>. The gas then flows through another duct to the second stage of the cryocooler <NUM>, which cools the helium to about <NUM>, so liquid helium emerges from a first fluid supply assembly <NUM>. A second fluid supply assembly <NUM> is thermally coupled to the second stage of the cryocooler <NUM> and the liquid emerging from the first fluid supply assembly <NUM> is split at a tee-joint <NUM> between the first and second supply assemblies <NUM>, <NUM>. Each fluid supply assembly <NUM>, <NUM> includes a respective needle valve 76a, 77a and a narrow duct or 'capillary' 76b, 77b that extends through the off-centre opening 79a in the end cap <NUM> and through the length of the copper tube <NUM> to the operating-temperature assembly <NUM>, both capillaries 76b, 77b terminating within the cylindrical vessel <NUM>. The needle valves 76a, 77a are used to control the outflow of pressurised liquid helium to the capillaries 76b, 77b. The capillaries 76b, 77b run through copper tube <NUM> and, as liquid helium is fed therethrough (under further pressure from the needle valves) to the cylindrical vessel <NUM>, it is cooled further. By way of example, the liquid helium in the cylindrical vessel may be around <NUM>.

This helium flow is brought about by a pump (not shown) which can extract helium gas from a return gas flow via the gas flow duct <NUM>, and supply it to the reservoir. The pressure at the exit of the gas flow duct <NUM> may, for example, be less than 10Pa (about 1mbar) so that the liquid helium in the cylindrical vessel <NUM> evaporates below its normal boiling point, taking its latent heat from its surroundings, and in particular the copper support plate <NUM> (and hence from a specimen placed thereon or in close proximity thereto). The return helium gas flow is by way of the copper tube <NUM> to the gas flow duct <NUM>.

Thus, as explained above, the cylindrical vessel <NUM> (containing liquid helium) is contained within a cylindrical operating temperature shield <NUM> which is typically about <NUM> in use. The operating-temperature shield <NUM> and the vessel <NUM> are provided in a receptacle or 'pot' <NUM>. The copper top plate <NUM> is an intermediate-temperature (e.g. -<NUM>) plate. A second top plate 46a is provided over the cylindrical vessel <NUM> and is an operating-temperature (e.g. ~<NUM>) plate defining the surface or region by or on which a specimen or sample can be placed, in use. A removable cover (not shown) may be provided for covering the sample and receptacle <NUM> in use, and the cover may have 'windows' or viewing ports in its side walls to allow for viewing or imaging of the specimen or sample situated in or on the operating-temperature region.

As described above, the cryocooler <NUM> in this embodiment may be a two-stage Gifford-McMahon cooler, which uses high pressure helium at a pressure typically between 10bar and 30bar as the working fluid, in a closed circuit. The working fluid is provided by one or more external compressors (not shown). Each stage of the cryocooler <NUM> includes a cylinder with a movable displacer and a rotary valve to connect the cylinder alternately to high pressure and low pressure, and a mechanism to move the displacer(s) in synchronisation with the movement of the valve. Such coolers are commercially available products (e.g. Sumitomo Heavy Industries) and their details are not the subject of the present invention. Since the cryocooler <NUM> includes moving parts which operate typically at a frequency of about <NUM>, the components that are subject to oscillation are isolated from the rigid bridge <NUM> by the respective arrangements of vibration-suppressing bellows <NUM>, <NUM> and <NUM>, <NUM>, <NUM>, <NUM> at the outlet ports 502a, 502b of the enclosure <NUM> and the ports 405a, 405b, 405c, 405d of the cross fitting <NUM> in the lower region <NUM> between the intermediate-temperature link plates <NUM>. In use, liquid helium from the second stage of the cryocooler <NUM> is fed (via the capillaries 76b, 77b) to the cylindrical vessel <NUM> within the operating-temperature shield <NUM> of the receptacle or 'pot' <NUM>. The copper tube <NUM> running through the rigid bridge <NUM> is thermally linked to the intermediate-temperature (e.g. <NUM>) link plates <NUM> such that it acts as an intermediate-temperature shield within the bridge <NUM>. The return helium gas flow (described above) is via the same copper tube <NUM>, which acts to help to maintain the temperature of the shield provided by the copper tube <NUM> such that no additional cooling thereof is required. Any vibration from the pump (not shown) in the operating-temperature assembly <NUM> is suppressed at the vibration-suppressing means <NUM> between the copper tube <NUM> and the port 405d of the cross fitting <NUM>. Helium gas thus returned can be fed back to the second stage (not directly) of the cryocooler <NUM>, which cools the helium to about <NUM> (liquid helium) and it can be fed back through the needle valve assembly <NUM> and capillaries 76b, 77b to the cylindrical vessel <NUM> in the operating-temperature assembly <NUM>. A superconducting magnet can be incorporated in the sample plate 46a in some embodiments.

In use, and with the cover removed from the <NUM> receptacle <NUM>, a specimen or sample may be placed on or near the copper top plate 46a and the cover (not shown) replaced such that there is an air tight seal between the cover and the receptacle <NUM>. Then, the apparatus can be commissioned; first, by evacuating the enclosure <NUM>, thereby evacuating the intermediate-temperature shield <NUM> and the intermediate-temperature shield <NUM> (via the bridge <NUM>) and then starting the cooling process described above using the two-stage cryocooler and the liquid helium delivery system. In order to remove the specimen or sample, the cooling is switched off and the system warmed up. The cover can then be removed (thereby breaking the vacuum) and the sample or specimen accessed.

Referring back to <FIG>, and additionally <FIG> and <FIG>, in an alternative embodiment, there is provided a novel probe arrangement for use with the <NUM> pot described above (instead of the above-referenced cover). The probe arrangement <NUM> is particularly advantageous because it enables a sample or specimen to be introduced into the operating-temperature (~ <NUM>) region within the <NUM> pot <NUM> without having to warm up the system. The probe arrangement <NUM> comprises a cylindrical/tubular housing <NUM> that can be (removably) mounted on the enclosure <NUM> to provide an air-tight seal therebetween, such that the housing <NUM> defines an outer vacuum chamber (OVC) that is evacuated along with the intermediate-temperature shield <NUM> and the intermediate-temperature shield <NUM> when the apparatus is in use. The OVC <NUM> is of greater diameter at the bottom end (to match and accommodate the diameter of the <NUM> receptacle <NUM>) than at the top end. At the top end of the OVC <NUM>, there is provided a gas curtain assembly <NUM> including an inlet port <NUM> and a pressure gauge <NUM> (see <FIG>). The gas curtain assembly <NUM> narrows to a small opening <NUM> through which a (e.g. carbon fibre) probe <NUM> extends, as will be described in more detail hereinafter.

The 'lower' portion of the OVC <NUM> having a larger diameter includes viewing ports <NUM>. Within the OVC <NUM>, there is a tubular duct <NUM> that extends concentrically and longitudinally through the OVC <NUM> and is in thermal communication at its 'bottom' end with the operating temperature (~<NUM>) support plate 46a. An intermediate-temperature shield <NUM> is mounted around the 'lower' end of the duct <NUM>, with the lower end 922a being of a diameter substantially equal to the intermediate-temperature (~<NUM>) plate <NUM> and being bolted (or otherwise affixed) thereto such that they are thermally coupled. The intermediate-temperature shield <NUM>, which may, for example, be formed of thin copper, narrows along its length and terminates about half way up the length of the duct <NUM>. The lower, larger diameter portion of the intermediate-temperature shield <NUM> has viewing ports <NUM>, wherein the viewing ports <NUM> of the OVC <NUM> and the viewing ports <NUM> of the intermediate-temperature shield <NUM> are aligned with similar viewing ports in the duct <NUM> to provide a clear optical path such that viewing or imaging of a sample located in the <NUM> region is facilitated. There is a thermal link <NUM> between the upper edge portion of the tubular intermediate-temperature shield <NUM> and the adjacent outer surface of the duct <NUM>. Helium gas can be pumped into the OVC <NUM> via the inlet port <NUM> of the gas curtain assembly <NUM> to lower the temperature therein. The intermediate-temperature shield <NUM> acts as a "thermal intercept" along the length of the probe arrangement <NUM> such that the temperature in the duct <NUM> is -<NUM> at the 'upper' end (adjacent to the gas curtain arrangement <NUM>) and ~<NUM> at the top of the intermediate-temperature shield <NUM>. Then there is a temperature gradient along the length of the duct <NUM>, within the intermediate-temperature shield <NUM>, from <NUM> at the top of the intermediate-temperature shield <NUM> to ~<NUM> at the operating temperature support plate 46a. This is highly efficient, especially when inserting a specimen into, or removing a specimen from, the operating-temperature region of the <NUM> pot <NUM>, as described below.

A probe <NUM> is provided with a series of concentric baffles <NUM>, spaced apart long its length, and a sliding seal flange <NUM> is provided close to the top of the probe <NUM> (when oriented for use). A conductor housing <NUM> is provided at the proximal (top) end of the probe <NUM> and a specimen mounting plate <NUM> is provided at the opposing distal (bottom) end. The conductor housing may include a number of wiring ports <NUM> to enable diagnostic wiring (and the like) to be connected. The gas curtain arrangement <NUM> incorporates a gas relief valve <NUM> and, in use, when the enclosure <NUM> is evacuated, so too is the operating-temperature assembly (via the tubular bridge <NUM>). In use, the gas relief valve <NUM> can be used to release the vacuum and allow the probe to be removed from and inserted into the housing <NUM> so as to mount or remove a specimen relative to the support plate 46a, without having to stop and warm up the entire apparatus every time.

Referring to <FIG> of the drawings, a clamp <NUM> may be provided, the clamp <NUM> being pivotally mounted to one end of a support arm <NUM>, and the other end of the support arm <NUM> being pivotally coupled to the base plate <NUM> of the apparatus <NUM>. Referring additionally to <FIG> and <FIG>, the <NUM> sample chamber <NUM> can be mounted on, for example, an optical table at a variety of locations, using the pivoting clamp arrangement to brace the support arm <NUM>. It will be appreciated that this is facilitated by the fact the <NUM> sample chamber can be physically separated from the rest of the apparatus because the vibration is isolated within the rest of the apparatus by the balanced internal bellows arrangement <NUM>, <NUM>, <NUM>, <NUM> (in the lower region <NUM> between the intermediate-temperature link plates <NUM>) and the balanced external bellows arrangement <NUM>, <NUM>. The novel probe arrangement <NUM> enables the <NUM> sample chamber to be loaded from the top, which is much more convenient, without completely decommissioning the apparatus and warming all the elements up.

Claim 1:
A cryogenic apparatus (<NUM>) comprising:
a first enclosure (<NUM>);
a thermo-mechanical cooler (<NUM>) thermally coupled to said first enclosure (<NUM>);
a second enclosure (<NUM>) spatially distanced from the first enclosure (<NUM>);
an elongate tubular link member (<NUM>) configured to thermally couple the first and second enclosures across the space between them;
a liquid helium containing vessel (<NUM>) located in or proximal to said second enclosure (<NUM>) for holding liquid helium, in use;
a liquid helium delivery assembly (<NUM>, <NUM>) for delivering helium from said thermo-mechanical cooler (<NUM>) to said liquid helium containing vessel (<NUM>);
a helium gas extraction duct (<NUM>) for carrying helium gas returned from said second enclosure (<NUM>), via said link member (<NUM>), to said thermo-mechanical cooler (<NUM>);
a connecting device (<NUM>) located in said first enclosure (<NUM>) and comprising a plurality of fluidly coupled ports (405a-c), wherein a first port (405a) of said connecting device (<NUM>) is coupled, via first vibration-suppressing means (<NUM>), to an end of said tubular link member (<NUM>), a second port (405b) of said connecting device (<NUM>) is coupled, via second vibration-suppressing means (<NUM>), to an end of said helium gas extraction duct, and a third port (405c) of said connecting device (<NUM>) is coupled, via third vibration suppressing means (<NUM>), to a wall of said first enclosure (<NUM>).