Co-axial interconnect for low temperature applications

Disclosed is an electrical interconnect for use at cryogenic temperatures, wherein the electrical interconnect has an inner electrical conductor, an electrically insulating layer that substantially surrounds the inner electrical conductor, an outer electrical conductor substantially co-axial with the inner electrical conductor, and a heat transfer element, wherein the heat transfer element has an electrically insulating material, wherein the heat transfer element has a thermal conductivity which is larger than a thermal conductivity of the electrically insulating layer, and wherein the heat transfer element is arranged in an opening in the insulating layer and is configured for thermally connecting the inner electrical conductor with the outer electrical conductor.

BACKGROUND

The invention relates to an electrical interconnect for use in low temperature application, in particular for use at cryogenic temperatures. Furthermore, the invention relates to a cooling system for cooling an electrical interconnect. Furthermore, the invention relates to a method for manufacturing an electrical interconnect for use in low temperature applications. Furthermore, the invention relates to a method for cooling the inner electrical conductor of an electrical interconnect.

For devices that operate at cryogenic temperatures, in particular at temperatures in the milli-Kelvin range or close to absolute zero, it is usually essential that the cooled device continuously remains at said low temperature during operation. For example, in the case of quantum computing devices even a relatively small increase in temperature may result in thermal vibrations that cause a loss of quantum coherence.

Generally, such systems use electrical interconnects such as coaxial cables and/or connectors for transmitting signals between the various components of the device. Coaxial cables typically consist of an inner conductor surrounded by a concentric outer conductor, wherein the two conductors are separated by a dielectric insulating layer that surrounds the inner conductor.

The use of the electrical interconnect however provides a pathway for the transport of heat into and between the attached components of the device. In addition, the electrical interconnect itself can also introduce undesired heat, particular in case the electrical interconnect is not adequately cooled to said very low temperatures. As a result, it is essential that the electrical interconnect itself also is cooled down and remains at said very low temperature.

GB 1,156,428, for example, discloses the use of coaxial tubes, comprising an inner conductor tube which is surrounded by a conductive co-axial tube of the same material, wherein a of electrical insulation layer separates the inner and outer tubes. The coaxial tubes are arranged inside an outer wall frame which is surrounded by thermal insulation. In use, liquid hydrogen is pumped through the center section of the coaxial tubes, thus keeping the inter conductor tube cold, and is returned over the outside of the coaxial tubes through a space between the coaxial tubes and the outer wall frame. Accordingly, both the inner conductor tube and the surrounding conductive co-axial tube are cooled by said liquid hydrogen.

SUMMARY OF THE INVENTION

A disadvantage of the known coaxial electrical interconnects for use at cryogenic temperatures is that cooling of an inner conductor by using a tube shaped inner conductor and pumping liquid hydrogen through said tube shaped inner conductor requires an complex system for handling the cryogenic liquid, for example for injecting said cryogenic liquid in the tube shape inner conductor on one side of the coaxial electrical interconnect and for directing the cryogenic liquid from the center section of the inner conducting to the outer section of the co-axial outer conductor. In addition, the coaxial tubes arranged in an outer wall frame as described in GB 1,156,428 provide a substantially bulky and relatively rigid electrical interconnect. It is noted that without the tube shaped inner conductor, the cooling of the inner conductor is hindered by the thermally insulating nature of the electrical insulating layer which surrounds the inner electrical conductor.

It is an object of the present invention to provide an alternative electrical interconnect that permits cooling of the inner conductor of the electrical interconnect.

According to a first aspect, the invention provides an electrical interconnect for use at cryogenic temperatures, wherein the electrical interconnect comprises:an inner electrical conductor,an electrically insulating layer that substantially surrounds the inner electrical conductor,an outer electrical conductor substantially co-axial with the inner electrical conductor, anda heat transfer element,wherein the heat transfer element comprises an electrically insulating material, wherein the heat transfer element comprises a thermal conductivity which is larger than a thermal conductivity of the electrically insulating layer, wherein the heat transfer element is arranged in an opening in the insulating layer and is configured for thermally connecting the inner electrical conductor with the outer electrical conductor,wherein the electrical interconnect preferably comprises a thermal interface material, wherein the thermal interface material is located between the heat transfer element and the inner electrical conductor.

It is noted that for the proper operation of a co-axial electrical interconnect, it is essential that the layer of material between the inner electrical conductor and the co-axial outer electrical conductor is electrically insulating. It is further noted that electrically insulating materials commonly have a very low thermal conductivity.

De inventor has used the fact that some electrically insulating materials have a relatively high thermal conductivity, and which is used to provide a heat transfer element according to the invention. Examples of such materials are diamond, graphite, silicon and sapphire. The addition of the heat transfer element in the coaxial electrical interconnect provides a local thermal bridge between the outer electrical conductor and the inner electrical conductor.

In addition, the inventor has used the fact that electrically conducting materials, such as the inner and the outer electrical conductor, commonly have a high thermal conductivity. Due to the relatively high thermal conductivity along the inner electrical conductor and along the outer electrical conductor a local thermal bridge is substantially sufficient for cooling a substantial length of the inner electrical conductor of the coaxial electrical interconnect. As a result, the heat transfer element allows cooling of the inner electrical conductor, effectively bypassing the thermally insulating effects of the insulating layer that separates the two electrical conductors.

Furthermore, due to the significantly more accessible arrangement of the outer electrical conductor compared to the inner electrical conductor, the process of cooling the electrical interconnect by applying a heatsink or a cooling medium to the outer electrical conductor, provides a more simplified way of cooling the inner electrical conductor via the outer electrical conductor and the heat transfer element. At the same time, due to the electrically insulating nature of the heat transfer element, the transmission characteristics of the electrical interconnect are substantially unaffected.

In an embodiment, the heat transfer element has a cylindrical shape, preferably a circle-cylindrical shape. The use of a cylindrically shaped heat transfer element allows for more convenient production of the heat transfer element, as the heat transfer element may be produced by for example a hollow-cored drill. Furthermore, the cylindrical-shape allows for a convenient manufacturing of a corresponding opening in the electrically insulating layer and/or the outer electrical conductor that the heat transfer element passes through, for example via drilling.

In an embodiment, a center of the line cylindrically shaped heat transfer element is oriented substantially perpendicularly to a longitudinal axis of the inner electrical conductor. The perpendicular orientation of the center line of the heat transfer element provides for a minimal distance between the inner electrical conductor and the outer electrical conductor, and thus for a minimal length along the center line of the heat transfer element. This decreases the thermal resistance against heat transfer between the inner electrical conductor and the outer electrical conductor via the heat transfer element. Furthermore, such a perpendicular orientation simplifies the process of disposing the heat transfer element in the electrical interconnect.

In an embodiment, the thermal interface material is also located between the heat transfer element and the outer electrical conductor. The placement of the thermal interface material at the interfaces between the heat transfer element and the inner and/or outer electrical conductors respectively, enhances a thermal contact between these elements. Furthermore, the addition of the thermal interface material allows for smoothing out of any geometric defects that may be present on the surfaces of the heat transfer element and the inner and outer electrical conductors, which would otherwise disturb to the heat transfer between these elements.

It is noted that because the thermal interface material is preferably arranged only between the thermal transfer element and the inner electrical conductor and between the thermal transfer element and the outer electrical conductors, respectively, the thermal interface material may be electrically conductive, as no direct electrically conductive path exists between the inner and outer electrical conductors. As a result, a significantly wider range of materials can be used as the thermal interface material.

In an embodiment, the thermal interface material is a thermally conductive adhesive, preferably wherein the thermal interface material is a metal-filled epoxy, most preferably wherein the thermal interface material is a silver-filled epoxy. The use of an adhesive allows for more convenient assembly/production of the electrical interconnect, and ensures that the heat transfer element remains fixedly in place during both transport and use. Furthermore, the use of the metal-filled, or more preferably silver-filled, epoxy allows for a combination of a strong bonding adhesive while allowing for sufficient thermal conductivity of the thermal interface material.

In an embodiment, the amount of metal/silver in said metal-filled epoxy is larger than 70%, preferably larger than 80%. In an embodiment, the silver-filled epoxy comprises 70-95% of silver powder, preferably 90-95% of silver powder. Preferably the above mentioned silver content refers to a volume percentage. Such a large percentage of metal/silver provides a suitable thermal conductivity in combination with adequate adhesive properties to properly retain the heat transfer element.

In an embodiment, the heat transfer element extends a first distance along a direction substantially perpendicular to a longitudinal axis of the inner electrical conductor, wherein the first distance is greater than or substantially equal to a thickness of the insulating layer. By providing a heat transfer element that extends over a length substantially equal to the thickness of the insulating layer, the heat transfer element substantially bridges the distance between the inner conductor and the outer conductor, which enhances the heat transfer and/or reduces the amount of thermal interface material required to provide an adequate heat transfer between the inner conductor and the outer conductor.

In an embodiment, the first distance is smaller than or substantially equal to a sum of the thickness of the insulating layer and a of thickness the outer electrical conductor. Accordingly, the heat transfer element can be arranged to be mounted substantially within the circumference of the outer conductor, providing a substantially smooth outer surface f the electrical interconnect.

In an embodiment, the heat transfer element is fabricated from an aluminum oxide based material, preferably wherein the heat transfer element is fabricated a single crystal sapphire material. The use of from aluminum oxide based materials, and especially single crystal sapphire-based materials, provides a highly beneficial combination of a low electrical conductivity and a high thermal conductivity.

Preferably, the single crystal sapphire material is oriented such that a crystal axis of the single crystal sapphire material with the highest thermal conductivity is oriented perpendicularly to the longitudinal axis of the inner electrical conductor. In particular, the transfer element is configured such that the C-axis direction of the single crystal material sapphire is oriented substantially perpendicular to the longitudinal axis of the inner electrical conductor. This embodiment is advantageous because the thermal conductivity along the C-axis direction of the single crystal sapphire material is approximately 10% higher than in a direction perpendicular to this C-axis direction.

In an embodiment, the outer electrical conductor substantially coaxially surrounds the electrically insulating layer, preferably wherein the electrically insulating layer is configured to substantially fill the space between the inner electrical conductor and the outer electrical conductor.

In an embodiment, the outer electrical conductor comprises CuNi or stainless steel, and/or wherein the inner electrical conductor comprises CuNi or silver plated the isolating layer comprises CuNi, and/or wherein polytetrafluoroethylene (PFTE). The use of a CuNi, or cupronickel, is beneficial due to its combination of good ductility retention, a high electrical and a high thermal conductivity at low temperatures.

In an embodiment, the electrical interconnect comprises an opening, wherein the opening extends between the inner electrical conductor and at least the outer electrical layer, wherein the heat transfer element is arranged in said opening, and wherein the opening is configured such that the physical dimensions of the opening are substantially equal to the physical dimensions of the heat transfer element. Accordingly, a good mechanical fit is provided between the opening and the heat transfer element, which promotes the mechanical stability of the heat transfer element within the opening. Furthermore a good mechanical fit between the heat transfer element and the opening ensures that the heat transfer element substantially closes off the opening.

In an embodiment, wherein the electrical interconnect comprises a heat transfer surface, wherein said heat transfer surface comprises a part of the outer electrical conductor, the heat transfer element and/or the thermal interface material, wherein said heat transfer surface is configured to be thermally connectable with a heatsink or a cooling medium. Providing the outer electrical conductor and/or the heat transfer element, or the thermal interface material arranged to connect the heat transfer element to the outer electrical conductor, with a heat transfer surface allows a user to connect the electrical interconnect, through said heat transfer surface, with a suitable heatsink of cooling medium. This in turn allows for the extraction of thermal energy from the inner electrical conductor, via the heat transfer element and/or the outer electrical conductor, to the heatsink or cooling medium. Preferably, the heatsink or cooling medium is actively cooled to temperatures in the milli Kelvin (mK) range, which in turn allows the inner electrical conductor to also be kept at said temperatures.

In an embodiment, the electrical interconnect is a coax cable, or a SMA, SMP, MCX or MMCX type connector.

In an embodiment, the electrical interconnect comprises two or more heat transfer elements.

In an embodiment, the two or more heat transfer elements are arranged along a circumference of the electrical interconnect, preferably in a plane substantially perpendicular to a longitudinal direction of the electrical interconnect. By arranging two or more heat transfer elements in parallel along the circumference of the electrical interconnect, the heat transfer between the inner electrical conductor and the outer electrical conductor can be enhanced.

In an embodiment, the two or more heat transfer elements are arranged spaced apart, preferably in a direction along a longitudinal axis of the electrical interconnect. By arranging two or more heat transfer elements in parallel along the longitudinal axis of the electrical interconnect, also longer electrical interconnecting cables can be effectively cooled.

According to a second aspect, the invention for cooling an electrical provides a cooling system interconnect comprising the electrical interconnect according to the first aspect of the invention, or an embodiment thereof, and a cryocooler,wherein the cryocooler comprises a heatsink, wherein the cryocooler is configured for actively cooling said heatsink,wherein the heatsink is configured to be placed in thermal contact with the outer electrical conductor of the electrical interconnect,preferably wherein the cryocooler is configured for actively cooling said heatsink to temperatures below 1 K, more preferably temperatures below 100 mK, most preferably below 10 mK.

According to a third aspect, the invention provides a method for manufacturing an electrical interconnect according to the first aspect of the invention, or an embodiment thereof, wherein the method comprises the steps of:providing an electrical interconnect which comprises an inner electrical conductor, an electrically insulating layer that substantially surrounds the inner electrical conductor, an outer electrical conductor substantially co-axial with the inner electrical conductor, and an opening, wherein the opening extends through the insulating layer, and wherein the opening extends from the outer electrical conductor to at least the inner electrical conductor,disposing a heat transfer element in the opening and thermally connecting the heat transfer element with the inner electrical conductor and with the outer electrical conductor in order to thermally bridge the conductor with the inner electrical outer electrical conductor of the electrical interconnect, wherein the heat transfer element comprises an electrically insulating material, wherein the heat transfer element comprises a thermal conductivity which is larger than a thermal conductivity of the electrically insulating layer.

In an embodiment, the method further comprises the step of:applying a first thermal interface material between the inner electrical conductor and the heat transfer element, wherein the step of applying a first thermal interface material is performed before the step of disposing the heat transfer element within the opening.

In an embodiment, the first thermal interface material is a thermally conductive adhesive, preferably wherein the first thermal interface material is a metal-filled epoxy, most preferably wherein first thermal interface material is a silver-filled epoxy.

In an embodiment, the method further comprises the step of:applying a second thermal interface material between the heat transfer element and the outer electrical conductor, wherein the step of applying the second thermal interface material is performed after disposing the heat transfer element within the opening.

In an embodiment, the second thermal interface material is the same as the first thermal interface material.

According to a fourth aspect, the invention provides a method for cooling the inner electrical conductor of the electrical interconnect according to the first aspect of the invention, or any embodiment thereof, via outer electrical conductor and/or the heat transfer element,wherein the method comprises the step providing a heatsink or a cooling medium in thermal contact with the outer electrical conductor and/or the heat transfer element.

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications.

DETAILED DESCRIPTION OF THE INVENTION

FIG.1schematically shows a cross-section of a segment of an electrical interconnect1in the form of a coaxial cable1. The coaxial cable1comprises an inner electrical conductor2that extends along a longitudinal direction L of the coaxial cable1. The coaxial cable1further comprises an electrically insulating layer3, wherein the electrically insulating layer3is concentric with, and substantially surrounds the inner electrical conductor2. Furthermore, the electrically insulating layer3extends along the longitudinal direction L of the coaxial cable1. The electrically insulating layer3extends radially outwards from the inner electrical conductor2. The electrically insulating layer3preferably comprises a dielectric material and has a thickness TINS.

The coaxial cable1further comprises an outer electrical conductor4, wherein n the outer electrical conductor4is concentric with both the inner electrical conductor2and the electrically insulating layer3, wherein the outer electrical conductor4is shown surrounding the electrically insulating layer3. The outer electrical conductor4has a thickness TOC.

As schematically shown inFIG.1, the outer electrical conductor4substantially coaxially surrounds the electrical insulating layer3, wherein the electrical insulating layer3substantially fills the space between the inner electrical conductor2and the outer electrical conductor4.

The coaxial cable1is further shown to comprise an outer sheath5of an electrically insulating material, which surrounds the outer electrical conductor4. The outer sheath5forms an outer surface of the coaxial cable1, insulating the coaxial cable1from the external environment.

The inner electrical conductor2is preferably made from copper, or an alloy thereof such as CuNi. Additionally, the inner conductor is electrical2preferably silver plated. The electrically insulating layer3, located between the inner electrical conductor2and the outer electrical conductor4, is preferentially made from a polymer such as polytetrafluoroethylene (PFPE). The outer electrical conductor4, like the inner electrical conductor2, is preferably made from copper, or an alloy thereof such as CuNi. Alternatively, the outer electrical conductor4may be manufactured from a stainless steel.

The dimensions of the cable, such as the thickness TINS of the electrical insulating layer3and the thickness Toc of the outer electrical conductor4, and the materials used are selected to give a precise, constant conductor spacing so that the coaxial cable1can function efficiently as a transmission line.

As shown inFIG.1, the coaxial cable1further comprises an opening9, extending from the outer sheath5through the outer electrical and conductor4the electrically insulating layer3towards the inner electrical conductor2. Preferably, the opening9extends radially outwards from the inner electrical conductor2, substantially perpendicular to the longitudinal direction L.

The coaxial cable1further comprises a heat transfer element6, wherein the opening9is configured such that the heat transfer element6fits within the opening9. The heat transfer element6further comprises a first end10and an opposing second end11. The heat transfer element6is positioned within the opening9, wherein the first end10is shown oriented away from the inner electrical conductor2. The first end10is further shown to contact the outer electrical conductor4, at a position approximately in the middle of the outer electrical conductor4. The second end11is shown oriented towards the inner electrical conductor2. The heat transfer element6is made from an electrically insulating material with a high thermal conductivity, preferably having a thermal conductivity much higher than the thermal conductivity of the electrically insulating layer3, preferably having a thermal conductivity more than ten times higher than the thermal conductivity of the electrically insulating layer3, at the working temperature of the electrical interconnect1. The heat transfer element6is configured to form a thermally conductive bridge between the inner electrical conductor2and the outer electrical conductor4, passing through the electrically insulating layer3. The heat transfer element6is preferably fabricated from an aluminum oxide based material such as a sapphire material. Most preferably the sapphire material is a single crystal wherein an axis with the higher thermal conductivity is oriented along the perpendicular direction.

As schematically shown inFIG.1, the heat transfer element6extends in first distance D perpendicular to the longitudinal direction L, extending radially outwards from the inner electrical conductor2. A center line CL1of the heat transfer element6is oriented substantially perpendicular to the longitudinal direction L. The first distance D is approximately equal to the thickness TINSof the insulating layer3.

The coaxial cable1further comprises a first thermal interface material7located between the heat transfer element6and the inner electrical conductor2. The second end11of the heat transfer element6is contacting the first thermal interface material The coaxial cable1further a comprises second thermal interface material8substantially similar or equal to the first thermal interface material7. The second thermal interface material8is contacting the first end10of the heat transfer element6, wherein the second thermal interface material8is located between the heat transfer element6and the outer electrical conductor4. In the example presented inFIG.1, a volume of the second thermal interface material10has been added so that an outermost surface12of the second thermal interface material10is substantially flush with an outermost surface of the coaxial cable1. The first and second thermal interface material10,11are preferably a thermally conductive adhesive such as a silver-filled epoxy.

FIG.2Aschematically shows an example of a cooling system comprising the electrical interconnect1ofFIG.1and a heat sink40of a cryocooler. As schematically shown, the heat sink40is arranged to abut the outer surface12of the second thermal interface material8. Accordingly, the outer surface12of the second thermal interface provides a heat transfer surface, and both the inner electrical conductor2and the outer electrical conductor4can be cooled by the heat sink40which is arranged in thermal contact with said heat transfer surface, due to the thermal bridging mediated by the heat transfer element6.

FIG.2Bschematically shows an alternative example of a cooling system comprising the electrical interconnect1ofFIG.1and a heat sink40of a cryocooler. In this example, the heat sink40or cooling medium is provided in contact with the outer electrical conductor4at a position along the electrical interconnect1where the outer sheath5has been removed to provide a heat transfer surface13. Preferably, and as schematically shown inFIG.2B, this removal of the outer sheath5is arranged at or near the location of the heat transfer element6. Accordingly, the heat sink40directly cools the electrical4. outer conductor Due to the thermal conductivity of the outer electrical conductor4and the thermal bridging between the inner electrical conductor2and the outer electrical conductor4, as mediated by the heat transfer element6, the inner electrical conductor2is also cooled by the heat sink40.

FIG.3illustrates a second example of an electrical interconnect20according to the invention. In this example, the electrical interconnect20is in the form of a coaxial connector20. TheFIG.3shows a schematic cross-section of coaxial connector20comprising an inner electrical conductor21that extends along a center line C12of the coaxial connector20. The coaxial connector20further comprises an electrically insulating layer22, wherein the electrically insulating layer22is concentric with, and substantially surrounds the inner electrical conductor21. The electrically insulating layer22has a thickness TINS.

The coaxial connector20further comprises an outer electrical conductor23, wherein the outer electrical conductor23is concentric with both the inner electrical conductor21and the electrically insulating layer22, wherein the outer electrical conductor23is shown surrounding the electrically insulating layer22.

The coaxial connector20ofFIG.3further comprises an opening27, extending from the outer electrical conductor23, through the electrically insulating layer22towards the inner electrical conductor21. The opening27in this example is a substantially circle-cylindrical opening which extends radially outwards from the inner electrical conductor21.

The coaxial connector20further comprises a heat transfer element24with a circle-cylindrical shape, wherein the opening27is configured such that the heat transfer element24fits within the opening27. The heat transfer element24further comprises a first end25and an opposing second end26. The heat transfer element24is positioned within the opening27, wherein the first end25is shown oriented away from the inner electrical conductor21. The outer electrical conductor23is arranged to abut the circumference of the first end25of the heat transfer element24in order to provide a thermal contact between the outer electrical conductor23and the heat transfer element24. The surface of the heat transfer element24at the first end25is arranged substantially flush with the outer surface of outer electrical conductor23. The second end26is oriented towards and abutting the inner electrical conductor21, wherein the second end26provides a thermal contact between the inner electrical conductor21and the heat transfer element24.

The heat transfer element24is prepared from an electrically insulating material with a high thermal conductivity, preferably with a thermal conductivity which is at least ten times higher than the thermal conductivity of the electrically insulating layer22, at the working temperature of the coaxial connector20. The heat transfer element24is configured to form a thermally conductive bridge between the inner electrical conductor21and the outer electrical conductor23, passing through the electrically insulating layer22.

A center line CL3of the cylindrically shaped heat transfer element24is shown oriented perpendicular to a center line CL2of the coaxial connector20. The heat transfer element24is shown extending a first distance D along the center line CL3, extending radially outwards from the inner electrical conductor21. The first distance D is shown in theFIG.3to be approximately equal to a sum of the thickness TINSof the insulating layer22and the thickness TOCof the outer electrical conductor23at the position of the opening27.

As schematically shown inFIG.3, in the direction of the center line CL2of the connector20, the coaxial connector20comprises a male connector end28and an opposing female connector end29. The male connector end28is configured for connecting with a female connector end of another electrical interconnect, while the female connector end29is configured for connecting with a male connector end of another electrical interconnect.

The male connector end28comprises a first cavity31configured to fit around an outer electrical conductor of another electrical interconnect. The male connector end28further comprises a pin27, disposed within the first cavity31, wherein the pin27is formed by the inner electrical conductor21extending along the center line CL2of the coaxial connector20.

The female connector end29is shown to comprise a second cavity33configured for accepting an insulating layer of another electrical interconnect. The female connector further comprises a third cavity32configured for accepting and making electrical contact with an inner electrical conductor of another electrical interconnect.

The coaxial connector20is configured such that the inner electrical conductor21can be cooled, via the heat transfer element24, by providing a heat sink or a cooling medium to the outer electrical conductor23and/or the first end25of the heat transfer element24of the coaxial connector20. In order to enhance the transfer of heat from the inner electrical conductor, a thin layer of a thermal interface material may be provided between the second end26of the heat transfer element24and the inner electrical conductor21, and/or a thin layer of a thermal interface material may be provided between the circumference of the first end25of the heat transfer element24and the outer electrical conductor23.

Preferably, the heat transfer element24comprises a Sapphire, Diamond or Silicon material which are substantially electrically insulating material with a relatively high thermal conductivity. The heat transfer element24thus provides a bridge between the inner electrical conductor21and the outer electrical conductor23. Preferably, the second end26of the heat transfer element24is glued against the inner electrical conductor26, using a silver filled epoxy, and the outer circumference of the first end25of the heat transfer element24is glued against the inner circumference of the opening in the outer electrical conductor23, in order to enhance the thermal conduction between the inner electrical conductor24and the outer electrical conductor23via the heat transfer element24.

In the example shown inFIG.3, both the inner electrical conductor21and the outer electrical conductor23can be cooled by providing a heat sink40or a cooling medium such as liquid helium, in contact with the outer surface of the outer electrical conductor23, which provides a heat transfer surface34.

When cooling the coaxial connector20down to cryogenic temperatures using the heat sink40, and measuring the temperature of the inner conductor via a small thermometer glued to the inner conductor, revealed that the inner conductor could be cooled to about 120 mK with a standard connector without the heat transfer element24and to approximately 15 mK with a Sapphire heat transfer element according to the present invention.

In addition, since the heat transfer element24is an electrical insulator and has relatively small dimensions, no effect on the RF propagation has been detected.

While the coaxial connector as shown inFIG.3is formed as a SMA-type connector, it is noted that the coaxial connector alternatively may be formed as for example a SMP, MCX or MMCX-type coaxial connector.

FIG.4schematically shows longitudinal cross-section of a third example of an electrical interconnect40comprising two or more heat transfer elements46a,46b, which are arranged spaced apart over a distance41in a longitudinal direction of the electrical interconnect40. The electrical interconnect40is configured to provide a coaxial cable comprising an inner electrical conductor42, an electrically insulating layer43that surrounds the inner conductor42, an outer electrical conductor44that surrounds the electrically insulating layer43and is arranged coaxial with the inner electrical conductor42. For this example, the same materials may be used as described above with reference to the example ofFIG.1, but other suitable materials are also possible. As schematically shown inFIG.4, the electrical interconnect40comprises at least two heat transfer elements46a,46b, each of which is glued to the inner electrical conductor42using heat conducting glue47(for example silver filled epoxy glue) and to the outer electrical conductor44using heat conducting glue48(for example silver filled epoxy glue). By arranging two or more heat transfer elements46a,46bin parallel along the longitudinal axis of the electrical interconnect40, also longer electrical interconnecting cables can be effectively cooled.

FIG.5schematically shows transverse cross-section of a fourth example of an electrical interconnect50comprising two heat transfer elements56a,56b, which are arranged in a transverse plane substantially perpendicular to a longitudinal direction of the electrical interconnect50. The electrical interconnect50is configured to provide a coaxial cable comprising an inner electrical conductor52, an electrically insulating layer53that surrounds the inner conductor52, an outer electrical conductor54that surrounds the electrically insulating layer53and is arranged coaxial with the inner electrical conductor52. For this example, the same materials may be used as described above with reference to the example ofFIG.1, but other suitable materials are also possible. As schematically shown inFIG.5, the electrical interconnect50comprises two heat transfer elements56a,56b, each of which is glued to the inner electrical conductor52using heat conducting glue67(for example silver filled epoxy glue) and to the outer electrical conductor54using heat conducting glue58(for example silver filled epoxy glue). By arranging two heat transfer elements56a,56bin parallel along the circumference of the electrical interconnect50, the heat transfer between the inner electrical conductor52and the outer electrical conductor54can be enhanced.

It is noted that in a further example, the electrical interconnect of the present invention comprises two or more heat transfer elements, which are arranged spaced apart in a direction along a longitudinal axis of the electrical interconnect and two or more heat transfer elements which are arranged in a transverse plane substantially perpendicular to a longitudinal direction of the electrical interconnect, thus providing a combination of the third and fourth example shown inFIGS.4and5and described above.