Superconducting cavity coupler

A cavity coupler comprising of an outer coupler body, at least one shield formed inside the outer coupler body wherein the relationship between the shield and the outer coupler body form at least one chamber, an antenna configured to provide a radio frequency signal, and a flange for connecting the cavity coupler to a superconducting cavity. In an embodiment, the outer coupler body is formed of stainless steel. In an embodiment, the at least one shield is formed of copper.

TECHNICAL FIELD

Embodiments are generally related to the field of superconducting cavities. Embodiments are further related to a main coupler for radiofrequency (RF) superconducting cavities.

BACKGROUND

A superconducting cavity coupler's function is to deliver RF power from the outside RF power source with minimal resistive losses to the superconducting cavity. At the same time, the coupler isolates the cavity vacuum from the outside environment and minimizes heat flow from the surroundings to the cryogenic temperature cavity. To prevent heat flow, the outer conductor of a coupler is made of stainless steel because of its low thermal conductivity. To decrease ohmic losses, the stainless steel is coated with a thin layer of copper. This coating is generally applied to the stainless steel using a galvanic or plasma-based process.

This approach has several drawbacks. First, the technology used to plate copper is not sufficiently developed to provide a reliable reproducible coating. For example, the copper coating often flakes or peels away from the stainless steel. Copper flaking is fatal for the superconducting cavity. In addition, the copper layer increases the thermal conductivity of the stainless steel outer conductor and increases the heat flow to the cavity. As a result, the cavity requires a more powerful cryo-plant to compensate, which reduces the efficiency of the system. Finally, the copper layer has a low residual-resistance ratio (RRR). It increases ohmic losses, deposits additional heat into the superconducting cavity, and reduces system efficiency.

An additional difficulty arises in protecting the ceramic surface of the dielectric RF window from charged particles emanating from the superconducting cavity. In the prior art, some waveguide couplers use a bent waveguide to remove the dielectric surface from line of sight of the superconducting cavity. This provides the dielectric surface with some protection from charged particles. However, this approach is not useable in a coaxial coupler.

Accordingly, methods and systems are required for superconducting cavity couplers that avoid these disadvantages.

SUMMARY

It is, therefore, one aspect of the disclosed embodiments to provide a method and system for superconducting cavities.

It is another aspect of the disclosed embodiments to provide a method and system for superconducting cavity couplers.

It is another aspect of the disclosed embodiments to provide methods, systems, and apparatuses for main couplers for superconducting radiofrequency cavities.

The aforementioned aspects and other objectives and advantages can now be achieved as described herein. Systems and methods for a cavity coupler comprise an outer coupler body, at least one shield formed inside the outer coupler body wherein the relationship between the shield and the outer coupler body form at least one chamber, an antenna configured to provide a radio frequency signal, and a flange for connecting the cavity coupler to a superconducting cavity. In an embodiment, the outer coupler body is formed of stainless steel. In an embodiment, the at least one shield is formed of copper.

The at least one shield may comprise three or more shields. The three shields further comprise a first shield connected to a first end of the outer body, a second shield connected to a thermal intercept, wherein a first end of the second shield overlaps a second end of the first shield, and a third shield connected to a second end of the outer body, wherein a first end of the third shield overlaps a second end of the second shield.

In an embodiment, the cavity coupler further comprises a first disk and a second disk, wherein the first disk and the second disk overlap in order to prevent a line of sight through the cavity coupler to an RF window.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary embodiment of a superconducting cavity coupler100. Superconducting cavity coupler provides a coupling between a superconducting cavity and an external radio frequency source. Superconducting cavity coupler100is coupled to a superconducting cavity with a flange170. The cavity coupler100uses at least one, and potentially many shields to facilitate the transmission of RF power from an outside power source to a superconducting cavity efficiently. In certain embodiments, the super conducting cavity coupler may comprise a coaxial cavity coupler.

In a preferred embodiment one or more shields, such as shield110, shield115, and shield125, are formed on the inside of the cavity coupler. The shields are formed of a material that has good electrical conductivity, such as copper. In other embodiments, the shields may be composed of any highly conductive material. The copper shields are preferably formed of solid copper. Solid copper shields do not flake and therefore eliminate the danger of fouling the superconducting cavity associated with prior art approaches.

The shields in the superconducting cavity coupler100create two chambers, chamber135and chamber140, separated by thermal intercept145. The chambers135and140are defined by the shielding created by the shields and therefore have very low electromagnetic fields. As a result, losses, even in the uncoated stainless steel body, are negligible. The majority of the RF current flows on copper shields. Since the copper shields are made of solid copper, the RRR is very high and ohmic losses are smaller than prior art methods using copper plated on the interior walls of the cavity.

In an embodiment, a slot105is formed between shield110and shield115and another slot120between shield115and shield125. Slot105and slot120prevent heat flow through the copper shield110, copper shield115, and shield125. All of the heat flow travels through the outer conductor130. Outer conductor130is formed from a low thermal conductivity material such as stainless steel tube. Other low thermal conductivity materials may alternatively be used. The outer conductor130provides better thermal isolation of superconducting cavity coupler100from the surrounding room temperature environment.

Shield110is configured to at least partially overlap shield115, and shield115is similarly configured to at least partially overlap shield125. In the embodiment shown, shield110, shield115, and shield125have a substantially cylindrical configuration. In the embodiment shown, shield110and shield125connect to first and second ends, respectively, of the outer conductor130, while shield115attaches midway between the first and second ends of the outer conductor130to thermal intercept145. The connection between the shields and the outer conductor can be achieved via welding, brazing, screws, bolts, rivets, or other such connecting means provided the connection provides sturdy mechanical contact and good electrical contact.

The spatial configuration of the shields is critical. The configuration of the shields significantly reduces the electromagnetic fields at the surface of the outer conductor130. However, the shields do not increase the thermal conductivity of the outer conductor. In an embodiment, the shields do not have thermal or mechanical contact between each other. As a result, superconducting cavity coupler100takes advantage of the thermal conductivity of the outer conductor for thermal isolation and the electrical conductivity of the shield material to entrain the RF current flow. This allows superconducting cavity coupler100to have a low thermal conductivity and simultaneously high electrical conductivity.

At one end of the chamber a dielectric RF window165, commonly comprising a ceramic material, is formed which separates the vacuum drawn on the coupler side of the RF window165and the external atmosphere on the right side of the RF window165. The RF window165must remain transparent to electromagnetic waves while preserving the desired vacuum. The possible flow of charged particles from the superconducting cavity to the ceramic window may damage the RF window165.

The superconducting cavity coupler100can therefore include disk150and disk155. Disk150and disk155surround the RF antenna160. Disk150can be formed on and/or substantially around antenna160. Disk155can be formed on shield115. The disks may be formed to be substantially flat and circular. However, the disks may be formed in other shapes provided that disk155at least partially overlaps disk150. The overlapping of disk150and disk155eliminates line of sight between the output coupler and the ceramic surface of the dielectric RF window165. Disk150and disk155effectively hide the dielectric surface of the dielectric RF window165from charged particles that can come from the superconducting cavity. In an embodiment, disk155can be kept at a low temperature (e.g., approximately that of liquid nitrogen). This significantly decreases thermal radiation propagating from the room temperature dielectric RF window165towards the superconducting cavity.

Disk150and disk155collect charged particles (e.g., electrons) without accumulating a charge. Accordingly, the disks must be made of metal. Moreover, to reduce ohmic losses and improve the parameters of the superconducting cavity coupler100, the metal should have good electrical conductivity. In one embodiment, disk150and disk155can be formed of copper.

It should be appreciated that in certain embodiments of superconducting cavity coupler100both the shields and the disks may be present, while other embodiments may use only the disks or only the shields.

FIG. 2illustrates a flow chart associated with a method200for coupling a cavity to a radio frequency source according to the disclosed embodiments. The method begins at step205. A step210, an outer coupler body can be shielded with at least one internal shield. The relationship between the shields and the coupler body can form chambers at step215. The cavity coupler can be connected to a superconducting cavity with a flange as illustrated at step220. At step225, a radio frequency signal can be transmitted to the superconducting cavity with an antenna running though the body of the coupler cavity. The method then ends at step230.

Based on the foregoing, it can be appreciated that a number of embodiments, preferred and alternative, are disclosed herein. For example, in one embodiment, a cavity coupler comprises an outer coupler body, at least one shield formed inside the outer coupler body wherein the relationship between the shield and the outer coupler body form at least one chamber, an antenna configured to provide a radio frequency signal, and a flange for connecting the cavity coupler to a superconducting cavity.

In an embodiment, the outer couple body is formed of stainless steel. In an, embodiment, the at least one shield is formed of copper.

In another embodiment, the at least one shield comprises three shields. The three shields further comprise a first shield connected to a first end of the outer body, a second shield connected to a thermal intercept, wherein a first end of the second shield overlaps a second end of the first shield, and a third shield connected to a second end of the outer body, wherein a first end of the third shield overlaps a second end of the second shield.

In another embodiment, the cavity coupler further comprises a first disk and a second disk, wherein the first disk and the second disk overlap in order to prevent a line of sight through the cavity coupler to an RF window.

In an embodiment, the cavity coupler comprises a coaxial cavity coupler.

In another embodiment, a system for coupling a cavity to a source comprises an outer coupler body, at least one shield formed inside the outer coupler body wherein the relationship between the shield and the outer coupler body form at least one chamber, an antenna configured to provide a radio frequency signal, and a flange for connecting the cavity coupler to a superconducting cavity.

In an embodiment of the system, the outer coupler body is formed of stainless steel. In an embodiment of the system, the at least one shield is formed of copper.

In an embodiment of the system, the at least one shield comprises three shields. The three shields further comprise a first shield connected to a first end of the outer body, a second shield connected to a thermal intercept, wherein a first end of the second shield overlaps a second end of the first shield, and a third shield connected to a second end of the outer body, wherein a first end of the third shield overlaps a second end of the second shield.

In an embodiment, the system further comprises a first disk and a second disk, wherein the first disk and the second disk overlap in order to prevent a line of sight through the cavity coupler to an RF window.

In an embodiment of the system, the cavity coupler comprises a coaxial cavity coupler.

In yet another embodiment, a method for coupling a cavity to a source comprises shielding an outer coupler body with at least one shield, forming at least one chamber with a relationship between the shield and the outer coupler body, connecting the cavity coupler to a superconducting cavity with a flange, and providing a radio frequency signal to a cavity with an antenna within the coupler body.

In an embodiment, the method further comprises forming the outer coupler body of stainless steel. In an embodiment, the method further comprises forming the at least one shield of copper.

In an embodiment, the at least one shield comprises three shields.

In an embodiment, the method further comprises connecting a first shield to a first end of the outer body, connecting a second shield to a thermal intercept, wherein a first end of the second shield overlaps a second end of the first shield, and connecting a third shield to a second end of the outer body, wherein a first end of the third shield overlaps a second end of the second shield.

In an embodiment, the method further comprises overlapping a first disk and a second disk, in order to prevent a line of sight through the cavity coupler to an RF window.