Patent Application
20120007703
1. Technical Field
Embodiments of the invention relate to current lead assemblies for superconducting magnets, and more specifically to a current lead assembly having a cooling system for cooling one end of the current lead that is electrically coupled to the superconducting magnet.
2. Discussion of Related Art
Superconducting magnets conduct electricity with effectively zero resistance as long as the magnets are maintained at a suitably low temperature, which is referred to as “superconducting temperature” hereinafter. Accordingly, cryogenic systems are used to ensure that the superconducting magnets work at the superconducting temperature.
Superconducting magnets generally comprise superconducting coils electrically coupled to a power supply through current leads for transmitting the electrical current to the superconducting coils. These current leads each comprise one end electrically coupled to the superconducting coil, and another end electrically coupled to the power supply. It has been realized that Joule heat (or ohmic heat) generated from the current leads may inevitably propagate to the superconducting coils. Accordingly, a cooling apparatus is used for cooling the end of the current leads electrically coupled to the superconducting coils (hereinafter referred to as a “cold end”). The other end that is electrically coupled to the power supply (hereinafter referred to as a “warm end”).
One type of cooling apparatus used for the current leads comprises a heat station which is in thermal contact with, but is electrically isolated from, the cold end of the current lead. The heat station usually comprises metal materials, such as pure copper or aluminum for example, with good thermal conductivities to form a thermal conduction path from the current lead to a cryocooler. The thermal conduction path is electrically separated by isolative elements such as one or more ceramic pads. These ceramic pads provide electric isolation and are soldered to the heat station to minimize the thermal resistance. However, the thermal resistance of the ceramic pads becomes higher as the temperature of the thermal conduction path decreases. Moreover, the bonding of the ceramic pads and the heat station is usually accomplished by soldering. This becomes unreliable as the bond may break due to mechanical and thermal stresses.
It may be desirable to have a current lead assembly with a cooling system that differs from those assemblies that are currently available for both effectively cooling the cold ends of the current leads, as well as electrically insulating the cooling system from the current leads.
In accordance with one embodiment, a current lead assembly is provided. A current lead assembly includes a current lead having an end, at least one heat station thermally coupled to the end, a cryogen-flow path extending through the heat station and comprising at least one connection, and a cryogen generation source fluidly coupled to the cryogen-flow path through the connection.
In accordance with another embodiment, a superconducting magnet system includes at least one superconducting coil comprising a positive and a negative superconducting magnet terminal, a positive and a negative current leads each having an end electrically coupled to a corresponding one of the positive and negative superconducting magnet terminals, and a cooling system. The cooling system includes at least one heat station physically and thermally coupled to the ends of the positive and negative current leads, and a cryogen-flow path extending through the heat station.
In accordance with still another embodiment, a cooling method includes physically and thermally coupling a heat station to an end of a conductive current lead, coupling at least one connection tube to a through hole in the heat station to form a cryogen-flow path in the through hole and the connection tube, and flowing a liquid cryogen into the through hole through the connection tube.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Embodiments of the invention relate to a current lead assembly for a superconducting magnet. The current lead assembly comprises at least one positive current lead, at least one negative current lead, and a cooling system. Each of the positive and negative current leads has one end (“warm end”) electrically coupled to a power supply, and another end (“cold end”) electrically coupled to the superconducting magnet. The cooling system comprises a heat station in thermal contact with the cold ends of the current leads, and a cryogen-flow path extending through the heat station. A fluid cryogen flows in the cryogen-flow path, and removes heat from the cold end by converting the fluid cryogen into gas. Accordingly, the cold ends of the current leads are maintained at a low temperature and do not transmit heat to the superconducting magnet. The electric current is transmitted from the current leads to the positive and negative terminals of the superconducting coil at the cold end. The heat station maintains the cold end of the current leads at the superconducting temperature to ensure the superconducting operation of the coil terminals.
Referring to
Referring to
In the illustrated embodiment, the cooling system 28 comprises at least one heat station 30a, 30b thermally coupled to the cold ends 24 of the positive and negative current leads 16, 18, and at least one cryogen-flow path 32a, 32b extending through the heat stations 30a, 30b, respectively. A fluid cryogen flows in the cryogen-flow path, and removes heat from the cold ends 24 by converting the fluid cryogen into a gas. Accordingly, the cold ends 24 of the positive and negative current leads 16, 18 are maintained at a low temperature and do not transmit heat to the magnet 12. In certain embodiments, the liquid cryogen that flows in the at least one cryogen-flow path 32a, 32b comprises nitrogen, neon, hydrogen, helium, or any other suitable cryogen capable of withdrawing sufficient heat from the cold ends 24.
In the illustrated embodiment of
In the illustrated embodiment of
In certain embodiments, the first and second cryogen-flow paths 32a, 32b each comprise at least one connection for introducing a liquid cryogen into the path. In the illustrated embodiment of
In the illustrated embodiment, the cooling system 28 comprises cryogen generation sources 42a, 42b respectively fluidly coupled to the first and second connections 38a, 38b, 40a, 40b of the first and second cryogen-flow paths 32a, 32b. In one embodiment, the cryogen generation sources comprise cryogen containers 42a, 42b storing liquid cryogen. The liquid cryogen flows from the cryogen containers 42a, 42b into the cryogen-flow paths 32a, 32b from the first connections 38a, 38b, and gases exit the first and second cryogen flow paths 32a, 32b from the second connections 40a, 40b. In the illustrated embodiment, the cryogen containers 42a, 42b are positioned above the first and second cryogen-flow paths 32a, 32b. Accordingly, the liquid cryogen flows form the cryogen containers 42a, 42b driven by gravity.
In the illustrated embodiment, the first and second cryogen-flow paths 32a, 32b receive liquid cryogen from different cryogen containers. In the illustrated embodiment, the first and second connections 38a, 38b, 40a, 40b of the first and second cryogen-flow paths 32a, 32b are fluidly coupled to the cryogen containers 42a, 42b. In other embodiments, only the first connections 38a, 38b may be fluidly coupled to the cryogen container 42a, 42b for receiving the liquid cryogen, and the second connections 40a, 40b may be coupled to another container to store the gas output from the first and second cryogen-flow paths 32a, 32b, or to a re-condenser for re-condensing the gas back into a liquid cryogen, or to vent out.
Referring to
Referring to
At a start-up operation of the cooling system, a certain amount of cryogen is introduced to the cryogen-flow path 52 from an inlet (not shown) which is later closed when adequate cryogen has been introduced in the cryogen flow path 52. In one embodiment, the cryogen introduced into the cryogen-flow path 52 is a liquid cryogen. In other embodiments, the cryogen introduced into the cryogen-flow path 52 is a gas and is continuously converted into the liquid cryogen by the cryogen generation source 54. During the normal cooling operation of the cooling system 50, the liquid cryogen flows in the cryogen-flow path 52. In certain embodiments, the through holes 34 in the first and second heat stations 30a, 30b are filled with liquid cryogen during the normal cooling operation of the cooling system 50 for maintaining the cold ends 24 of the current leads at the low temperature. Part of the liquid cryogen in the cryogen-flow path 32 is boiled-off as a gas to absorb heat from the cold ends 24 of the current leads 16, 18. The boiled-off gas flows to the cryogen generation source 54 and is converted into liquid cryogen which flows back into the cryogen-flow path 52. Accordingly, the conversion of the liquid cryogen and gas is automatically performed within the cooling system.
The embodiments described herein are examples of compositions, structures, systems, and methods having elements corresponding to the elements of the invention recited in the claims. This written description may enable those of ordinary skill in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the invention recited in the claims. The scope of the invention thus includes compositions, structures, systems and methods that do not differ from the literal language of the claims, and further includes other structures, systems and methods with insubstantial differences from the literal language of the claims. While only certain features and embodiments have been illustrated and described herein, many modifications and changes may occur to one of ordinary skill in the relevant art. The appended claims cover all such modifications and changes.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010100021 | Jan 2010 | CN | national |
