Patent Application
20230238178
This disclosure relates generally to magnets and magnetic compositions and structures, and more particularly to Rare Earth-Barium-Copper Oxide (REBCO) magnets, and methods of making the same.
No insulation (NI) REBCO pancake magnet coils, characterized by the elimination of typical turn-to-turn insulation, have several advantages over conventional insulated coils. For example, due to low turn-to-turn electrical resistance, when magnet quench happens in a NI REBCO coil, the quench current automatically bypasses the normal zone, and a hot spot is avoided. This self-quench-protection ability eliminates the need for a quench detection and protection system that can be very challenging and costly in a large high field REBCO magnet. Consequently, an NI REBCO coil is very stable, which allows for a thinner copper stabilizer on the REBCO conductor. With the thinner stabilizer and the elimination of turn-to-turn insulation, the NI REBCO provides a very high engineering current density and high mechanical strength. These suggest that this technology enables very compact magnets to reach a very high magnetic field.
There are, however, drawbacks in the current state of the NI REBCO coil technology. For example, high turn-to-turn contact resistance (Rct) compromises the REBCO coil's self-quench-protection ability, risking magnet burn-out during a quench. On the other hand, low turn-to-turn contact resistance results in a REBCO coil magnet having a long charging and discharging delay with high energy losses during a field ramp. Low turn-to-turn contact resistance is further characterized by high transient electrical currents during magnet quench which results in high electromagnetic stressed that could damage the magnet.
Accordingly, improved coils for superconducting magnets and methods of controlling turn-to-turn contact resistance are needed.
In one aspect, improved methods for making superconducting magnets are provided. In one embodiment, a method includes providing a rare earth barium copper oxide (REBCO) superconducting tape; dipping the REBCO tape in a tin-lead solder bath to form a layer of tin-lead solder on a surface of the REBCO tape; oxidizing a stainless steel tape; and co-winding the dipped REBCO tape and the oxidized stainless steel tape into a coil.
In another aspect, improved coils for superconducting magnets are provided. In one embodiment, a coil for a superconducting magnet includes a REBCO superconducting tape; a layer of tin-lead solder coated on a surface of the REBCO superconducting tape; and a stainless steel tape, wherein the stainless steel tape has been oxidized, wherein the coated REBCO superconducting tape and oxidized stainless steel tape have been co-wound to form the coil.
The detailed description is set forth with reference to the accompanying drawings. The use of the same reference numerals may indicate similar to identical items. Various embodiments may utilize elements and/or components other than those illustrated in the drawings, and some elements and/or components may not be present in various embodiments. Elements and/or components in the figures are not necessarily drawn to scale. Throughout this disclosure, depending on the context, singular and plural terminology may be used interchangeably.
New and improved REBCO superconducting tapes and coils for superconducting magnets, and methods for their manufacture have been developed. In particular, the long magnet charging time, high field-ramp-losses, and high transient electrical currents during magnet quench characteristic of NI REBCO magnets having low contact resistance (Rct) may be mitigated by controlling Rct. Additionally, deteriorating self-quench-protection ability characteristic of NI REBCO magnets having high Rct may be similarly mitigated by controlling Rct. In various embodiments described herein, greater control over Rct may be accomplished with a layer of tin-lead solder coated on a surface of a REBCO superconducting tape. A stainless steel tape may be used as mechanical reinforcement of the REBCO superconducting tape, which may be oxidized. In addition, without intending to be bound by any particular theory, it is believed that the coil with graded Rct is used to reduce the ramp loss, as well as to improve stability and recovery speed after a quench in large NI REBCO magnets.
As used herein, “no insulation” or “NI” REBCO coils refer to REBCO coils that omit turn-to-turn insulation. “Turn-to-turn insulation,” in the context of high temperature superconductors, refers to an organic material such as polyimide film inserted between or co-wound with the layers of REBCO coil upon winding into a coil shape. Insulated RECBO coils are characterized by a radial resistance that is essentially infinite due to the inclusion of insulation. NI REBCO coils may have one or more resistive layers disposed on the REBCO superconducting coil, such as that described in U.S. Pat. No. 11,282,624 to Florida State University Research Foundation, Inc., which is incorporated herein by reference in pertinent part. Although these resistive layers interact with the Rct of a REBCO superconducting coil, they do not insulate the REBCO superconducting coil, i.e., the radial resistance is not essentially infinite, so such layers are not necessarily excluded in NI REBCO coils.
In some embodiments, Rct can be optimized to achieve a relatively short charging delay time and low ramp losses without jeopardizing the coil's self-quench-protection ability. Without intending to by any particular theory, it is believed that Rct is a critical parameter in the development of NI coil technology.
As used herein, “substantially coated” is used to mean that all or a majority of at least one surface is coated with a substance, e.g., at least one side of a tape. For example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, or any ranges therebetween, of the surface is coated with the substance.
As used herein, a “tape” is a long, thin, flexible strip of material, e.g., of a metal, as that term is understood in the art related to superconducting magnets.
Throughout this disclosure, various aspects may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
As used herein, the term “about” with reference to dimensions refers to the dimension plus or minus 10%.
Methods of Making Coils for Superconducting Magnets
In some embodiments, a method of making a coil for a superconducting magnet includes providing a REBCO superconducting tape, and dipping the REBCO tape in a tin-lead solder bath to form a layer of tin-lead solder on a surface of the REBCO tape. In some embodiments, the method includes oxidizing a stainless steel tape, and co-winding the dipped REBCO tape and the oxidized stainless steel tape into a coil. In some embodiments, the coil for a superconducting magnet is a no-insulation coil.
In some embodiments, dipping the REBCO tape in a tin-lead solder bath includes a reel-to-reel dip coating.
In some embodiments, the REBCO tape passes through the tin-lead solder bath at a linear speed of from about 1 m/min to about 6 m/min. In some embodiments, the tin-lead solder bath is maintained at a temperature of from about 200° C. to about 260° C. In some embodiments, dipping the REBCO tape in the tin-lead solder bath is performed in a manner so as to minimize thermal degradation of the critical current (Ic) of the REBCO tape. In other words, the REBCO tape may pass though the tin-lead solder having a temperature and at a speed such that thermal degradation of Ic is negligibly small.
One skilled in the art in view of the description herein and the examples below can determine suitable tin-lead solder compositions and conditions to achieve the desired coating composition. In some embodiments, the tin-lead solder is 63/37 Sn—Pb. That is, the tin-lead solder is an alloy comprising 63% tin and 37% lead. In some embodiments, the layer of tin-lead solder has a thickness from about 1 μm to about 5 μm. For example, in various embodiments, the thickness of the layer of tin-lead solder is about 1 μm, about 2 μm, about 3 μm, about 4 μm, about 5 μm, or any ranges therebetween. As depicted in
In some embodiments, oxidizing the stainless steel tape includes heating the stainless steel tape in a furnace, for example, by passing the stainless steel tape through the furnace on a reel-to-reel process.
One skilled in the art in view of the description herein and the examples below can determine suitable tin-lead solder compositions and conditions to achieve the desired degree of oxidation on the stainless steel tape, which depends at least in part on the composition of the clean (i.e., pre-oxidized) stainless steel tape, the temperature of the furnace, and the rate at which the stainless steel tape passes through the furnace. In some embodiments, the stainless steel tape includes 316L stainless steel. In some embodiments, heating the stainless steel tape includes passing the stainless steel tape through the furnace from reel-to-reel at a speed of about 1 m/min. In some embodiments, the furnace has a temperature of from about 400° C. to about 500° C. Without intending to be bound by any particular theory, it is believed that the temperature of the furnace through which the stainless steel tape passes affects the Rct of the resulting coil after the oxidized stainless steel tape is co-wound with the tin-lead solder-coated REBCO tape. Increases in the furnace temperature result in increases in the Rct of the coil. Thus, by controlling the temperature of the furnace during oxidation of the stainless steel tape, the Rct of the resulting coil may be controlled.
In some embodiments, the method is effective to produce a coil having a turn-to-turn contact resistance (Rct) of from about 1 mΩ-cm2 to about 11 mΩ-cm2. For example, the method may be effective to produce a coil having an Rct of about 10 mΩ-cm2 at 600° C. In some embodiments, the method is effective to produce a coil having an Rct of about 4 mΩ-cm2 at 500° C.
In some embodiments, the method is effective to produce a coil having an Rct that reduces by less than 75% after 30,000 pressure cycles. It has been unexpectedly discovered that oxidation of the stainless steel tape prior to co-winding the oxidized stainless steel tape with the tin-lead solder-coated REBCO tape significantly mitigates deterioration in Rct as a result of pressure cycling.
Coils for Superconducting Magnets
Coils for superconducting magnets are also disclosed herein. An example of a magnet 400 including coils 402 is shown in
In some embodiments, the coil includes a REBCO superconducting tape with a layer of tin-lead solder coated on a surface of the REBCO superconducting tape. In some embodiments, the coil includes a stainless steel tape that has been oxidized. In some embodiments, the tin-lead solder-coated REBCO superconducting tape is co-wound with the oxidized stainless steel tape to form the coil. In some embodiments, the coil is a no-insulation (NI) coil that omits any turn-to-turn insulation.
In some embodiments, the layer of tin-lead solder includes 63/37 Sn—Pb having a thickness of from about 1 μm to about 5 μm. In some embodiments, the stainless steel tape includes 316L stainless steel.
In some embodiments, the coil has an Rct of from about 1 mΩ-cm2 to about 11 mΩ-cm2. For example, the coil may have an Rct of about 10 mΩ-cm2 at 600° C. In some embodiments, the coil has an Rct of about 4 mΩ-cm2 at 500° C.
In some embodiments, the coil has a turn-to-turn contact resistance (Rct) that reduces by less than 75% after 30,000 pressure cycles. It has been unexpectedly discovered that a stainless steel tape that has been oxidized co-wound with the tin-lead solder-coated REBCO tape significantly mitigates deterioration in Rct as a result of pressure cycling. Absent oxidation on the stainless steel tape and the layer of tin-lead solder on the REBCO superconducting tape, a co-wound coil experiences a drop in Rct of over 99% after 30,000 pressure cycles from 2.5 MPa to 25 MPa and back, as shown in
The invention may be further understood with reference to the following non-limiting examples.
Coils were formed as described herein and the temperature of the furnace in which the stainless steel tape is oxidized was varied to measure the effect on the Rct of the coil. In this test, the furnace was a horizontal furnace into which the stainless steel tape is inserted, allowed to rest for 1 minute during heat treatment, and then removed. Tests were run with furnace set points of 300° C., 325° C., 350° C., 375° C., and 400° C. The results are displayed in
Coils were formed as described herein and the temperature of the furnace through which the stainless steel tape is passed was varied to measure the effect on the Rct of the coil. In this test, the furnace was a vertical furnace through which the stainless steel tape was passed on a reel-to-reel system. Tests were run with furnace set points of 350° C., 375° C., 400° C., 425° C., 450° C., and 475° C. The results are displayed in
Three coils were produced as described herein. Two coils were cycled between 2.5 MPa and 25 MPa at 600° C., and a third coil was cycled between 2.5 MPa and 25 MPa at 500° C. All three coils were cycled between 2.5 MPa and 25 MPa 30,000 times while measuring the turn-to-turn contact resistance (Rct). The results of the test are presented in
As shown in Table A and
While the disclosure has been described with reference to a number of embodiments, it will be understood by those skilled in the art that the disclosure is not limited to such embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not described herein, but which are commensurate with the spirt and scope of the disclosure. Conditional language used herein, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, generally is intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements or functional capabilities. Additionally, while various embodiments of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure it not to be seen as limited by the foregoing described, but is only limited by the scope of the appended claims.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/267,023, filed Jan. 21, 2022, which is incorporated by reference herein in its entirety.
This invention was made with government support under grant number DMR-1644779 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63267023 | Jan 2022 | US |
