Record High Magnetic Field (45.5 Tesla) Achieved Using High Temperature Superconducting Ceramic.
The paper I'll discuss in this post is this: 45.5-tesla direct-current magnetic field generated with a high-temperature superconducting magnet (David C. Larbalestier et al Nature, Published On Line 6/12/2019).
Recently I met with an old friend and his wife for dinner, who I hadn't seen for a long time, and we got around, of course, as old friends do when they get old, to talking about our kids, and when I discussed what my kid is doing over the summer we got on the subject of neutrons. I think about all the time about neutrons, albeit in a very different way than my son thinks about them, since my son is concerned with their De Broglie wavelengths and I personally am not at that level of detail with neutrons and couldn't care less (effectively) about neutron wavelengths (although probably I should). Anyway, I told my friend that my kid would be working with neutron beams, which generated the question from my friend, chemist to chemist (since we think about mass spec), "How can you focus neutrons? They have no charge."
I answered, "You can't."
A short time afterwards my kid and I were chatting on the phone and he told me all about the "big" magnet they have in the lab where he's working, which is a 14 Tesla magnet and we got to talking and he reminded me that neutrons have a magnetic moment (thus proving that they cannot truly be elementary particles).
So there's that.
Anyway, in my lazy head, I kind of thought that the upper limit for magnets was in the neighborhood of nine or ten Tesla, and I was impressed to hear that I was wrong, but I had no idea of how wrong I was.
I recall the first time I saw a "high temperature" super-conducting material; it was at an ACS local section meeting in San Diego where the speaker, whose name I've forgotten, brought a Dewar of liquid nitrogen (the "high temperature" as compared to liquid helium in most superconducting magnet systems) and some tiny little disks. He soaked the disks in liquid nitrogen, applied a current to them and did some levitation experiments using a strong conventional magnet.
At that time in my life, I was inclined to have unrealistic fantasies of the type where wind turbines in North Dakota powered Southern California using superconducting power lines.
The rap on this lanthanide/copper oxide "high temperature" superconductors was #1 that they could only carry a low density current before breaking down and #2, that they were ceramics and could not be drawn into wire.
Scratch that, well, maybe not a wire, but a tape...
From the (open sourced) abstract:
Strong magnetic fields are required in many fields, such as medicine (magnetic resonance imaging), pharmacy (nuclear magnetic resonance), particle accelerators (such as the Large Hadron Collider) and fusion devices (for example, the International Thermonuclear Experimental Reactor, ITER), as well as for other diverse scientific and industrial uses. For almost two decades, 45 tesla has been the highest achievable direct-current (d.c.) magnetic field; however, such a field requires the use of a 31-megawatt, 33.6-tesla resistive magnet inside 11.4-tesla low-temperature superconductor coils1, and such high-power resistive magnets are available in only a few facilities worldwide2. By contrast, superconducting magnets are widespread owing to their low power requirements. Here we report a high-temperature superconductor coil that generates a magnetic field of 14.4 tesla inside a 31.1-tesla resistive background magnet to obtain a d.c. magnetic field of 45.5 tesla—the highest field achieved so far, to our knowledge. The magnet uses a conductor tape coated with REBCO (REBa2Cu3Ox, where RE = Y, Gd) on a 30-micrometre-thick substrate3, making the coil highly compact and capable of operating at the very high winding current density of 1,260 amperes per square millimetre...
...and some more from the text of the paper...
Besides its no-insulation construction, the magnet design is mostly conventional, as described in Methods. Table 1 summarizes the key design parameters of our REBCO tape and magnet. The magnet (Fig. 1), named ‘little big coil’ (LBC), consists of a stack of 12 single pancake coils (hereafter ‘pancakes’) wound with 4.02-mm-wide and 43-?m-thick REBCO tape. The tape is composed of a thin 30-?m-thick Hastelloy C-276 substrate, 1.5 ?m of REBCO, a thin silver coating and a final hermetic 5-?m-thick electroplated copper stabilizer, manufactured by SuperPower, Inc. Such thin substrate tapes only became available recently but they immediately attracted our attention because they could enable a very compact and mechanically strong winding. The effective Young’s moduli E shown in Table 1 benefit greatly from the high ratio of Hastelloy (E = 210 GPa) to Cu (E = 100 GPa) content of the winding.
The coil was the third in a series of LBCs, with LBC1 reaching 40 T, LBC2 attaining 42.5 T and LBC3 achieving 45.5 T, all in the same 31.1-T background field and all with nominally the same design. We found that tests in liquid nitrogen were valuable for checking joint resistances and establishing key operation parameters, including the coil constant, the characteristic coil resistance, Rc, and the charging time constant12,13,14,15. Occasionally some joints were remade to reduce resistive losses and minimize coil warming during test. For the high-field test, LBC3 was placed in a 37-mm-diameter liquid helium cryostat inside the resistive background magnet (50-mm warm bore, 18 MW, 31.1 T) at the National High Magnetic Field Laboratory (MagLab). To mitigate trapped helium bubbles, which allow heating of the magnet above 4.2 K during charging16, a small-diameter tube above the magnet periodically pumped away helium vapour during the test so as to limit the temperature of the top surface of LBC3, which reached 7 K at the moment of the 45.5-T quench. A Hall sensor calibrated up to 44.8 T in the 45-T hybrid magnet was used to measure the centre field, together with a pickup coil (the linearity of which was confirmed in multiple charging tests before the main 45.5-T test).
Some pictures from the paper:
The caption:
Left, principle of the no-insulation technique. Centre, construction design of LBC (not to scale). Right, Photograph of LBC. Owing to the no-insulation technique, any dissipative region is bypassed by current transfer to adjacent turns. Because of this vital ‘current-sharing’ feature, electrical burn-out—often observed in ‘insulated’ high-field HTS coils—was not observed after the 45.5-T quench, even at the extremely high conductor current density of 1,420 A mm?2.
The caption:
A calibrated Hall sensor was used up to 44.8 T, and a pickup coil (the linearity of which was confirmed by multiple charging tests before the main test) was used above 44.8 T. LBC3 reached 45.5 T before it quenched at a current of 245.3 A, a conductor current density of 1,420 A mm?2, a peak magnetic stress of 691 MPa and a total strain of 0.38%.
The caption:
Left, Measured voltages. Right, Simulated voltages. The simulation used a previously validated lumped circuit model26. The quench was initiated at DP6 and propagated inductively very rapidly (simulation, 1.46 m s?1; experiment, 1.75 m s?1, almost that of a low-temperature superconductor magnet). Although LBC3 suffered no over-temperature or burn-out during quenching, it did experience mechanical overstrain that we believe is avoidable, as noted in the text.
Quenching the current however led to some degradation of the tapes.
The caption:
a, Transport critical current Ic versus position x of the 12 tape lengths before (black) and after (red) the test. B‖c indicates that B is perpendicular to the tape plane. b, Two-dimensional remnant magnetization maps show the transverse tape uniformity; more uniform (red) tape indicates less damage. 10 of the 12 tapes in Fig. 4a show sharply reduced Ic(x) as x increases, whereas the tapes of pancakes P2 and P11 are undamaged. The figure shows that the dominant damage pattern is one-sided, especially for end pancakes P1, P3, P4, P10 and P12. Pancakes P2 and P11, which have slit edges facing the magnet centre, exhibit essentially no longitudinal or transverse damage.
The caption:
The images show the inner and outer (with respect to the magnet centre) conductor edges of P1 and P2. Slit-edge damage is visible in both pancakes, but that on the outer edge of P1 is about three times deeper than that of P2, which has its not-slit edge facing outwards. The inner edge of P2 is typical of as-delivered tapes. The damage in P1 is the cause of the asymmetric Hall probe scans in Fig. 4b, whereas P2 has an essentially symmetric flux pattern, indicative of uniform current flow uninterrupted by propagated crack damage.
Some concluding commentary:
As we show in Extended Data Figs. 1, 2, subsequent tests of these coils in the same 31-T magnet fully support the interpretation that orienting the damaged, slit edge towards the interior of the magnet suppresses in-service cracking of the REBCO layer. Accordingly, we believe that the 45-T LBC may be capable of even higher fields when proper attention is given to the positioning and quality of the slit edges. We conclude that, although this test magnet cannot yet be considered as a working user magnet, it does provide a viable route to ultrahigh-field superconducting magnets made from copper oxide high-temperature superconducting conductors.
Cool...or hot...
Well, you get the idea.
I trust you had a very pleasant Wednesday.
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