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Wed Jun 12, 2019, 08:44 PM

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-μm-thick REBCO tape. The tape is composed of a thin 30-μm-thick Hastelloy C-276 substrate, 1.5 μm of REBCO, a thin silver coating and a final hermetic 5-μm-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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Reply Record High Magnetic Field (45.5 Tesla) Achieved Using High Temperature Superconducting Ceramic. (Original post)
NNadir Jun 2019 OP
AJT Jun 2019 #1
Thomas Hurt Jun 2019 #2
NNadir Jun 2019 #3
eppur_se_muova Jun 2019 #4
NNadir Jun 2019 #5

Response to NNadir (Original post)

Wed Jun 12, 2019, 08:52 PM

1. Well, my reation after reading this is that I like cheetos, both crunchy and puffed..

Basically, I don't understand most of what you wrote, but I am eternally grateful that people like you exist. The rest of us would be lost without you.

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Response to NNadir (Original post)

Wed Jun 12, 2019, 10:01 PM

2. Fusion reaction containment?

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Response to Thomas Hurt (Reply #2)

Thu Jun 13, 2019, 06:15 AM

3. Yes. Fusion reactors contain plasmas, charged particles.

Charged particles in a magnetic field move effectively in a circular motion depending on their speed, BXv.

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Response to NNadir (Original post)

Thu Jun 13, 2019, 03:04 PM

4. I had a chance to visit the National High Magnetic Field Laboratory back in '78 or '79 ...

... back when it was housed at the Francis Bitter Magnet Laboratory at MIT. (It was then known as the Francis Bitter National Magnet Laboratory; somebody in Congress decided that "elite" universities shouldn't monopolize National Labs, so they moved it to, um, Northeast FL, which is just crawling with the technically educated professionals you would want to hire at such an institution, unlike stuffy old Cambridge, MA.) I recall that in some projects they were using high explosives to compress magnetic field fluxes to obtain transient magnetic fields of very high strength, at the expense of destroying the sample being studied, and part of the instruments doing the studying. Haven't kept up with the highest *steady* magnetic fields achieved by more conventional means, but knew it was getting into the ridiculous range.

A visit to the Francis Bitter {not National} Magnet Laboratory Web site shows they seem to be mostly an NMR center these days. When I was there, they had two 40-ton flywheels in the basement which could supply 8 MW of DC power in two-second bursts to be released when they needed it for particularly power-sucking magnets. Unfortunately, the rumble of the wheels caused laser apparatus to vibrate noticeably even on the uppermost floors. I guess that's all moved to FL, or outmoded, now.

The folks down in FL seem to have taken over the area of magnet development that started at Bitter, and are advertising a 100 Tesla (pulsed) magnet in development. Thats one million Gauss, if you want to make it sound even more impressive. Maybe they'll start using megagauss instead of Tesla soon. (Earth's magnetic field is ~~ 1/2 Gauss, for comparison.)

(While Googling for background info, I came across a surprisingly personal account of the history of FBNML which attributes the relocation to academic infighting. It is found here: https://henrykolm.weebly.com/mit-magnetic-lab-1961-82.html )

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Response to eppur_se_muova (Reply #4)

Fri Jun 14, 2019, 10:33 PM

5. Thanks for that interesting bit of history; I enjoyed reading about this.

To be quite frank, I haven't thought all that much about magnet technology, I always got what I needed from straight up 1D NMR at around 360 MHz, and my interaction with the magnets was basically being annoyed with myself to no end when I forgot to take my wallet out of my pocket when loading the sample, which demagnetized all of my credit cards and ATM cards.

I have sort of lazily assumed that the most powerful magnets were all superconducting, and your links and discussion made me realize that I was missing quite a bit, particularly knowing about Francis Bitter.

For NMR, I can't say I've ever been particularly involved in 2D experiments like COSEY, NOESY, etc.

I'm an old guy.

I had some peripheral interest in magic angle spinning when I was in school in connection with the time scales of non-classical carbocations, but I never went in any deeper other than to say I've been there.

Last summer my son got to visit the NMR facility at the Sorbonne, where, during a tour conducted by Christel Gervais he was exposed to lots of solid state heteronuclear stuff; apparently there's a lot going on with that involved in an interesting new take on ceramics, specifically polymer derived ceramics, to manipulate these concepts to highly ordered nanostructures. He didn't get to submit any samples there, however. Apparently there's a lot of magic angle spinning stuff involved with that. (I really should read some of Dr. Gervais' papers, but there is so much to learn and so little time left in my life.)

I do attend lectures at PPPL every winter for the wonderful "Science on Saturday" series, and always one or two talks are marketing for fusion.

Although I'm a fission kind of guy; I would like to see fusion work; if only to have access to those high energy neutrons that surely can do a lot of fun things that would be useful to humanity. One fact that always troubled me about fusion was the reliance on superconducting magnets, and the requirement that we have some of the coldest stuff on earth, liquid helium, in close proximity to some of the hottest stuff on earth, a fusion plasma, with no real avenue to control the direction of those high energy neutrons.

Thus the most exciting thing in this paper in the OP for me was to read about the "high temperature" superconducting magnets, which makes superconductivity viable at liquid nitrogen temperatures.

That, I think, is a big deal; and the fusion people, I hope, have looked at this paper.

Helium is not a renewable resource, and we are going to run out of it, and although a fusion reactor would be making some, and we can get helium-3 from tritium, we're talking gram scales, not ton scales, because of the extraordinarily high energy density of fusion plasmas, even in comparison to fission nuclei.

Thanks again for the illuminating comment.

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