Zeljko Vujovic - it is a good question Even though Tc of MgB2 is just 39K, not 390K, it may be one of the most promising material for next generation superconducting coils. The higher-Tc materials are 2D oxides with very complex and expensive technologies for tapes and films. Maybe one should look towards multiple cryogen-free cryocooler-based magnets. One example is from Quantum Design: https://qdusa.com/products/versalab.html

Winding in the form of solenoid is used for making superconducting magnets which are suitable for magnetic field in the range ~1 T to ~10 T. The making method of the superconducting magnet has been more or less well established with few avenues for improvements and that's why only NbTi and Nb3Sn are chosen superconductors. NbTi is used up to 5T and for fields ~10 T the chosen superconductor is Nb3Sn.

Zeljko Vujovic - you may be interested in following this project too: https://indico.cern.ch/event/659554/contributions/2708372/attachments/1525993/2386079/3P1-01_Huub_Weijers_Room_1.pdf

"Before this new magnet reached full field in December 2017, the world's strongest superconducting user magnet had a field strength of 23.5 Teslas. At 32 teslas, this new record-holder is a whopping 8.5 Teslas stronger than the previous record – a giant leap in a technology that, since the 1960s, has seen only baby steps of 0.5 to 1 Tesla... Begun in 2009, the project represents a breakthrough in superconducting magnet technology on many fronts. Among other innovations, it combines low-temperature superconductors commonly used in today’s superconducting magnets - niobium tin and niobium titanium -- with “YBCO,” a superconducting ceramic composed of yttrium, barium, copper and oxygen. Although YBCO-coated conductors in this case operate at the same temperature and in the same helium bath as their metallic counterparts, they remain superconducting far above the practical magnetic field limits inherent to niobium-based superconductors. For this reason, YBCO can also be called a high-field superconductor; it superconducts at far higher temperatures than niobium-based materials but, like all superconductors, performs best at very low temperatures.

When it becomes available to users, the 32 Tesla will be the first high-field magnet available to researchers to incorporate YBCO, a finicky material a few commercial companies have been developing for years in collaboration with MagLab engineers and scientists. The 2.3-ton magnet system features about 6 miles of YBCO tape, formed into 112 disc-shaped “pancakes.” Two inner coils of YBCO, fabricated at the MagLab are surrounded by a commercial outsert consisting of three coils of niobium-tin and two coils of niobium-titanium."

https://nationalmaglab.org/magnet-development/magnet-science-technology/magnet-projects/32-tesla-scm

Raivo Stern and Snehadri Bihari Ota

The current situation is such that low critical temperature superconductors are used for the main magnets of MR scanners. To achieve superconductivity, these superconductors require cryogenic coolers, which are bulky and heavy.

Meanwhile, room temperature superconductors have been discovered, which acquire the property of superconductivity without cryogenic coolers. These superconductors, for now, are not usable for making the main magnets of MR scanners.

The following questions are asked:

1. What are the prospects of using room temperature superconductors to make the main magnets of an MR scanner?

2. Can and how can large cryogenic coolers be removed?

Zeljko Vujovic and Snehadri Bihari Ota :

1. There are currently no "room temperature superconductors" suitable for technological applications like magnets;

2. Until usable superconductors "superconduct" at cryogenic temperatures only it is unavoidable to use some sort of cryogenic vessels around them... Still, both the closed cold machine solutions and liquid-N2 only systems should be noticeably smaller and easier to handle.

Raivo Stern

1. Everything you wrote in our discussion is completely true. There are no "room temperature superconductors" suitable for tecnological applications such as magnets.

2. The existence of new high-temperature superconducting materials has been published in the literature:

Tl - 2212, Tb2Ba2CaCu2O8 (Tc =108K),

Bi - 2223, Bi2 Sr2 Ca2 Cu3 O11 (Tc =110K)

Tl - 1234, Tl Ba2 Ca3 Cu4 O11 (Tc =122K)

and others, including room temperature superconductors:

Cd5MgC6 , Tc = 370C(98F/310K) i

Tl5 Sn2 Ba2Si, Tc =420 C(107F/315K).

- What can you say about these "high temperature superconductors" and "room temperature superconductors"?

- Will they, when, how and why will be able to apply or not?

Zeljko Vujovic

Under point 2 I believe you ment:

Tl - 2212, Tl2Ba2CaCu2O8 (Tc =108K),

Bi - 2223, Bi2Sr2Ca2Cu3O11 (Tc =110K)

Tl - 1234, TlBa2Ca3Cu4O11 (Tc =122K)

Those are all quite well known and studied cuprates - typically there is also doping dependence, i.e. O8-x and O11-x, and Tc varies with x.

Tl is knowingly a toxic element, but there are applications using Bi - 2223, also called BSCCO, for wires and coils, see e.g. Article A Feasibility Study of High-Strength Bi-2223 Conductor for H...

or https://iopscience.iop.org/article/10.1088/1757-899X/18/15/152001/pdf ...

As to:

Cd5MgC6 , Tc = 37°C (98F/310K) and Tl5Sn2Ba2Si, Tc =42°C (107F/315K) I'm not aware of such superconductors... Do you have any references?

Raivo Stern

Here are some examples:

- http://www.superconductors.org/rtscvia3.htm

- http://www.superconductors.org/30C_rtsc.htm

- http://www.superconductors.org/28c_rtsc.htm

- http://www.superconductors.org/42c_mod.htm

The starting reference for high temperature superconductors and room temperature superconductors is:

- http://www.superconductors.org/

Do you know any magazine whose scope would cover the topic "On magnets and superconductors of MR scanners"?

Zeljko Vujovic

that site you referred to seems to have disappeared...

There may be some more dedicated Journals, but you may want to start there:

https://mri-q.com/magnets---part-ii.html

Dear Raivo Stern,

Thanks a lot for the reply.

I know the site you recomended to me, and the work of the professor Allen D. Elster. That site is great. I used it. That site was my starting point. Allen D. Elster, on that site, predicted that high-temperature superconductors and room temperature superconductors would replace ecisting solutions. Will, when and how?

I, again, managed to open the site www.superconductirs.org. It is available ro me.

Best regards.

Zeljko Vujovic - thanks I got it open again (there is an "i" instead of "o" in your link). True, there is a page (from 2016) about Cd5MgO6 as a room-temperature superconductor, but over almost 4 years there seem not to appeared any confirming publications in scientific literature... So it is not proven result yet.

When and how the new high-temperature superconductors and maybe even room temperature superconductors would replace existing solutions remains to have seen - I gave you couple of links I'm aware of, but I'm sure there are many more around...