Hacker News Reader

Comment by JustAPerson | Hacker News Reader

https://www.youtube.com/watch?v=KkpqA8yG9T4

Here's a video lecture from the MIT Professor (Dennis Whyte) who was leading the research group that provided some of the key designs for the SPARC reactor. As the NYT article explains, that research has been spun out into a startup that raised $200M.

The key breakthrough is the advancement of REBCO tape superconductors which allow you to (1) generate record breaking magnetic field strengths (2) easily disassemble the super conducting loop for fast repairs / refuels / more modular design.

It's a long talk, but it's extremely fascinating. Basically everything becomes much easier once you can increase the magnetic field strength. This talk is fairly accessible to even relative laypeople who have a vague understanding of E&M physics.

View on HN

Timeline (in case you want to skip over some parts):

00:01:00 - introducing Dennis Whyte, MIT department head for nuclear science

00:04:24 - presentation starts

00:06:00 - identifies breakthrough with REBCO magnets

00:07:25 - explains deuterium-tritium fusion

00:12:30 - basic metrics for reactor performance

00:17:15 - energy output of other previous fusion experiments

00:19:00 - examines ITER and the problems of its approach

00:22:00 - problems solved by high energy magnetic fields

00:28:15 - full scale reactor concept, teardown of REBCO magnets

00:37:00 - design limits and margins

00:39:00 - fixes plasma instabilities found in weaker magnetic chambers

00:40:00 - maintainability, lifespan, component replacement

00:45:00 - solution to neutron damage and energy capture

00:50:30 - cost and profitability

00:54:00 - full graph of field strength vs reactor scale (and thus funding requirements)

01:01:50 - Q&A

01:30:00 - question about the biggest risks

Also a more recent video, with more numbers and even more confidence than the first: https://www.youtube.com/watch?v=rY6U4wB-oYM

I think they're using Yttrium (i.e. YBCO), right? It's hard to find that info.

Buried in the wiki page for YBCO is a note that REBCO is a synonym of sorts. The superconducting tapes that are discussed in the talk thus would seem to be YBCO.

Yes. Re stands for "rare earth," and yttrium is probably the most common one used for ReBCO, but lanthanum is also used.

https://nationalmaglab.org/magnet-development/magnet-science...

Looks like they 'only' need to be at 4.2Kelvin as well to operate, which is a definite improvement

They don't need to be that cold to start superconducting, 4.2K is just the temperature you could expect with liquid helium cooling. It would actually be superconducting with liquid nitrogen but the reason why you would still want to go colder is because superconductors have a maximum magnetic flux that they can sustain while still being superconducting. The current travelling through a superconductor itself also contributes to the magnetic flux so even though it's superconducting there's still a limit as to how much current you can pass through a conductor and how high of a magnetic field you can create. This limit is dependent on temperature though, so you definitely want to use liquid helium so you can create a much stronger magnetic field.

Right. To expand: Maybe someday we can use liquid hydrogen or nitrogen (or even water, depending on progress with hydride superconductors) for these reactors, but a big reason they’re able to make this more compact reactor work is the much higher critical currents/fields that these high temperature superconductors can handle when cooled far below their critical temperature. See: https://fs.magnet.fsu.edu/~lee/plot/plot.htm

The hero we don't deserve.

Another excellent talk for those interested is MIT's Pathway to Fusion Energy (IAP 2017) - Zach Hartwig.

https://www.youtube.com/watch?v=L0KuAx1COEk

He goes into detail about SPARC as well and why a higher magnetic field using HTS superconductors enables performance that can otherwise be obtained by greater size as ITER is trying.

That's a great talk, and really gives me a lot of hope for the SPARC concept that this article is about.

Phenomenal talk! I'm still watching - so captivating.

Reply on news.ycombinator.com