

Magnets for fusion energy: A revolutionary manufacturing method developed - da02
http://www.eurekalert.org/pub_releases/2014-07/nion-mff072514.php

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mng2
The big thing about this is that it's achieved using so-called High-
Temperature Superconductor material, where the superconducting transition
temperature is basically anything higher than the < 10ish K that conventional
superconductors require. HTS such as YBCO have several attractive properties
besides their less-cryogenic operating temperature such as higher max current
per area (the 'critical current density'). But since HTS are generally ceramic
in nature, they can't be straightforwardly worked and extruded to form wire in
the way that 'conventional' metallic superconductors like NbTi can.

So what they're proposing is to make relatively small sections of cable which
can be made by simple stacks of conductor. Then they'll join them together in
the final assembly by soldering. This of course is much easier than trying to
wind one massive coil in one go, but now you have a plethora of
conventionally-conducting joints between sections, which will heat up under
operation. They argue that removing some additional heat at the HTS operating
temperature of 20 K is preferable to having to cool to 4 K for conventional
superconductors, which sounds reasonable.

However I feel that this is tough to support on the mechanical front.
Energized magnets want to move, and you can't let them move because that leads
to heat production, which leads to quenching. You need structure to keep them
from moving. So in addition to the electrical connections, you need lots of
structural steel and welds. You've got a bunch of stuff in there with
different expansion coefficients, so making it work out in practice should be
challenging. The LHC program was set back over a year due to overheating in
one bad magnet splice.

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whatshisface
To put 100,000 amperes in perspective, that's about a 10x-above-average
lightning strike, like the one that hit right before the launch of Apollo 15.

The reason this is significant is because the current was flowing through a
superconductor, and so would flow forever (well, forever-ish). Imagine the
biggest bolt of lightning you've ever seen, and then imagine it going around
in circles inside a loop about the size of a person.

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ingenter
What's important is not only maximum current, but magnitude of the magnetic
field. Yes, these quantities are closely related, but fusion reactors are
interested in dense magnetic field, and superconductors often break down after
some magnetic field. For example, according to this site, the record is 17.6
Tesla - [http://www.kings.cam.ac.uk/news/2014/world-superconductor-
re...](http://www.kings.cam.ac.uk/news/2014/world-superconductor-record.html)

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radarsat1
Sorry, high-temperature super conductors are a thing?

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JoelHobson
Yes, and they have been for a long time, although probably not as high-
temperature as you're imagining. Wikipedia has an uncited claim that the high-
temperature label applies to anything over 30K, which is still extremely cold.

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youngButEager
Fusion is big. Fusion could be economically/societally dangerous. If fusion is
developed very incrementally no big deal.

If a real breakthrough occurs making fusion cheap and easy, a huge chunk of
economic activity could be made redundant overnight.

Huge social unrest, starting in the middle east and U.S. to a lesser degree is
possible as incomes vanish.

Hopefully will replace fossil fuels incrementally, just as the transistor
replaced the vacuum tube incrementally, etc.

A huge breakthrough in affordability and practicality could be dangerous
though.

By publishing their results to the broad masses it will be hard for concerned
governments to discredit them.

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AnthonyMouse
> Fusion could be economically/societally dangerous.

Fusion is the opposite of that. Cheap energy is the greatest driver of
economic growth and social prosperity the world has ever known. The fact that
fossil fuels are becoming increasingly expensive and at the same time
destroying the global climate is nothing short of an unmitigated disaster.
Anything legitimately capable of reducing energy costs while fighting climate
change is rightly hailed as an economic and social miracle.

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fennecfoxen
Yes. Widespread deployment of nearly-free power would save a lot of households
a lot of dollars on heating, cooling, and electric costs. It would save web
hosting companies a lot of money. After a few years of additional electric-car
development, it'd save them fuel costs too. It would go a long way to solving
the California drought (desalinization becomes much more attractive).

All that money could be spent on something else that's actually meaningful
instead of on oil-extraction infrastructure and the fortunes and lifestyles of
Saudi Arabian oil princes.

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zachrose
It's crazy to think through the ramifications of fusion power. A Sahara
irrigated with desalinated water. Mining trash to get the metals out.
Sequestering CO2. Turning the entire globe into a climate-controlled mall.

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lotsofmangos
One problem to watch out for if you have effectively unlimited power, is that
global warming would no longer be an indirect effect of stuff like CO2, but
just a direct result of not caring about efficiency any more.

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zachrose
Can't you just crank up the AC and blast the heat into space somehow?

