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Compact nuclear fusion reactor is 'very likely to work,' studies suggest

nytimes.com

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Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#21

Post by mabbo »

tesseract wrote: post #15
maxcan wrote: post #6

Earlier quoted context omitted.

Just like the alcubierre drive!

The "Alcubierre drive" isn't an engineering design for a method of propulsion. It's just a nickname for a certain valid solution of the Einstein field equations. Like, in classical terms, you can get a repulsive force to come out of Newton's law of gravitation if you plug in a negative mass. But that doesn't mean you've designed a hoverboard.

> But that doesn't mean you've designed a hoverboard.

Must we spoil all my dreams?

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#22

Post by opwieurposiu »

isoprophlex wrote: post #8

I never quite understood the math behind power densities in a fusion reactor. In the sun, isn't energy production occurring at something like 100-1000 W/m3? So, if you want to build a multiple MW fusion plant, shouldn't these plants be ridiculously huge compared to, say, a wind turbine rated at a couple of MW? Is the density of the plasma so much higher in a fusion reactor? Also, something else I never grokked, how d…

The temperature at the center of the sun is about 15million kelvin. The plasma temperature of a fusion reactor is around ten times higher. Also, a rector uses deuterium–tritium (D–T) fusion, and the sun uses hydrogen fusion. D-T requires less confinement and is more energetically favorable. If DT is like setting off a fire cracker then hydrogen fusion is like igniting a damp log.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#23

Post by willis936 »

cultus wrote: post #14
jjoonathan wrote: post #9

Earlier quoted context omitted.

Superconductors recently got much better in a way that has cubic effect on reactor size.

I know essentially nothing about superconductors, but if they all have essentially zero resistance, what makes one better for this application? I thought the main advantage of high-temp superconductors was using liquid nitrogen instead of helium.

HTS coils would still be run with liquid helium for higher critical current and higher magnetic field.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#24

Post by elil17 »

isoprophlex wrote: post #8

I never quite understood the math behind power densities in a fusion reactor. In the sun, isn't energy production occurring at something like 100-1000 W/m3? So, if you want to build a multiple MW fusion plant, shouldn't these plants be ridiculously huge compared to, say, a wind turbine rated at a couple of MW? Is the density of the plasma so much higher in a fusion reactor? Also, something else I never grokked, how d…

You're correct, that's a good ballpark for the average heat generation rate in the sun. However, 99% of heat generation in the sun occurs in the core (approximately the center 25% by radius) and this area is much more energy dense. Further, fusion reactors could achieve an even higher volumetric heat generation rate then the sun's core does.

To collect energy, heat would be transferred to a working fluid (e.g., molten salt) by exposing that fluid to the hot plasma. Then the working fluid would be used to boil water and spin a turbine.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#25

Post by smaddox »

cultus wrote: post #14
jjoonathan wrote: post #9

Earlier quoted context omitted.

Superconductors recently got much better in a way that has cubic effect on reactor size.

I know essentially nothing about superconductors, but if they all have essentially zero resistance, what makes one better for this application? I thought the main advantage of high-temp superconductors was using liquid nitrogen instead of helium.

High temperature superconductors provide more stable resistance-free conduction than traditional superconductors. If both are cooled to liquid helium temperatures, that increased stability translates to being able to sustain a higher magnetic field. Higher magnetic fields provide tighter plasma confinement and higher density, which allows for much smaller fusion reactors.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#26

Post by mensetmanusman »

cultus wrote: post #14
jjoonathan wrote: post #9

Earlier quoted context omitted.

Superconductors recently got much better in a way that has cubic effect on reactor size.

I know essentially nothing about superconductors, but if they all have essentially zero resistance, what makes one better for this application? I thought the main advantage of high-temp superconductors was using liquid nitrogen instead of helium.

Think of it as the amount of energy you can store in a superconductor.

This is talked about in terms of the ‘phase diagram for superconductors’

http://www.supraconductivite.fr/en/index.php?p=supra-levitat...

As you put more current in the supercondutor, eventually you break it and it leaves the mode, as it gets hotter, likewise, as the magnetic field gets stronger, likewise.

You want the largest ‘area under the curve(s)’ to handle more and more ‘superconductivity’

New materials are enabling this which has the cubic effect mentioned for reducing confinement volume and making things more affordable and increasing energy densities that can be contained, etc.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#27

Post by rsynnott »

isoprophlex wrote: post #8

I never quite understood the math behind power densities in a fusion reactor. In the sun, isn't energy production occurring at something like 100-1000 W/m3? So, if you want to build a multiple MW fusion plant, shouldn't these plants be ridiculously huge compared to, say, a wind turbine rated at a couple of MW? Is the density of the plasma so much higher in a fusion reactor? Also, something else I never grokked, how d…

The actual fusion in the sun happens in only a small part At the middle. The rest is just there to provide mass :)

> Also, something else I never grokked, how do you get the power out? The plasma heats up, but how do you turn that into useful electrical energy?

Steam turbines; same as fission or coal. Or gas turbines, if you want to get fancy.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#28

Post by willis936 »

magicalhippo wrote: post #10
Someone wrote: post #4

“Sparc takes advantage of a newer electromagnet technology that uses so-called high temperature superconductors that can produce a much higher magnetic field, Dr. Greenwald said. As a result, the plasma is much smaller.” So, is this ‘just’ a matter of ITER being obsoleted by improvements in magnet tech before it is completed, or is there more in this design than scaling down ITER?

There's some discussion about this in this[1] presentation which also mentions the SPARC reactor. My main takeaway is basically yes, high-temp superconductors got "mainstream" very quickly. I'd recommend watching the whole thing, I found it quite interesting. [1]: https://youtu.be/L0KuAx1COEk?t=2929

It’s important to keep in mind that MIT is working hard to monetize HTS coil production. There are some unseen hush hush politics at play here.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#29

Post by DesiLurker »

Someone wrote: post #4

“Sparc takes advantage of a newer electromagnet technology that uses so-called high temperature superconductors that can produce a much higher magnetic field, Dr. Greenwald said. As a result, the plasma is much smaller.” So, is this ‘just’ a matter of ITER being obsoleted by improvements in magnet tech before it is completed, or is there more in this design than scaling down ITER?

yes thats true. ITER is obsolete already because it actually cannot use these high-temp-high-Tesla superconductors. at the moment ITERs best hope is that it 'proves' that fusion is viable & then do a full redesign for DEMO to do proper scaled operation.

here is the original presentation by Dr Whyte of MIT behind this Sparc project: https://youtu.be/KkpqA8yG9T4?t=1511

he talks about the impact of these newer magnets at around 26min mark.

Re: Compact nuclear fusion reactor is 'very likely to work,' studies suggest

#30

Post by aaronblohowiak »

eigenhombre wrote: post #5

Having read about tokamaks for thirty years, I'd be curious what specific breakthroughs and innovations have occurred since the 1980s, which lead to the optimism described in the article (which is otherwise frustratingly devoid of detail). It's great there are seven-peer reviewed articles about SPARC, but plasma was not my specialty in physics -- would any specialists care to comment on whether there is anything part…

so you get the plasma spinning and you have two problems: containment and instability. better magnets and faster control systems are the two big things that (in my layman's-bad-at-physics understanding) have really advanced in the last decade.
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