Wendelstein 7-X stellarator getting ready for the next phase of operation [pdf]
ipp.mpg.de
ipp.mpg.de
Wendelstein's goal is to find out the viability of the stellarator concept, to see if it could be on par with the Tokamak concept, which so far have shown a better ratio of energy invested and energy won back, but come with their own bag of problems.
What the folks at Wendelstein are doing is a step by step verification of some of the hypothesis. There is this excellent 3h podcast with the scientific leader of Wendelstein [0], unfortunately it is in German. It is fascinating to hear their story on how they build this ultra complex piece of kit. The current change is the shielding of the vessel, which now permits higher energy levels and longer runs. Their long term goal is to operate at 100m K for 30 min.
Regarding the "when we should stop trying" and "it is 30 years out" adage: There has been great progress made in improving the ratio of energy invested and energy won back, the G-factor. Right now no fusion reactor is crossing the G > 1 limit. But Iter would be design to yield about G = 5. Newer designs using high temperature superconductors could even yield G > 10 with a smaller footprint. For more on the current state of fusion research, this video [1] from MIT is fantastic, albeit 1h long.
that said I'd much prefer all the money being burnt on ITER/tokamak would be better spent by spreading the bets into exploring concepts like W7 or inertial confinement or even MIT ARC kind of efforts. Grand efforts like ITER are just ensuring fusion is always 30 years out.
My personal prediction is that we'll have fusion positive yield within a decade of when alternative energy becomes a significant portion (say 25% .. & growing) of total energy mix.
It may be that we can only get fusion power generation working in huge reactors like ITER. It's also a good attempt at getting many countries working together. Ideally, more big brains working together will have better ideas and results.
There's downsides to ITER too of course. But I think it's worth working on.
They are critical in physics research, some medical treatments, fusion research, ... their is absolutely no even remotely practical alternative to them (they're microwave sized devices, using 4-10kw of power that replace synchotrons. Small synchotrons are basketball-field sized and need their own power station) (replace should be taken with a grain of salt since most places that have IEC fusors had no way in hell to afford a synchotron, so they are democratizing fast neutrons. Okay, that's perhaps a strong word but if you have a use for them, there's no reason why you couldn't operate one of these devices in any regular office)
(ps: given how easy, hard to detect, and deadly mistakes with fast neutrons are, please do do it in an office building at least 100m away from me. As it stands though, they're completely unregulated)
The reason we scale up is roughly:
1) Scaling laws work in favor of Q. Q should scale with something like the 3rd power of the size of the reactor. So it's much easier to build a huge Q>1 reactor.
2) Where to stick parts ? Fusion reactors require strong magnetic fields and the only real way we knew of doing that 20 years ago when these were designed was cyronically frozen. That means we need sections inside the reactor for superconductors, for crygenic cooling equipment (mostly piping).
Even disregarding that, fast neutrons will destroy any material they touch, making it brittle and crumble. Aside from bigger reactors making sure more material can get destroyed without failure, one thing that they interact with well is large volumes of water. So if at all possible, we'd like large volumes of water inside the reactor too (for other reasons too, like one strategy for extracting power). That needs space, obviously.
3) It is much easier to keep things stable if their scale is larger. There is more reaction time for the control equipment, the fields involved are larger and move slower, ...
There is a separate engineering problem about how to keep the plasma vessel from warming the magnets (which need be near absolute zero). In the Wendelstein this works by putting most of the device inside a vacuum, to provide better thermal isolation. So the full system is a vacuum chamber which contains the magnets which wrap around the plasma vessel which wraps around the plasma.
There is an article about the cooling system here: https://www.ipp.mpg.de/ippcms/eng/presse/pi/02_10_pi
None, because we haven't achieved G > 1 yet. :)
Per https://physics.stackexchange.com/questions/70209/how-is-ene..., hydrogen fusion produces helium and neutrons; neutrons are unaffected by magnetic fields, so they escape confinement and impact the reactor walls, heating them. The heat is simply vented in current test rigs, but in a working model it can be used to produce steam to power generators. That's specifically for tokamaks, but I would guess the process is similar for stellarators.
But first, designs would have to be able to keep the containment pressure/temperature much higher than it currently is.
https://en.wikipedia.org/wiki/Aneutronic_fusion#Energy_captu...
A Shame these guys are the least funded contender in this race and could do their research on a rounding error from ITAR.
One way to convert the heat from radioactive decay into electricity is through thermocouples (typically found in RTGs used on deep space probes and Mars exploration craft). They're incredibly inefficient though, less efficient than simply turning steam turbines.
I propose we make a reactor large enough to use gravitational confinement and get the energy out via electromagnetic radiation. We could make it safe by having it operate in vacuum at a safe distance from the earth.
I suppose it could work, we would just need to be careful about atmospheric composition to manage radiative cooling, and block some harmful em frequencies. But I don't foresee any problems with that.
The density of the plasma determines the rate of fusion, and is itself determined partly by temperature. If we were to reflect a significant fraction of the emitted radiation back, then the plasma and its surrounding gas should expand, reducing pressure on the fusing core. That should in turn reduce the rate of fusion, lowering fuel consumption.
In theory, we could even diffuse the entire hydrogen supply into a warm cloud that is not dense enough to fuse at all, and store this until we need more heat. As the system cools, it will contract, eventually reigniting itself.
Even if we fail and die, it will still reignite itself, which clearly demonstrates the inherent safety of my proposal.
He didn't really say it won't work, he mostly just said it wouldn't be as clean as people think it will be. But you are right, it does put news like this one into perspective.
Link to the HN discussion from two days ago: https://news.ycombinator.com/item?id=14202488
And if the thing happens to be rotated even by a milli-arc, for example due to asteroid strike or a simple software error, the receiving area will be fried by microwave. Or hackers might want to introduce a deliberate rotation to use it as an orbital based frying weapon. No thanks, that's way too risky.
The actual failure case to be worried about is that the reactor blows up towards the end of its life cycle.
It would act as a switch, where, as soon as the incoming beam stops, the feedback stops and the orbital transmitter would stop too, e.g. if the energy beam went out of position.
http://www.world-nuclear-news.org/NN-Tokamak-Energy-turns-on...
They only switched it on for a 'glow discharge test', but hey:
https://www.youtube.com/watch?v=YNrhTYhUXJc
Reactor teardown, sort of:
Are there fundamental limits that prevent these designs from producing a commercially profitable neighborhood reactor for, say $1 million?
Actually, what's the smallest scale possible for these stellerators? Can one be produced table-top sized, to say, power a ship or train or even a car?
So many questions...
The scale is mostly limited by magnetic field strength. With ordinary superconducting magnets they get pretty big (the planned ITER reactor will weigh 5,116 tonnes). Some people say that new high-temperature superconductors will enable stronger magnets and hence smaller reactors (http://news.mit.edu/2017/brandon-sorbom-designing-fusion-fut...).
(I don't know if there's a problem with my reading comprehension or what?)
In preparation for the next operation phase (OP 1.2a), which is scheduled to start in late summer of this year, the limiter structures have been replaced by a test divertor and all graphite tiles on the baffles and wall protection elements have been installed. This will allow the use of more heating power and access to the required magnetic field configurations.
Looks like they're about halfway along with preparing the graphite tiles for the next phase (4500 out of 8000).
(from: https://hardware.slashdot.org/story/12/04/11/0435231/mit-fus...)
oh and no its not too late. if you have cheap and plentiful energy from fusion you can take on massive geoengineering projects to reverse global warming. its a whole another ballgame!
Just imagine if everybody on Earth has a personal, nearly free 10 megawatt generator. Flying cars. Laser weapons. Direct desalination of seawater in coastal cities. Stomping around in powered exoskeleton suits.
Anyway, it would be awesome. But where do we put all the heat?
Also, if you have plentiful energy you can build way cheaper orbital launch tech. translation you are not bound to earths gravity well anymore. So its not too far fetched to imagine living in space habitats (forget mars that just good for gravity). those will be much better at dissipating waste heat (volume/surface area thing).
Like I said its a whole another ballgame.