
Wendelstein 7-X stellarator getting ready for the next phase of operation [pdf] - clon
http://www.ipp.mpg.de/4206699/013_April_2017_eng.pdf
======
shaqbert
Wendelstein 7-x is really not fusion research, but plasma physics research. At
the energy/temperature levels and magnetic field strength this machine is
operating, plasma is showing all kinds of undesirable behavior, such as
turbulence, radial forces... a little bit like the storms on Jupiter. This
imposes many challenges, because as soon as the plasma escapes the magnetic
field and touches the vessel, it rapidly cools - ending any potential fusion.

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.

[0]: [http://alternativlos.org/36/](http://alternativlos.org/36/)

[1]:
[https://youtu.be/L0KuAx1COEk?t=37m23s](https://youtu.be/L0KuAx1COEk?t=37m23s)

~~~
DesiLurker
almost all of fusion development is basically plasma physics research. nuclear
fusion itself is known science, its the plasma containment & stabilizing that
hard. so you can sustain the fusion & get positive yield.

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.

~~~
zlynx
There really are physics that only work at very large scale, such as stars and
black holes.

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.

~~~
candiodari
There are fusion reactors that are 5 cm diameter. Total size less than a
microwave. They're very useful but not energy-positive, though there are
reports of one that was Q=0.2, which given that that one was fridge sized was
pretty good. They're the only practical way we have of producing fast
neutrons.

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, ...

------
phkahler
And just the other day we had a link here where a retired physicist was saying
fusion is not likely to work, and if it does it will produce radioactive waste
much like fission.

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.

~~~
nick_
What if we made a really really huge one? I'm talking 15 × 10^28 kg worth of
hydrogen. At that size it would start and maintain itself. We could place it
far enough away that we could harness its output safely here on earth with
solar cells!

~~~
Will_Parker
The problem is, something that massive would affect the motion of the Earth
itself.

~~~
RealityVoid
I think it was a joke hinitng at the sun, but it seems to be @ 1 order of
magnitude off, so I'm just confused now.

~~~
nick_
I was going for the smallest amount of hydrogen that would form a star. I
suppose the joke would be improved if I used a number measuring the Sun's
initial hydrogen content. I suppose that's why I'm not a comedian :P

------
twic
Meanwhile, in boring-shaped fusion reactor news, boringly-named Tokamak Energy
switched on their new reactor, the ST40, today:

[http://www.world-nuclear-news.org/NN-Tokamak-Energy-turns-
on...](http://www.world-nuclear-news.org/NN-Tokamak-Energy-turns-on-
ST40-fusion-reactor-28041701.html)

They only switched it on for a 'glow discharge test', but hey:

[https://www.youtube.com/watch?v=YNrhTYhUXJc](https://www.youtube.com/watch?v=YNrhTYhUXJc)

Reactor teardown, sort of:

[https://www.youtube.com/watch?v=jRyUWOUk_48](https://www.youtube.com/watch?v=jRyUWOUk_48)

~~~
boznz
Thanks for the links

------
mozumder
So, assuming these work great.. what are the next steps to get fusion energy
production?

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...

~~~
vilhelm_s
The smallest scale is basically the same as for tokamaks (the advantage is
that you can operate a stellarator continuously, while a tokamak is pulsed
which may be less convenient for power generation).

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...](http://news.mit.edu/2017/brandon-sorbom-designing-fusion-
future-0123)).

~~~
mozumder
looking more into this, it looks like the minimum size limit is the wall that
absorbs the free neutrons from the De-Tr reactions. It looks like it'll always
be some minimum size due to the energy of the released neutrons.

------
mrfusion
What's the next phase? When does it start?

(I don't know if there's a problem with my reading comprehension or what?)

~~~
clon
From the source:

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.

------
colonelxc
Home page for the project, which provides some higher level details:
[http://www.ipp.mpg.de/w7x](http://www.ipp.mpg.de/w7x)

------
mandelken
only 10 years too late..

~~~
Gravityloss
The earlier, the better. Can someone say at what point we should stop trying?

~~~
rb1
The point when the black line on the graph goes below 0
[http://i.imgur.com/sjH5r.jpg](http://i.imgur.com/sjH5r.jpg)

(from: [https://hardware.slashdot.org/story/12/04/11/0435231/mit-
fus...](https://hardware.slashdot.org/story/12/04/11/0435231/mit-fusion-
researchers-answer-your-questions))

~~~
nomercy400
That only explains why the Wendelstein 7-X isn't being made in the US.

------
janemanos
Back in the sixties some scientist said "Fusion is ready in 20 years", then in
the eighties some others said it again, and in the 2000's the next ones... but
hey, I don't care how long it will take as long as humankind strives for such
stuff I'm fine

