
Plasma physicist discusses the Wendelstein 7-X stellarator - Anchor
http://phys.org/news/2016-02-plasma-physicist-discusses-wendelstein-x.html
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threeseed
"We had to search every corner of Europe to find a company that could mill the
segments of the central ring with such accuracy. In the north of Italy we
found CLP, a family business in a small village"

Such amusing imagery. When you think of small villages in Italy you tend not
to think of them having companies with the ability to do such cutting edge
engineering.

~~~
theoh
This is the company:
[http://www.officineclp.it/en/](http://www.officineclp.it/en/)

Northern Italy has its own character, so maybe not so surprising to find
precision engineering.

~~~
simonebrunozzi
Trust me, Italy is FULL of highly talented engineers, mechanics, etc, and
small companies like CLP.

Unfortunately for them, they're not the best at selling their services
globally.

Source: I am Italian.

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2Pacalypse-
Very interesting interview about very interesting topic.

One minor complaint: answer to the second question seems to have
missed/ignored the question? I assume the true answer lies in the fact that
the technical realization of the stellarator are even more complex than that
of a tokamak and there is more global experience with tokamaks.

~~~
scythe
I can give this a shot. There is a sort of simpler explanation of what happens
in a stellarator, or at least, why the shape is so weird:

When a plasma is confined in a torus, it is spinning (naturally). However,
this creates an effective centrifuge, which means that the hottest atoms --
which are also the "lightest" \-- will move towards the outside of the ring,
and ultimately will escape confinement. This cools the plasma.

The stellarator solution is basically to turn the torus into a Möbius strip,
so that ions which have drifted outside are naturally shuttled to the inside
(for the same reason that the "inside" and "outside" of a Möbius strip are the
same). However, in order to retain rotational symmetry, the strip has five
twists, rather than just one (the topology remains the same).

Unfortunately, calculating the dynamics of a plasma shaped like this is hard
-- really hard. It requires good computers, so for many years stellarators
were mostly an object of theoretical interest. Additionally in order to deal
with other instabilities the Wendelstein has an even more refined shape than
the five-twisted strip.

ITER was conceived in 1987, and at the time it was necessary to go with a
technology that was well-tested and understood, and which people felt
confident would perform as expected. At that time, using a stellarator made as
much sense as writing Firefox OS in Rust or something.

~~~
yourapostasy
Thanks for a layman-lucid explanation. Does the Polywell design also fit into
the overall fusion research picture as yet another design that might one day
contribute parts of itself to the final working design as the Max Planck
director suggested would happen with the tokamak and stellarator designs?

~~~
scythe
The polywell is an interesting concept, but it is extremely different from
every other confinement mechanism, so it's hard to see how the ideas could be
incorporated. To be precise, there are two "shapes" of "electromagnetic
fields": curl-free (electric (unless magnetic monopoles exist)) and
divergence-free (magnetic or electric), and each kind of field lends itself to
a different kind of degree of symmetry in a confinement mechanism.
Specifically, a divergence-free field cannot admit a spherical confinement
because of Green's theorem, whereas a curl-free field requires a very
unrealistic charge configuration to generate a toroidal confinement.

Tokamaks use a combination of divergence-free magnetic fields and divergence-
free electric fields to make a donut. Stellarators use only magnetic fields to
make a twisted donut. The polywell uses curl-free electric fields generated by
an electron gun to make a sphere. There are other variants of inertial
electrostatic confinement fusion, including that currently under development
by Lockheed Martin, but it's generally received less attention.

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melted
I wonder what's up with Lockheed's reactor prototype at this point. This is
some truly badass engineering, but the complexities involved inevitably make
you wonder if there's an easier way. "Only Germans can build it" does not bode
well for mass production worldwide.

~~~
extrapickles
Since this is a research reactor, they probably had to make more structural
compromises to accommodate more sensors, injection ports, etc than what a
power plant version would need. I bet once they played with it for a few years
they would have s better idea of what they actually need for a more practical
version.

~~~
melted
This design is fundamentally hard, I don't think the removal of ports will
make it much simpler. Same with Tokamak. Lockheed's design (as disclosed) is
much simpler. OTOH Lockheed's design is also vaporware until they publish
their experimental data. They've supposedly done hundreds of firings by now,
but haven't disclosed any data.

