A couple decades ago there was a plan to build something called
the SuperConducting SuperCollider near a town named
Waxahatchee, in the state of Texas, USA. See link. It was
funded
for a few years of initial construction, and then abandoned. If
it
had been finished, there would have been
an underground
mostly-
circular tunnel about 87 kilometers in circumference (lots
bigger
than the existing Large Hadron Collider).
A bit more than 1/4 of the tunnel was built before the project
was
canceled. I'd like to see it finished, not because we might put a
big particle accelerator in there, but because we could put a big
nuclear fusion reactor in there. There's a particular fact about
magnetic-confinement fusion reactor designs that just begs to
be
put into a circular tunnel with a nicely lengthy circumference.
A fair number of experimental fusion-research devices have
been
built in the shape of a torus or doughnut. See 2nd link. Any
torus has
two significant measurements. One is the overall diameter of
the
ring ("major diameter"), and the other is the diameter of the
tube
that forms the ring ("minor diameter"). In the linked images
you
can clearly see that the major diameter is only a few times
larger
than the minor diameter. This is mostly a result of limited
funding.
Here at the HalfBakery we sneer at limited funding, and I've
actually mentioned this Idea before, in annotations of a
completely different Idea (see 3rd link). I decided this Idea
needed to be presented independently, partly because of a
couple
recent developments.
The first thing involves a type of fusion reactor design called a
"stellarator" --see 4th link. You will note that a torus is
involved,
and here the major diameter is significantly larger than the
minor
diameter. There are two reasons for that.
See the 5th link for a depiction of a simple toroidal magnetic
field. It is easy to tell that the magnetic field is a lot more
concentrated in the middle of the torus, than on the outside of
the
torus. In a magnetic-confinement fusion reactor, that area of
weakness invites the plasma to escape confinement, and shut
down the reactor. Not good!
Well, the larger the major diameter of the torus, the more that
the outside magnetic field will be similar in strength to the
inside
field.
Next, in a stellarator the confined plasma moves through the
tube, flowing in the big major-diameter circle. Specially
designed magnetic fields force the plasma to "twist", so that it
spends part of its time near the inner region of the torus, and
part
of its time near the outer region of the torus. The net effect is
that it stays confined more easily, experiencing an averaged-
strength magnetic field. Building those twisty magnets is
easier
when the major diameter of the torus is numerous times larger
than the minor diameter.
Well, the Waxahatchee tunnel can hold a decent-sized minor-
diameter tube, but the major diameter is so much vaster that
we
might not even need twisty magnetic fields to keep the plasma
confined. If so, its design would be significantly simplified.
The other recent technical advance involves the manufacturing
of
significant quantities of high-temperature superconductors
(only
need liquid nitrogen to keep it cool enough to superconduct).
See
the 6th link.
I really think we are getting really close to building practical
nuclear fusion power plants. If THIS one was built, it likely
could
power a pretty sizable chunk of the entire USA.