
Fusion energy hurdle swept aside - jot
http://news.bbc.co.uk/1/hi/sci/tech/8485669.stm
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lutorm
" _One of many_ fusion hurdles swept aside", would be a less sensationalist
headline... It seems they aren't even at break-even yet, so it's not like we
can start building power plants this decade...

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gjm11
Not only are they not at _breakeven_ yet. Unless I've misunderstood badly,
they haven't even got _fusion_ occurring yet.

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DaniFong
Fusion's been occurring in other reactor designs since the 50's -- just not
specifically in this particular reactor. High School kids have achieved fusion
in their basement with Farnsworth Fusor type designs. It's not especially
hard.

Breakeven, though, is a lot tougher.

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Retric
We have passed "break even" conditions in a reactor for D-T for a few seconds.
The real test is getting useful amounts of net energy generation which
requires about 5x break even for several minutes.

IMO, ITER's design should get to that point, but I don't think fusion is going
to cost less than solar let alone coal for a long time.

PS: Using lasers to create fusion has always been more about simulating bombs
than it was creating useful amounts of energy.

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DaniFong
You have achieve breakeven more broadly -- over the entire pulse, or over the
electricity you pull from the grid, or perhaps most properly, including all of
the material and labor costs as compared to just taking heat from the fusion
reactor in the sky with wind turbines and solar collectors.

As for the simulation of bombs vs power, I think it depends on who you ask;
scientists or DOE project managers?

It's interesting, after having left a PhD program in plasma physics (for
fusion power,) I have a very different sense of the commercially plausible.
All we're really using the fusion for is to create heat, and there are many
ways to get heat inexpensively (solar, geothermal, coal, natural gas) that
don't involve temperatures of hundreds of millions of degrees, that don't
require superconducting coils, liquid helium cooling systems, ultra-high
precision machined tungsten tiles, structural materials that are vaguely
defined, completely unsourced, untested at the correct neutron fluxes, and
rely upon rare earth elements, liquid lithium systems from which we're
supposed to do tritium recovery (lithium is really reactive, tritium bubbles
up and is explosive and diffuses through walls and embrittles them), liquid
lithium _walls_ on the inside of the chamber; high vacuum vacuum pumps, giant
particle beams and incredibly non-linear and poorly understood science. You're
comparing that to coal and mirrors and holes drilled in the ground and wind,
all of which ultimately go into some kind of turbine (which is half or most of
the expense!) The benefit of fusion just doesn't seem worth it for anything
other than military applications or interstellar spacecraft. And really, we've
got a lot to worry about before then...

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Retric
As I recall the actual limitations where two fold, it's a research device so
they did not want the extra radiation produced from an actual DT reaction so
they stuck with DD. And it was cheaper to build it as a pulsed device and let
it cool down, vs having an active cooling system.

From what I can tell the problem over the last 25 years with fusion is people
keep saying what is the least amount of money we can spend and still make
something useful. But, actually building a fusion reactor costs ~20 billion so
we have been stuck prototypes when we need to shoot for the moon.

EDIT: Taking JET's design
(<http://en.wikipedia.org/wiki/Joint_European_Torus>) and building a 10GW
reactor would actually be easier than trying to build a 1GW reactor with the
same basic design.

Also <http://en.wikipedia.org/wiki/JT-60> "During deuterium (D–D fuel) plasma
experiments _in 1998_ plasma conditions were achieved which would, if the D–D
fuel were replaced with a 1:1 mix of deuterium and tritium (D–T fuel), have
exceeded break-even"

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DaniFong
I would like to argue that prototypes have been what's called for. We don't
even have a clear idea of what a commercial fusion reactor would look like.
The cooling and tritium production issues, the structural materials, and the
lifetimes required of the super cooling and superconducting systems, are
massive problems that haven't really been solved yet.

It's possible that replacing D-D with D-T would have yielded break-even for a
few seconds, (I've heard that claim before too) but I'm very skeptical;
increasing the internal heat generation is sure to change the plasma
conditions: for example, there would be a lot of adiabatic expansion, which,
even restrained against the tokamak fields, is liable to have a variety of
unstable modes.

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Retric
I feel that with a modular design that includes remote handling capability you
could test things out a lot faster on a full scale device. As to internal
heating issues, I don't think there is much problem extrapolating from Q0.7 at
JET to Q1.2 at JT-60.

Large Plasma devices are "the sexy" but IMO it's just another engineering
problem at this point. And you don't design large scale power plants to sit at
the outer edge of their capabilities 24x7. So yes, the highest energy pulses
are unable after a few seconds, but we have built steady state fusion reactors
they just operate further from their limits.

PS: Finding T is a problem, but "just build it bigger" and suddenly D-D (or
75%D - 25%T etc) becomes reasonable.

Edit: I am suggesting building building something with 4x ITER's budget which
should give you ~8x the plasma volume and a lower surface area to volume ratio
etc. We can also pump of the field strength etc. But you are limited to how
much heat the wall can take so the plasma conditions don't need to be as
efficient.

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DaniFong
Hi Retric,

I do agree that the problem of controlling Q > 1 plasma becomes easier as you
increase the volume. However, I don't think that's the biggest problem. As you
yourself point out, you're limited in how much heat the wall can take. This is
fundamentally the limiting factor in fusion power plant designs, unless a much
more efficient direct conversion scheme is feasible. Why not instead take the
tungsten panels you'd use and point a bunch of mirrors at it, achieving the
same heat flux? Mirrors are just not that expensive.

PS: Do you work in fusion, by the way?

PPS: We should chat more. Send me a message at dfong at lightsailenergy.com

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jackfoxy
I hope some good science and engineering are coming out of this, because
American taxpayers have been pouring money down the fusion rat-hole for over
40 years. From my ignorant layman's perspective, I just don't see recovering
more usable energy than the energy put in happening. It's been "30 years away"
for the past 40 years.

Not everything is a matter of time. I'm not saying man's ingenuity won't
figure it out, but the only place nuclear fusion takes place in nature is in
stars, and that's powered by the pressure of a huge amount of mass, which can
never be recreated on Earth. There has never been a goal-oriented technology
project that has lasted this long, spent this much treasure, and produced so
few results. Even brilliant people can engage in wishful thinking.

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jcdreads
Imagine a single thermonuclear explosion: one big enough to destroy a large
city. The bomb doesn't weigh that much compared to the amount of energy
released. A gigantic amount of energy comes from a small amount of mass. The c
__2 in Einstein's formula is the speed of light squared; it's a really huge
number.

As for the wisdom of the NIF as public policy, that's something on which
reasonable people can (and do) disagree. I'd only point out that the first
government to master the goal of break-even fusion (getting more energy out of
the reaction than is put in to trigger the reaction) will gain a _ridiculous_
economic advantage over the rest of the world, to say nothing of the non-
economic benefits of energy independence. It's the kind of big bet that rich
nations can (and in my opinion should) take.

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delackner
Would their advantage really be all that big? Modern nuclear fission reactors
can produce tons of energy and you can reprocess the fuel, providing what
seems to me like energy independence available _today_.

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bioweek
I've always wondered why we can't just blow up hydrogen bombs in a giant
underground chamber and extract energy from the heat produced.

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delackner
Much safer to just run a nuclear reactor. But I wonder... would a fission
explosion-based reactor even be possible, let alone more efficient? I don't
think so...

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bioweek
A nuclear reactor uses fission. My idea uses fusion triggered by fission (look
up how hydrogen bombs work). Fusion is much more efficient that fission which
is why my idea has merit.

