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 Post subject: The Trouble Wth Fusion
PostPosted: Thu Feb 04, 2010 11:18 am 
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http://forums.somethingawful.com/showth ... id=3262710

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This is mainly about ITER.

Quote:
- High-power gyrotrons to generate ~200 GHz waves reliably and efficiently, for electron cyclotron heating (ECH) of the plasma
- Mirrors that can reflect ECH waves while not getting cloudy from neutron damage
- A reliable system to detect and mitigate major disruptions
- A way to get in and repair broken parts in the machine when it's been neutron-activated by the fusion reaction going on inside

All of these things are being actively worked on in fusion research labs. But there is a lot of development left to be done. I'll post more about this later, because it's really important, but there is a huge gulf between even ITER, which runs for about 10 minutes at a time, to a true reactor, which has to run at 10 times the power density of ITER, and for a year at a time with no interruptions.

Here is some interesting backstory about "technology" vs. "science". At one time, the fusion research program in the U.S. was run out of the Department of Energy's, well, energy program. Then, in the mid-1990s, the world basically decided they'd just about had enough of the broken promises from the various fusion research programs. This led to the cancellation of the entire Canadian program, and nearly did in the U.S. as well. The only way it was saved was by moving its 'home' within the government funding system to the DOE Office of Science; the same agency that funds particle accelerators like Fermilab.

Thus the fusion research program became a "science" project rather than an "energy" project. Everyone working on it still does it because it might one day solve our energy problems, but the program no longer had to justify itself to Congress in terms of progress towards actually making energy. When this happened, funding for basic science was ramped up, and for "fusion technology" like magnets, almost completely cancelled. So in the U.S. there has been very little development of practical fusion technology for the last 15 years; most of that stuff is now being developed in Europe, Korea, and Russia. American labs have made phenomenal progress forward on understanding plasma physics issues (transport, stability, etc.) but haven't focussed as much lately. on actually engineering parts for a reactor.

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PostPosted: Thu Feb 04, 2010 11:52 am 
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From the same link:

Quote:
High-temperature superconductors that can remain superconducting at higher magnetic fields than today's superconductors, are able to be disassembled for maintenance, and can withstand some neutron damage. (This is a huge one, I can't overstate this.)


I have that one aced.

Quote:
Figure out how to make a material wall that won't get eroded away by the hot plasma that is always coming into contact with it. Especially at the "divertor strike points" where we want the plasma to hit, so that we can exhaust the helium "ash" from the fusion reaction.


That is pretty simple in a Polywell. You cool the alphas by direct conversion and then the heat load is tolerable. Doing that in a tok is hard because the alphas are cooled by thermal interactions with the plasma. Ans even if you could get them from the edge the direct conversion machine would be huge because a tok is ALL edge. Not to mention the thermal energy distribution.

Quote:
Develop faster control systems that can maintain the plasma very close to the stability limits, without disruptions occuring


Control systems I know one or two things about. Sensors too. You can't control what you don't know.

Quote:
Figure out a way to drive the required plasma current without a big inductor up the middle of the tokamak. (This is absolutely essential, since there is no such thing as a steady-state tokamak without non-inductive current drive.)


He mentions a number of other problems I have left out of the list. The physics for Polywell may be more difficult. The engineering is much easier.

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PostPosted: Thu Feb 04, 2010 2:59 pm 
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Joined: Tue May 13, 2008 10:22 am
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Location: The Netherlands
Quote:
One last note on the Polywell: you cannot read about it without repeatedly seeing the name M. Simon. This is some crazy retired electrical engineer ... has made it his mission to evangelize the Polywell online and in magazines....

Reverend M Simon?
In "Passion of the Polywell"? :D

But he sounds overall positive about Polywell, but makes a point of not stating it as such. He mentions a pro and a con research.
Not talking negative about a competing project sounds to me like a compliment, but I could be projecting here.

He does seem to mix taking shots at Simon with compliments about his personality. Trying to discredit Simon's scientific opinions, while not trying to look like an a-hole in the process.


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 Post subject:
PostPosted: Thu Feb 04, 2010 5:03 pm 
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Location: Rockford, Illinois
vernes wrote:
Quote:
One last note on the Polywell: you cannot read about it without repeatedly seeing the name M. Simon. This is some crazy retired electrical engineer ... has made it his mission to evangelize the Polywell online and in magazines....

Reverend M Simon?
In "Passion of the Polywell"? :D

But he sounds overall positive about Polywell, but makes a point of not stating it as such. He mentions a pro and a con research.
Not talking negative about a competing project sounds to me like a compliment, but I could be projecting here.

He does seem to mix taking shots at Simon with compliments about his personality. Trying to discredit Simon's scientific opinions, while not trying to look like an a-hole in the process.


I don't mind at all. I get the same shots around here from time to time. And I must admit some of them are true.

What I liked overall is that he actually studied Polywell some before stating his criticism.

And I must say that it was one of the best expositions on the problems of ITER I have read.

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PostPosted: Thu Feb 04, 2010 7:18 pm 
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Posts: 181
Location: UK
If a well-established Expert says something is impossible, he --Why so often a 'He' ?-- is probably wrong.

If a well-established Expert says something will cost more and take longer, he's usually right...

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I've grown up with fusion 'just a decade away'. Like 'economic access to space', I hope it will be *this* decade. At least RE's Skylon/Sabre have a sporting chance. Based on the output/volume power curve, I'd rate the Polywell route as better than even...


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