polywell reactor for booster rocket applications?

Discuss how polywell fusion works; share theoretical questions and answers.

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93143
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Postby 93143 » Sat Apr 25, 2009 8:22 pm

I can't imagine how a system like that could maintain a hard vacuum against tens or hundreds of atmospheres of pressure. Especially if you had to momentarily shut down the reactor for anything... Remember that these concentrated alpha streams cannot be allowed to touch any surface, because they're at a kinetic temperature of 20 billion degrees and contact WILL result in local damage regardless of cooling. This means that neutrals from the working fluid could easily slip around the core alpha flow and enter the chamber. Furthermore, in this scheme there are streams exiting at points all around the reactor; one per cusp. That's a lot of potentially heavy hardware, and a lot of engines that all have to work continuously if the reactor is to not choke...

It just seems ugly. Am I missing something here? It seems to me that it would be far easier and lighter to just use direct conversion (you've got to solve the neutral pumping problem anyway) and pipe the resulting high voltage current into the engines. That way you have no problems with vacuum seals, focused alpha beam impingement, multiplication of small engine modules (or worse, an attempt to pipe either fast alphas - that aren't all at the same speed! - or hot propellant from all around the reactor to a single engine/nozzle)...

On the other hand, if it does turn out that your way works better for some combination of reasons, so be it...

Regarding low-voltage electron guns, it's not feasible. You'd have to step down 6 GW from ~1.5 MV to whatever low voltage you're talking about, and you can't do that inside anything resembling an aerospace mass budget. For lower power requirements, like pumping the LH2 or running the reactor, you could use a heat engine powered by a mini-REB, but most of the power has to be used as is - HVDC - or else you're wasting a LOT of mass.

[An elaboration on my previous post: I forgot to mention that the required engine temperature is too high for any known substance, by a large margin. Since the nuclear lightbulb principle cannot be used here, this disallows wall-separated direct heating and leads to the requirement of some form of energy injection.]

I think there's a reason Dr. Bussard chose REB heating for high-pressure high-thrust modes, and direct ejection of alphas with small supplementary mass flows ("Diluted Fusion Product") for the long-range ultra-high-Isp deep space mode. As MSimon has noted, the things Dr. B said typically turn out to have had a fair amount of thought put into them. I've already tried and failed (twice) to invent a better atmospheric engine system than ARC-QED, and I am therefore of the opinion that this case is another example of Bussard knowing what he was talking about.

Also realize that the fusion output -> propellant heating efficiency of a REB engine is pretty much 100%, because it's "All Regeneratively Cooled". This means that any energy produced by the reactor that doesn't wind up in the electron beam is already in the propellant by the time the beam blasts it - including any refrigeration power necessary to get the propellant flow rate down to an optimum level...

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Postby D Tibbets » Sun May 10, 2009 3:30 am

To error is human... and I'm very human.

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Postby Rick Kwan » Mon May 11, 2009 2:52 am


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Postby 93143 » Mon May 11, 2009 3:22 am


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Postby Roger » Mon May 11, 2009 4:14 am

I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

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Postby Rick Kwan » Mon May 11, 2009 4:15 am


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Postby Rick Kwan » Mon May 11, 2009 4:25 am


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Postby Rick Kwan » Mon May 11, 2009 4:30 am


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Postby 93143 » Mon May 11, 2009 5:34 am


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Postby Rick Kwan » Mon May 11, 2009 6:31 am


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Postby djolds1 » Mon May 11, 2009 6:54 am

Vae Victis

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Postby 93143 » Mon May 11, 2009 8:01 am


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Postby Rick Kwan » Mon May 11, 2009 2:22 pm


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Postby Roger » Mon May 11, 2009 5:14 pm

I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

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Postby 93143 » Mon May 11, 2009 5:16 pm



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