Laser Fusion

[Darth Wong]

Did you research this claim at all before making it? Hydrogen-boron fusion is even better than D-T fusion in this regard, because it works with ordinary hydrogen (you don't even need deuterium) and the most common isotope of boron (~80% frequency, currently refining ~2 million tonnes of boron a year).

Sorry, I've never bothered researching H-boron fusion because it's not considered one of the leading candidates for commercially viable fusion. There's a shitload of fusion ideas out there that nobody can envision scoring break-even.

Tritium on the other hand is extremely rare, which is why practical D-T power station concepts require lithium blankets that 'breed' tritium via neutron capture (with the associated mechanical complexity of capturing and storing it).

I tend to think in the context of a Canadian. We have a lot of tritium because our fission reactors make it as a waste byproduct.

However hydrogen-boron requires roughly an order of magnitude more ion energy than D-T and has only a third of the reaction rate at the same density. He3 is rare on earth, but it's a lot more common than tritium or even lithium to breed tritium with in the universe in general, so He3 fusion wins for sci-fi concepts (D-D fusion beats He3-He3 for reactant abundancy, but it's much more difficult - pure hydrogen fusion would be the best but AFAIK it's essentially impossible to use in a reasonably compact reactor).

How the fuck would pure H-H fusion be the best? The energy yield from pure H-H fusion is terrible. As I said, the literature is chock-full of wonderful fusion concepts that work fine except for the small problem that they'll never achieve break-even.

[Starglider]

There's a shitload of fusion ideas out there that nobody can envision scoring break-even.

True, but hydrogen-boron is one of the two best candidates for aneutronic fusion, and has reasonable prospects for eventually achieving break-even. Unlike the wilder ideas there is actual directed research going on towards it. It won't be in the first generation of fusion power stations or likely the second, but a single order of magnitude increase in energy is within the realm of plausibility, and this may eventually be a good choice for mobile applications that need to minimise shielding weight and radioactive waste production.

(D-D fusion beats He3-He3 for reactant abundancy, but it's much more difficult - pure hydrogen fusion would be the best but AFAIK it's essentially impossible to use in a reasonably compact reactor).

How the fuck would pure H-H fusion be the best? The energy yield from pure H-H fusion is terrible.

It's the 'best' solely in terms of reactant abundance; the universe is full of normal hydrogen. A purely theoretical advantage as deuterium is relatively easy to separate out and we're not likely to run out of it in the foreseeable future. As I say, the reaction rate for p-p-p-p is so low for any plausible reactor conditions that it's pretty much worthless for powering anything smaller than a star.

[Sikon]

He3 is rare on earth, but it's a lot more common than tritium or even lithium to breed tritium with in the universe in general, so He3 fusion wins for sci-fi concepts

The concentration of helium-3 in Jupiter and the other gas giants is very low, like parts per billion. In general, helium-3 is not so much as a millionth of total helium. Helium-3 fusion might be developed someday, perhaps, though more difficult than deuterium-tritium fusion to get working at all, but it doesn't win on availability of fuel.

It could be unfortunate to choose such a rare isotope when otherwise space solar power or thermonuclear power would not tend to run into troubles like nations squabbling over who gets to skim off the trace helium-3 on the moon. The amount is usually estimated as on the order of a single million tons, while the moon's surface area is millions of square kilometers, with past solar wind deposition of helium-3 presumably spreading it over the area, so many square kilometers of lunar surface have to be processed per small number of tons of helium-3. For nuclear fuels in general, there are billions of tons of uranium affordably extractable from seawater, versus the amount of helium-3 on the lunar surface usually estimated as on the order of a single million tons, versus trillions of tons of deuterium in earth's oceans alone, plus thousands of quadrillions of tons of deuterium in Jupiter and other gas giants. If ever developed, helium-3 might be the one kind of nuclear power actually having fuel costs be a large component of total expense.

The D-T fuel cycle takes only deuterium and lithium as fuel inputs since the tritium is produced and then consumed in the process. Deuterium is a number of orders of magnitude more abundant than helium-3. Lithium is far cheaper than even deuterium, being a few dollars a kilogram; even lithium-6 is 8% of total lithium, likewise cheap.

Historical thermonuclear bombs have typically been built with primarily lithium-6 deuteride, an exception being the first hydrogen bomb, the Ivy Mike, that used liquid deuterium. A small amount of tritium is used in thermonukes, taking advantage of it being easiest to ignite first.

[Starglider]

The concentration of helium-3 in Jupiter and the other gas giants is very low, like parts per billion.

True, but AFAIK the concentration of lithium in gas giant atmospheres is zero. I don't know how abundant it is in asteroids and moons though.

Lithium is far cheaper than even deuterium, being a few dollars a kilogram; even lithium-6 is 8% of total lithium, likewise cheap.

Though it will be as expensive as anything else you have to ship from earth in a sci-fi setting (significant in hard sci-fi, probably not in softer sci-fi) unless it can be mined from the abovementioned asteroids and moons.

[Einhander Sn0m4n]

Any promise for this polywell thingamajigger that Robert Bussard invented? His site has a bevy of PDFs explaining the concept, as does that Wikipedia article. He claims Boron-Proton fusion capability, as well as fusion rates that go up at the seventh power of the size of the device. Unfortunately it appears the Navy pulled funding in 2k5 just as the device started producing solid results, due to the Iraq War.

[Einhander Sn0m4n]

Gegh, can someone fix that first link?

[Admiral Valdemar]

Thanks, Sikon, that post was, as ever, highly informative. The reason I doubted AM initiated fusion was because, although in the past I saw it as highly possible within a couple of decades given dedicated manufacturing projects, Starglider and others led me to question whether it was all that practical in reality(I still envision Asimov Arrays covering large swathes of arid land converting solar into energy to then be stored as AM products), given the inherent inefficiency, the lack of decent RF traps that could store any particles for longer than a few days and were not exactly portable currently. Actually, I meant to include a query as to how efficient future AM containment devices could be and what would be the best medium for storage e.g. anti-protons, positrons or anti-lithium or what have you.

The excavator you mentioned was on my mind though. Given their power requirements they do act as plug-in appliances of large scale, but I was thinking we could have something like the SheVa gun in the future. Phongn knows what I mean, a pebble-bed powered 16" cannon wielding tracked monster with AM tipped sabot rounds for all your anti-alien invasion needs.

Ein: I've been interested in such boron based fusion too, though no one seems to really be interested. One of the reasons is because I saw it as being more applicable to a RAIR drive for interstellar travel, given the original Bussard ramjet design is now seen as incapable of dealing with bremsstrahlung related drag and the hydrogen count within our little bubble in the galaxy may be too low anyway. Course, if you can get a magnetic monopole made, you would have a far better job of making such a drive than even boron catalysed fusion, but this is still highly theoretical.

[Einhander Sn0m4n]

Ein: I've been interested in such boron based fusion too, though no one seems to really be interested. One of the reasons is because I saw it as being more applicable to a RAIR drive for interstellar travel, given the original Bussard ramjet design is now seen as incapable of dealing with bremsstrahlung related drag and the hydrogen count within our little bubble in the galaxy may be too low anyway. Course, if you can get a magnetic monopole made, you would have a far better job of making such a drive than even boron catalysed fusion, but this is still highly theoretical.

All well and good, but the only thing this has to do with a Bussard Ramjet is its inventor.

This is a series of magnetic dipoles (toroidal electromagnet coils) arranged in a rough sphere to confine electrons to a point (virtual cathode) in the center, causing the ions to, in effect, go "WHOOPEE LET'S ALL FLING OURSELVES AT THE CENTER!" and cause fusion. It's in effect a gridless version of a Farnsworth Fusor.