Boron availability

[Tulse]

But are there significant advantages to making it spherical, or even cylindrical? What is the efficiency loss relative to the ease-of-construction of something like a box?

[belbear]

The advantage of a sphere over any other shape is that every part of the collector receives roughly the same intensity of radiation, assuming the plasmoid is in the centre.

Using depositing techniques to create a thick structure consisting of so many layers will encounter some serious roughness issues. Any uneven deposit creates a rough surface, and in a sputtering or vapor coating technique, the tiniest unevenness amplifies itself. (the tops always catch more new material than the valleys)
Making it increasingly difficult to ensure the conducting layers do not make contact somewhere and short circuit.

AFAIK, it has only been done with micron-thin layers, as in semiconductors, not a multi-inch-thick shell.

[Breakable]

I think its much to early to talk about the onion, and especially its design. Its yet to be proven as a x-ray to electricity converter. I believe it is possible to reach 50-60-70-maybe even 80 % efficiency in this conversion, but it is probable the final device will look nothing like the onion, especially when no efficiency has been demonstrated yet (as far as i know).

[Aeronaut]

Breakable wrote: I think its much to early to talk about the onion, and especially its design. Its yet to be proven as a x-ray to electricity converter. I believe it is possible to reach 50-60-70-maybe even 80 % efficiency in this conversion, but it is probable the final device will look nothing like the onion, especially when no efficiency has been demonstrated yet (as far as i know).

While I agree that the final form may not even resemble an onion, all of those layers (donkey) and our existing convention make it a good name. It also helps counter the sterile scientific sounding nomenclature of the FF and Polywell projects, imho.

I also believe that the best time to begin solving a challenge, especially one as big as the onion’s engineering, is well before funding and trying to build anything along those lines. Nothing to gain by approaching the engineering phase(s) like a cram session the night before a final exam.

Nor would I expect early onions to have impressive stats- the first performance breakthroughs may well be adding 125 or 250kW to the previous best performance level.

[vansig]

belbear wrote: The advantage of a sphere over any other shape is that every part of the collector receives roughly the same intensity of radiation, assuming the plasmoid is in the centre.

Using depositing techniques to create a thick structure consisting of so many layers will encounter some serious roughness issues. Any uneven deposit creates a rough surface, and in a sputtering or vapor coating technique, the tiniest unevenness amplifies itself. (the tops always catch more new material than the valleys)
Making it increasingly difficult to ensure the conducting layers do not make contact somewhere and short circuit.

AFAIK, it has only been done with micron-thin layers, as in semiconductors, not a multi-inch-thick shell.

But do we actually have the same intensity of radiation? or is the radiation pattern anisotropic?

Aren’t structures thicker than irregularites, and separated by xray-transparent insulative material, presumably of sufficient thickness that short-circuits don’t happen?

[Aeronaut]

I get the impression that the thin foil layers are at or a micron or few thick, and that a production onion could be less than 1 mm thick. That’s why I keep insisting that we’re going to need some variation of CVD- and we’ll probably need custom tooling as well.

[Author]

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