[NoSmoke]

Allan Brewer wrote:

A thought on ion beam conversion efficiency:

It occurs to me that ions traveling through a coil to generate electricity might be analogous to wind passing through a wind turbine. Thing is though, the maximum possible efficiency for a wind turbine is about 59% ie. no more than 59% of the kinetic energy of the wind passing through the turbine’s swept area can be recovered (sometimes referred to as the “Betz law”).

http://en.wikipedia.org/wiki/Betz’_law

What is going on is that the wind must slow when it reacts with the turbine blades but cannot slow beyond a certain velocity as it must keep moving to get out of the way of the incoming wind behind it. It seems to me that a similar situation might exist for a stream of ions traveling down the annulus of a coil or past a coil for that matter. Maybe then the efficiency of ion to electrical energy conversion is similarly limited for the same reason??

That is an interesting analogy. Although it is indeed the kinetic energy which is being harvested from the ion beam there seem to me to be a couple of fundamental differences in our favour. Firstly the cross sections of the ion nuclei are approximately 1e-10 smaller than molecules, so that collisions of decelerated ions with “full speed” ions are much rarer, and secondly, partly-decelerated ions still produce a pro rata voltage in the coil and can theoretically, other things being equal, be decelerated by the induced current right down to zero velocity.

I see what you mean but I wonder if there is another factor to consider. As the ions slow in the coil they will necessarily bunch up at the slow end and, although the ion cross section is much smaller than a molecule, they can still “see” each other via electrostatic repulsion, that repulsion being greater from the bunched up end than towards the coil entrance where the ion density will be lower. Thus the slower ions will tend to slow down the faster upstream ions and the slower ions will have to maintain some velocity to get out of the way, similar to a wind turbine. I think…….

[NoSmoke]

Ivy Matt wrote: After reading the article I’m not certain if they meant Li6/Li7+Be9, or if they meant p+Li6/Li7 and p+Be9. I kind of think it’s the latter. I’m not familiar with any fusion reaction involving Be9 as an input, but I am somewhat familiar with the p+Li6 and p+Li7 reactions. The former produces a He4 ion at 1.7 MeV and a He3 ion at 2.3 MeV, for a total of 4 MeV. The latter produces two He4 ions at a total of 17.2 MeV. Lately I’ve been wondering why p+B11 is seen as the “Holy Grail” of aneutronic fusion, and p+Li7 isn’t. There aren’t any downsides to p+Li7 as far as I can tell, and it should be easier for most confinement concepts to achieve.

Wiki has some info on that:

“Some reaction candidates can be eliminated at once. The D-6Li reaction has no advantage compared to p-11B because it is roughly as difficult to burn but produces substantially more neutrons through D-D side reactions.

There is also a p-7Li reaction, but the cross section is far too low, except possibly when Ti > 1 MeV, but at such high temperatures an endothermic, direct neutron-producing reaction also becomes very significant.

Finally there is also a p-9Be reaction, which is not only difficult to burn, but 9Be can be easily induced to split into two alpha particles and a neutron.”

http://en.wikipedia.org/wiki/Nuclear_fusion

[NoSmoke]

james: That sounds like a reasonable explanation – most (some?) of the input is recovered from the ion beam and the X-rays are gravy.

Ivy: I guess if Learner says heavy ions are more compressible, b-B11 might work better – I hope he’s right.

A thought on ion beam conversion efficiency:

It occurs to me that ions traveling through a coil to generate electricity might be analogous to wind passing through a wind turbine. Thing is though, the maximum possible efficiency for a wind turbine is about 59% ie. no more than 59% of the kinetic energy of the wind passing through the turbine’s swept area can be recovered (sometimes referred to as the “Betz law”).

http://en.wikipedia.org/wiki/Betz’_law

What is going on is that the wind must slow when it reacts with the turbine blades but cannot slow beyond a certain velocity as it must keep moving to get out of the way of the incoming wind behind it. It seems to me that a similar situation might exist for a stream of ions traveling down the annulus of a coil or past a coil for that matter. Maybe then the efficiency of ion to electrical energy conversion is similarly limited for the same reason??

[NoSmoke]

Ivy Matt: My bad – it was p+N15 (and what I read was the Polywell thread so thanks for finding it).

I have read Lerner’s (is that the polite way to refer to him here?) comments that p+B11 goes easier at or around the ideal temperature for that reaction but, does it necessarily follow that D+D (for example) would not be as favourable (as p+B11) at the ideal D+D fusion temperature (i.e. a much lower and presumably easier to reach temperature)? Perhaps it has to do with the greater magnetic field that accompanies the p+B11 fusion conditions (?). Anyhow, that’s why I was wondering earlier if D+D could be a possible fall-back route to take.

Just another wild thought – since blem radiation is generated by the reaction of electrons with ions in a plasma, could it be reduced by stripping some of the electrons from the plasma by some means? I suppose that might increase confinement difficulties but maybe there is a favourable trade-off there. In the spirit of we need everything we can get since, as I understand it from another thread, the max Q that can be expected from the FF p+B11 device is about 1.5(?) which IMO is very uncomfortably close to break-even – we are going to need some very high and perhaps unrealistic energy conversion efficiencies to surpass electrical break-even (and, by a sufficient margin to also surpass commercial break-even). As a newcomer I don’t want to start by expressing negative opinion but I do wonder sometimes what the realistic odds are of actually reaching here such a difficult goal.

james: If the He ions simply spiral around in the plasmoid until they loose their excess energy, how then would then generate net energy when finally expelled from the plasmoid by the magnetic field collapse? It would seem the energy imparted to those ions would only then be obtained from the collapse of the magnetic field which in turn was created by the input energy (which it seems to me would result in no net gain).

[NoSmoke]

Aeronaut wrote: Welcome to FocusFusion, NoSmoke.

Thank you – I look forward to spending more time here.

We’re currently burning D-D to confirm that the machine and sensors are working correctly and reliably, as well as proving as much of the theory as practical in the known regime of D-D fusion. But the fuel of choice is pB-11, make no mistake. Like the PolyWell’s venetian blinds, our coil is likely going to be handling some incredible voltages on every single pulse. Fortunately, 5MW at 1MV works out to only 5A, which should help somewhat.

I would think either high voltages or high amps or something in between (maybe depending on how many turns in the coil(s)). It would still seem advantageous however to keep the voltage, if possible, to levels that could be used m/l directly on-site to minimize conversion costs. I wonder if it is even practical now to convert 1 or 2 MV DC at 5MW to lower AC voltages with currently available hardware?

In any given machine cycle, the p and B-11 ions are crushed into a near-solid form by the collapsing magnetic field, into what we call the plasmoid- a microscopic magnetic bubble which heats and compresses the fuel gasses into the range where fusion pretty much has to happen if science and theory are both right. This eliminates most of the individual fuel ions, replacing them with the helium ion beam and the electron beam leaving the decaying plasmoid from opposing ends, as directed by the magnetic field. The electron beam is somewhat imaginary, since it is absorbed by the plasmoid, further heating it.

Not sure what is meant there – are you saying that the fuel ions are “eliminated” by being (mostly?) converted to fusion products or that they are expelled from the plasmoid by some other means that distinguishes them from the alphas (after only some have fused?).

Didn’t know that p-N14 was an option- can’t remember seeing any threads discussing it.

It wasn’t here that I saw it – could have been the Polywell forum. In any case, as I understand it, the advantage of p N14 is that there are no side reaction neutrons at all. It is the tail end of the CNO fusion process that goes on in large stars but I’m not sure if the final step would actually happen in an earth bound reactor.

N14 + proton -> O15 + gamma_ray
O15 -> N15 + positron + neutrino
N15 + proton -> C12 + He4

I was able to find this (possibly fanciful) description of a CNO reactor designed to power an interstellar spacecraft:

http://projectark.net/projectark/fusion_drive.asp

N14 occurs in the atmosphere in small but usable concentrations so the fuel is there if the reactor can be developed.

One other comment if I may. I have gone through the

“Introduction to the Plasma Focus-
Machines, Applications and Properties
S Lee & S H Saw ”

presentation and have noted there are many plasma focus devices in operation (or were). Yet I did not notice any mention of developing a power producing device – only machines to generate neutrons and gammas etc. or, any mention of p-B11 devices other than the FF effort. I’m wondering then what technology sets the FF project apart from the others?

Thanks Aeronaut for responding to my post…..

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