Which fusion has the most chancess for success?

[chrismb]

Your recognition of my 'balanced' outlook is appreciated!

I will [usually] debate, for example, the non-viability of A and the viability of B with proponents of A or the opponents of B.

Doesn't really matter what my personal views are, I just don't really see the point in debating with people that agree with you; wouldn't that just be "useless" social chit-chat? (An Asperger's type view-point, there!)

[TallDave]

We will release the Polywell data when your world is ready for it.

I LOLed.

[D Tibbets]

Unfortunately, even gravitationally confined fusion only barely works and has a lower specific output than, say, mammalian bodily mass by a couple of orders of magnitude. viz. running a 2m^3 cow is a better power generator than a 200m^3 'stellar' fusion plasma, and grass is easier to obtain as a fuel than tritum, or 11B, to boot.....

Perhaps true for hydrogen (P-P) but I don't think anyone is considering trying to do that on Earth. A better example would be gravitationally confined D-D reactions, or even D-P reactions. I'm guessing that D-D is ~ 10^20 times easier/ faster than P-P. The CNO cycle is intermediate between the two (much closer to D-D if the Star is massive enough).
For that matter how does P-N15 compare to the CNO cycle overall?

Dan Tibbets

[chrismb]

Perhaps true for hydrogen (P-P) but I don't think anyone is considering trying to do that on Earth. A better example would be gravitationally confined D-D reactions, or even D-P reactions.

The thing is, if that were to happen as a dominant reaction then that star where that is happening would super-nova because it is the 'self-regulating' properties of a gravitationally confined fusion core that allows it to work - the hotter it gets, so it expands and the reaction rate drops off. Too much energy will lead to 'too hot' will lead to supernova. This is pretty much exactly what happens - these 'higher power' fusion fuels are hanging around doing essentially nothing at p+p stellar temps, but when the p fuel runs out, the star contracts, gets hotter, and these reactions kick off and the thing goes 'whhoooommfff'.....!

Gravitational confinement isn't strong enough to create the power densities we need on earth. The only terrestrially viable fusion device that is currently known to liberate net energy is pulsed inertial confinement and the only known way to initiate that is with an enormous mechanical compressive detonation (the h-bomb) as the Rayleigh instabilities involved in laser-ICF are currently insurmountable - the timescales of instability are orders of magnitude away from the confinement time required.

[jmc]

In terms of producing net energy, I think ITER or DEMO will get there eventually (JET got pretty close)

Depends on how you juggle and spin the numbers;

best JET DT pulse;
energy into plasma = 22MJ
energy out of plasma = 18MJ

but

energy required to form the magnetic field = 1GJ

total efficiency = 2%

efficiency required = 1000%

Well the coils used in JET were copper as they were cheaper then superconductors, whereas the coils in a fusion power plant will be super conducting. I realise you still have to put in energy to keep them refrigerated but I believe the numbers have been done and its condsiderably less than the fusion energy you get out.

The biggest limitation is the heating you have to put in to drive current non-inductively (1/3 of out put power) and that's assuming your neutral beams are 3 times as efficient as the state of the art.

[chrismb]

Well the coils used in JET were copper as they were cheaper then superconductors, whereas the coils in a fusion power plant will be super conducting. I realise you still have to put in energy to keep them refrigerated but I believe the numbers have been done and its condsiderably less than the fusion energy you get out.

The biggest limitation is the heating you have to put in to drive current non-inductively (1/3 of out put power) and that's assuming your neutral beams are 3 times as efficient as the state of the art.

No, this isn't the 'lost' thermal energy in the coils, this is the energy stored in the magnetic field and would be the same whether generated by copper, SC, or by the thoughts of God himself; that magnetic field has within it 1GJ. ITER's will have around 50GJ, meaning it has to run for over 100s at 500MW just to pay back the energy cost of forming the magnetic field.

As the plasma collapses in JET, and it takes the magnetic field 'with it' (as plasmas do), the whole of the physical torus physically deflects vertically by a few cm (from what I've been told) and in any case you can hear the collapsing field as a big 'thump' (even in the control room behind the multi-metre concrete walls). It's a lot of magnetic energy!!... it's a quater tonne of TNT equivalent!

When ITER's plasma collapses, the magnetic field alone will be like 10 tonnes of TNT being set off in the chamber.

So, with that little gem of info, does anyone have any doubts over the viability of tokamaks??.... nah! should be fine!

[Breakable]

So regarding tokamaks what are the breakthroughs that are required?
Do we need a 10T tnt resistant chamber?
Superconducting magnets does not seem to be a problem, but will they provide the required magnetic field? I heard superconductors stop working under some conditions, isn't high magnetic field one of them?

[Breakable]

PS:I dont think it is important what option does the reality represent, if the fusion power is possible or not at all, I just would like to know the favorites in the race.
PSPS:Fusion power is of course possible

[Breakable]

Some information from focus fusion:
1)The achievement of a pinch - done, confirmed?
2)At 25kV: Produce 1 MA, determine optiumum gas pressure
3)The theory that adding a small axial magnetic field, and thus a small amount of angular momentum, to the plasma will greatly increase the size of the plasmoids and thus the efficiency of energy transfer into the plasmoid.
4)Move to 45kV, 2MA, with Deuterium
5)Confirm Texas results ???, with better instruments
6)Heavier Gases: D + He + N, and shorter electrodes
7)The sixth goal is to confirm LPP’s theory that heavier gases will lead to higher compression and to thereby achieve gigagauss field.
8)pB11
9)Net energy with pB11.

http://focusfusion.org/index.php/site/a ... _timeline/

Anyone cares to speculate on the probabilities?

[D Tibbets]

One example of a usefull fusion powr plant that I think is generably considered doable with current tecnology:

Fission triggered fusion in the ground. Detinate a hydrogen bomb deep underground. Pump water into the resultant hot cavity, collect the resultant steam to power turbines, repeat as needed.

It has been a political decision not to go there. I don't know the cost, but some mild concern about drinking radioactive ground water may have contributed.

Dan Tibbets

[D Tibbets]

Perhaps true for hydrogen (P-P) but I don't think anyone is considering trying to do that on Earth. A better example would be gravitationally confined D-D reactions, or even D-P reactions.

The thing is, if that were to happen as a dominant reaction then that star where that is happening would super-nova because it is the 'self-regulating' properties of a gravitationally confined fusion core that allows it to work - the hotter it gets, so it expands and the reaction rate drops off. Too much energy will lead to 'too hot' will lead to supernova. This is pretty much exactly what happens - these 'higher power' fusion fuels are hanging around doing essentially nothing at p+p stellar temps, but when the p fuel runs out, the star contracts, gets hotter, and these reactions kick off and the thing goes 'whhoooommfff'.....! ....

It would only go "whhoooommfff" if your reactor was equivalent to the Sun in mass. Think brown dwarf. Much smaller volume, much less gravity, mouch more energy density(with D-D). In order to provide for all of Earth's energy needs you would only need a deuterium powered brown dwarf reactor perhaps twice the diameter of the Earth!

Dan Tibbets

[Breakable]

... you would only need a deuterium powered brown dwarf reactor perhaps twice the diameter of the Earth!
Dan Tibbets

I guess this is ITER v2.0?

[chrismb]

... you would only need a deuterium powered brown dwarf reactor perhaps twice the diameter of the Earth!
Dan Tibbets

I guess this is ITER v2.0?

Nice response!! To the casual obseerver it does seem to be going that way! But ITER is about the size that a full system will be, the extrapolations indicate negative consequences with much bigger sizes.

Yes, indeed, there must be some gravitationally confined size that can burn DD, but as you come down in gravity you come down in density, reaction rate is density^2, you end up with similar sizes anyway.

[Breakable]

viewtopic.php?t=1584
chrismb cared enough to comment on most important technologies, unfortunately no-one cares to discuss...

[chrismb]

Well, to be fair, you're on a discussion forum for Polywell. I have different motivations to Polywell enthusiasts.