Are JET and ITER really any LESS stable than the SUN??

[Dan Tibbets]

Comparing Tokamak instability to the sun would best be compared to solar flares- Coronal mass ejections, not the red giant stage. The red giant stage is a fuel issue, the aviable hydrogen is used up, the core cannot support itself against gravity and it is compressed-and heated by the compression untill the helium ash starts to burn. As the core is now smaller, but much hotter it heats the overlieing gas and like any gas as it is heated it expands - into the red giant size. Also, a white dwarf is a dead star. It has burned all the light elements it can- up to ~ iron ( actually most only have enough mass to fuse up to carbon or posibly oxygen. The star in its red giant stage has ejected most of the outer gas envelope and just the core is left. When a white dwarf star is young this exposed core surface is at ~ 100,000 degrees C and emits copius amounts of UV light - which is what energies the planetary nebula that formed during the red giant stage. The white dwarf then cools passively ( black body radiation). Unless the white dwarf has a close companion star that it can steal matter from -leading to novas or a type of supernova, the white dwarf will gradually cool and dim over billions of years till it is just a lump of 'coal'.
Actually, the Sun is fairly stable as stars go (fortunately for us). Instead of the Sun as an an example for instability, red dwarfs are better. Some tend to be much more unstable. Some can change in brightness by several hundred fold within days, or even hours .
http://en.wikipedia.org/wiki/Flare_star

And the big boys like Eta Carni can occasionally burp and eject multiple solar masses worth of matter within days.


Dan Tibbets

[Dustinit]

Its interesting that you say its a lump of coal,
I recall that once it was seriously considered early on that it was coal that fuelled
the sun but I think it was discarded because it wouldnt burn for long enough.
Dustin

[Chris Bradley]

Sure. All agreed.

I'll go further than that to look at the differences:

The sun versus tokamak;
different volume, by 27 orders of magnitude,
different pressure, by 14 orders of magnitude, (equivalent to 28 orders of magnitude rate reactions)
different temperature, by only one order of magnitude, (but reaction rate is a negative exponential function, could we call that e^-10 = 5 orders of magnitude?)
different fuel, giving a different fusion probability 25 orders of magnitude difference,
different shape,
different containment mechanism,

..have I missed anything..?

..not a tiniest scrap of similarity. Complete nonsense to draw any similarities between a tokamak and a star (as so often poetically described in the public domain).

(In fact, is there ANY unique distinguishing feature that is common to the two processes that is not common between some other two processes??)

We're looking at a 'sum total' of 85 orders of magnitude difference - some plus, some minus.

All the more odd, then, that relative overall 'burntime' between the two can be predicted using these simple assumptions of instability within just one order of magnitude!!??

Maybe it's just co-incidence, of course, but co-incidence isn't the first thing I think about when the maths supports an argument. Instead I start wondering what else to look for that might show it was just co-incidence, before dismissing it.

best regards,

Chris MB.

[Richard Hull]

The Sun and the Tokamak both do fusion via a thermal process of heating the fuel. (maxwellian devices) Just about the only similarity.

Richard Hull

[Chris Bradley]

I'd suggest even those two points are arguable.

The sun heats itself by its own reaction, initiated by a one-time gravitational contraction and sustained by being well-insulated.

The Tokamak requires a continuous energy input to maintain the heat and looses all the energy it produces in neutrons that escape the plasma.

So one *is* a thermal process, the other *is acted on by* thermal processes.

The second point is a bit more obscure - I note recent published research that shows as temperature increases to earthbound tokamak levels, the thermal distribution drifts away from Maxwellian into an inverse 8th power function due to quantum effects.

[Mike Beauford]

That's interesting about the 8th power. I think I recall Dr. Bussard said something similar I thought when he was describing how his pollywell would size vs power.

[Chris Bradley]

I couldn't say if that is a co-incidence or not! The derivation of the inverse 8th power momentum distribution is the work of Galitskii and Yakimets. With names like that, I expect it is easy to search for them (!), if such details of plasma dynamics is of interest. I don't know much about this, only that I came across it whilst researching non-maxwellian distributions.

[Dan Tibbets]

Indeed there is little similarity except the fusion reactions themselfs (hopefully). But, in terms of the plasmas and their reactions, the studies of low to high mass stars, neutron stars, black holes , etc might give insights into the interactions of plasmas, and magnetic fields on the Earth (and visa versa). And, while still driven by gravity, Novas are nuclear detonations on the surfaces of white dwarf stars that have accumulated enough hydrogen from a close companion.
http://en.wikipedia.org/wiki/Nova
How the star accumulates enough hydrogen and compresses/heats it to ignition conditions without first ejecting the hydrogen in a powerful solar wind is interesting. From an idiots perspective I can speculate on various gravity gradiants, companion star feed rates, sound waves/ shock wave effects, and magnetic effects that might apply. And to drift further off topic, if the white dwarf star accumulates enough hydrogen from a companion star to blow off a portion of it in a Nova periodically, how can it go past that point to where enough mass is accumulated to trigger the fusion of the entire core's content of carbon/oxygen into iron - type 1a Supernova?

Dan Tibbbets

[Dissident]

I'm more interested how Jet aircrafts can be replaced with plasma saucers - something like the "Lightcraft" of NASA. When??

[Carl Willis]

Lubomir, you're in the wrong place to carry on like this. You need to keep your additions topical (i.e. the science of nuclear fusion) or you'll find your postings shuffled off to the troll repository.

Thank you--in advance--for playing by the rules.