Does the Gyroradius of an Alpha fit in a cusp?

Discuss how polywell fusion works; share theoretical questions and answers.

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TallDave
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Post by TallDave »

DTibbets wrote:I'm thinking that the balance has feedback, so long as there is a modest excess elecron current, the cusps will open up slightly(hopefully slightly) as Beta=1 es exceeded, and the excess electrons will spill out .


Maybe. I guess I've always assumed from Bussard's "blowout" terminology that when you broke beta = 1, the WB popped like a balloon -- that is to say, you can't just reduce the flow at that point and squeeze the cusps closed again, you have to start over. But I don't really know for sure. Ah, for a look at the WB-7/8 data...
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

happyjack27
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Post by happyjack27 »

TallDave wrote:
DTibbets wrote:I'm thinking that the balance has feedback, so long as there is a modest excess elecron current, the cusps will open up slightly(hopefully slightly) as Beta=1 es exceeded, and the excess electrons will spill out .


Maybe. I guess I've always assumed from Bussard's "blowout" terminology that when you broke beta = 1, the WB popped like a balloon -- that is to say, you can't just reduce the flow at that point and squeeze the cusps closed again, you have to start over. But I don't really know for sure. Ah, for a look at the WB-7/8 data...
from my sims it looked like it "popped" if the plasma pressure was too great for the magnetic pressure, i.e. b>1. though increasing the magnetic field would squeeze it back in place pretty quickly.

it makes sense to me, too, from a nonlinear dynamics perspective: the "cusps" are essentially a combination of a stable and unstable manifold, and when you squeeze them smaller by approaching b=1 from the "left", you're squeezing those manifolds tighter together, and then at b=1 you reach a bifurcation where the stable and unstable manifolds annihilate each other resulting in a "catastrophe" - that is, where once there was a stable manifold, now there isn't, and the nearest stable manifold is quite a ways away. i might not have all of that exactly right, but i think that's the generaly principle that happens when you exceed b=1. so really you want to keep it just barely under b=1 because b=1 is actually a bifurcation point.

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