Talk-Polywell.org

If I'm not getting this wrong, electrons are confined by /b/ fields at the center region. Boron ions will be super accelerated from the outside toward the center, they will then smash into the hydrogen ions that are already at the center...? How are the hydrogen ions being held at the center as well?

If I understand correctly, the amount of acceleration due to the electric force would not be high enough to fuse boron/boron collisions, since the hydrogen ions are not really moving, or they are moving slowly, we dont have to worry about those, electrons on the other hand are moving too slow and are too small to worry about boron ion/electron collisions, they wont be able to pick them up and neutralize the boron ions anyways.

The protons are slamming into the center too. They all have the same voltage (potential energy) so the mass determines the velocity. The boron ions will be moving a lot slower (like sqrt(11) times slower) than the protons.

The electrons won't just be hanging around either. But in the center, they will be at their slowest while near the MaGrid they will be fastest. Ideally motion will be mostly radial, but reality never works that way.

As I understand it, p-p fusion is fairly difficult, so we still don't have to worry about those. But I just started here, I wouldn't take my word for it!

drmike wrote:The protons are slamming into the center too. They all have the same voltage (potential energy) so the mass determines the velocity. The boron ions will be moving a lot slower (like sqrt(11) times slower) than the protons.

I thought that due to Boron ion's +5 charge, its PE would be 5 times as much in the same electric field, vs the proton?

JohnP wrote:

drmike wrote:The protons are slamming into the center too. They all have the same voltage (potential energy) so the mass determines the velocity. The boron ions will be moving a lot slower (like sqrt(11) times slower) than the protons.

I thought that due to Boron ion's +5 charge, its PE would be 5 times as much in the same electric field, vs the proton?

Yeah. So it would be sqrt(5/11). Or about .67 proton velocity.

E~=mv^2 so 5=11V^2 - 5/11 = V^2 - sqrt (5/11) = V - V= .67

JohnSmith wrote:As I understand it, p-p fusion is fairly difficult, so we still don't have to worry about those. But I just started here, I wouldn't take my word for it!

P-P fusion is harder than P-B fusion? Why? Explain please.

Well, my thinking was, why on earth do we use D-T instead of p-p if p-p actually easier? Then I tried to read up on it, and it gets kind of complicated.
Best guess, since there's no neutrons, the strong nuclear force is half of Deuterium's. That would raise the energy quite a bit, I think. No idea if that makes it harder than p-B, but I don't think I've ever heard about pBj producing Deuterium.

JohnSmith wrote::? Well, my thinking was, why on earth do we use D-T instead of p-p if p-p actually easier? Then I tried to read up on it, and it gets kind of complicated.
Best guess, since there's no neutrons, the strong nuclear force is half of Deuterium's. That would raise the energy quite a bit, I think. No idea if that makes it harder than p-B, but I don't think I've ever heard about pBj producing Deuterium.

The ratio of the strong force to charge is the important deal. More neutrons per proton is good. H= 0/1 D=1/1 T=2/1.

D-T has the lowest energy of activation.

D-D is the most abundant and a little harder to ignite.

P-B11 has the lowest neutron output but is pretty hard to ignite.

so are P-P reactions harder to achieve than P-B11? Cus if not, we may have to worry about those P-P reactions happening without us intending it to happen.

Robthebob wrote:so are P-P reactions harder to achieve than P-B11? Cus if not, we may have to worry about those P-P reactions happening without us intending it to happen.

Yes. It is much harder due to the low fusion cross section of p-p.

In fact no one knows the actual cross section (IIRC) there is just an estimate of the upper bounds.

Robthebob wrote:so are P-P reactions harder to achieve than P-B11? Cus if not, we may have to worry about those P-P reactions happening without us intending it to happen.

According to wikipedia, the p-p reaction involves the weak nuclear force, while every other reaction we've been considering (D-D, D-T, p-B11) involves the strong force only. The weak nuclear force is, well, weak, and reactions involving the weak force typically have very small cross sections, and so are low probability events.

I get the impression that it's the limiting reaction in the p-p chain reaction because the cross-section is so low.

MSimon, if it's the neutron/charge ratio that tells you how likely fusion is, shouldn't T-T be a substantial side reaction in D-T reactors?

For that matter, wouldn't T-T be a very attractive fuel from a physics perspective? I know that T is rare enough that it's not economical, but I could imagine it being used in experimental reactors.
I've never heard of it, though. Am I missing something?

JohnSmith wrote:MSimon, if it's the neutron/charge ratio that tells you how likely fusion is, shouldn't T-T be a substantial side reaction in D-T reactors?

Yes.

Have a look at the wiki on fusion which was pretty good lat time I looked.

Hum. I've given it a once over, and I'll go thorough it at depth after monday. Exams and all that fun stuff are keeping me a bit busy, I've got to fill my head with the wonders of molecular biology rather than fusion.
I did notice, though that the Tritium article says that D-T has the largest cross section of all the fusion materials.