Talk-Polywell.org

I got access to this paper through my school's journal subscriptions:

Rostoker, Norman, Michl W. Binderbauer, and Hendrik J. Monkhorst. "Colliding beam fusion reactor." Science 278.n5342 (Nov 21, 1997): 1419(4). Academic OneFile. Gale. 1 Nov. 2007

They had an interesting point about using some kind of funnel to collect the alphas and run them into a magnetron, I think, that produces microwaves, and then convert the microwave radiation to electricity, with 90% expected efficiency. They called them Peniotron and Gyrotron converters. They also mentioned this Artemis reactor with a "traveling wave direct converter" that had 75% efficiency. So it looks like there may be a way around using direct electrostatic braking.

The conversion efficiency at 100s of Mw is not going to be 90% at the present state of technology.

It is hard to get into the 90% - 95% range with 30KHz. And we can use honking power diodes at that frequency.

Deceleration is probably the best idea for the first round of power producers.

Even if it makes the reactors 6 M across - that is small compared to steam plants with turbines or gas turbines of similar power.

MSimon wrote:Even if it makes the reactors 6 M across - that is small compared to steam plants with turbines or gas turbines of similar power.

Presumably a lot cheaper, too, yes? One of the big costs of a steam plant are those big, rotating, copper-filled (? correct me if I'm wrong) generators.

Scareduck,

Turbines (steam plant in general) are the cost drivers.

In a conventional nuke steam plant represents 80% of plant cost.

I don't think there is a simpler or significantly better way for energy conversion in a polywell, than electrostatic braking.
A big part of the conversion losses for that case are alphas hitting the MA-grid, and it seems unlikely that there is a method which can avoid that.

6 m across doesn't seem feasible to me.
If the polywell is 2 m radius, this only leaves a one meter gap over which a voltage of 1.5 MV would be applied (not considering the faraday cage and the electron sources which also should go somewhere in there).

Nebel says in this pdf that you can get a pretty high field strength, on the order of 100kV per cm, I think!

http://mr-fusion.hellblazer.com/pdfs/al ... nement.pdf

I was thinking 10 KV/cm as a design goal.

1 m = 1 MV. That might be too generous.

A lot will depend on the density outside the reaction area.

Yeah, that's pretty much an electric bomb waiting to go off!

As for inefficiency, the problem is that it bites both ways: not only do you not get that energy, but you will most likely have to struggle to get it out of your machine so it doesn't overheat (just like the situation with the magrid coils and the alphas).

It's nice for once that the simplest solution might just be the best!

^ I like simple solutions to complex problems. Occam's razor applied to engineering problems is a powerful tool.

Hi All--

I recently realized that I have no idea how electrostatic braking is going to generate a voltage. Bear with me, I'm sure I'm misunderstanding something here:

First, we have (at some fairly large radial distance from the center of the polywell) another big honking spherical anode. Presumably this anode is made out of some sort of metallic conductor. Because it's an anode, it's had some voltage applied to it that effectively sucks a lot of the electrons out of the metal, leaving in place a positively charged lattice of metal atoms.

Now, I fire an alpha particle radially out towards this big honking anode. Because of Coulomb's law, that alpha particle feels an ever-greater force at it comes closer and closer to the anode. Here's where I start to lose it: First, because the alpha particle is decelerating, it's generating a perpendicular B-field, right?

So, question #1: Isn't the generation of that B-field just dumping energy into free space?

And (related) question #2: Isn't that B-field ultimately going to generate synchotron radiation?

And question #3 (which is the real question): How does this lost energy get recovered?

Now, I'll assume that somebody's going to come up with satisfactory answers to all of these questions, (which will no doubt leave me feeling kinda stupid) and we're going to be left with the ever-increasing electrostatic force causing the direct conversion. Which is where I then get confused again:

Question #4: How does electrostatic force generate a current out of the anode? It's clearly not pushing the metallic atoms out to generate a current. That would merely generate a bunch of heat, right? So what's the mechanism?

And finally, question #5: Once we've decelerated the alphas to some very low energy, where do they go? And, once they're sent wherever they're going, why doesn't their removal reverse whatever voltage got generated?

As I said, I'm very confused. Help!

Electrostatic induction.

It is a particle accelerator in reverse.

BTW you induce a current. The voltage is fixed by the rate you draw off the current.

As far as radiation, I second that question! From my limited knowledge of physics, I've gleaned that accelerated charges produce radiation, and so I don't see why that wouldn't apply here. I wish I knew more!

Maybe it's just not a significant amount of loss: I think the acceleration that causes brehmstralung or snychotron (sp!?) radiation is probably much bigger, and there might be some scaling factors too. The limit on the efficiency of direct braking is said to be ~90%, so maybe the radiation is part of that. (I think the other part has to do with there being some KE left in the alphas when they hit the collector.)

As to current: The alphas are going to hit the anode, pick up electrons from it, be neutralized to He gas and leave the reactor. The 'soaking up' of electrons from the anode is what causes the current. But I really like what MSimon says, that it's just like a ion gun in reverse. That's the easiest way to think about it.

@ TheRadicalModerate

You have it mostly right. It is the acceleration (or deceleration) of particles that causes E&M radiation. So the alphas must radiate if we slow them down. But the frequencies are so low, the energy radiated is too small to worry about (other than over time we want to cool our outer shell). The main trick is to convert as much of the kinetic energy into electrical potential as possible, and the electrons trapped in the outer anode will do that. When the alphas hit the anode they will slow down enough to collect electrons and neutralize. then we need pumps to clear out the alphas. Since the vacuum pumps are connected to the outer walls anyway, and the high energy alphas coming from the core fusion will knock the lower energy neutralized alphas out to the walls, we have a pretty good pumping solution for cleaning out the system.

The electrons get brought into the anode as the alphas push on the ions in the metal. The attempt to prevent them from going there is the anode potential, but the energy in the alphas brings thems in (it's the accelerator in reverse Simon is talking about). The process of converting kinetic energy into potential energy is really all that is going on, it's just being done with charged particles.

Hope that helps!