Questions around the copper Anode

[Allan Brewer]

I would like to understand more, so I have a few questions about the anode on the FF-1:

(a) There has been mention (re measuring the power of the pinches) of erosion of the copper anode by the electron beam from the pinch. Would the vapourised (apologies for the English spellings!) copper get involved in the nuclear reaction – i.e. would it mop up protons? – perhaps not in single pinches but if the machine is cycling so that the copper vapour might still be present at the beginnining of the next pinch??
(b) Why, if the positively-charged ion beam is passed through a coil to transform its energy into electricity, is that not also done for the electron beam from the pinch i.e. through a hole on the anode??
(c) Will the production anode still be copper or beryllium like the cathode??

[Lerner]

Right now the copper at the top of the hole in the anode is too far away to get into the plasmoid, we think. It deposits all over the inside of the vacuum chamber and is certainly not in vapor form at the time of the next shot.
We hope that when the DPF is optimized almost all of the e-beam energy will be deposited in the plasmoid, leaving very little in the exiting beam.
Beryllium will be used in the generator and possibly in the experimental device if erosion by x-rays gets too severe.

[psupine]

I’m still trying to understand some of the subtleties too (I bet we all are!), so please excuse me if this question is so bad that it isn’t even wrong …

Doesn’t conservation of momentum require a significant e-beam to balance the ion-beam from which we hope to extract significant energy? So if optimality has the e-beam energy reduced as much as possible, I’d have thought that the ion-beam is similarly down to nothing or else the plasmoid shoots sideways (or rather in FuFu, up).

I’m sure someone can set me straight. I hope to get there eventually.
Thanks

[Lerner]

It is very difficult for the electrons to balance the momentum of the ions which are thousands of times heavier. Two things can absorb the momentum of the ion beam–the motion of the plasmoid, or the magnetic field that the plasmoid is tied to. It is probably mostly the latter, since otherwise the plasmoid would smash into the anode before the pulse ended.

[psupine]

OK, so it’s partly that the plasmoid itself is considerably more massive than the electron stream, but are you also saying that there is some residual magnetic field that the plasmoid pushes against, ie some magnetic lines of flux still attached to the electrodes?

I’m still confused though; the charge of the electron beam has to balance the charge in the ion beam. I had imagined the electrons firing back through a hole in centre electrode to provide a negative charge path back to the outer electrodes. Rather, is the goal here to hold the electrons close to stationary trapped in the plasmoid so that the alpha particles go zooming off even faster towards the “decellerator coil”.

[Lerner]

The electrons still leave–it’s a question of how fast they are traveling. If 99% of the e-beam energy is deposited in the plasmoid (which would be great) you still have each electron having 30 keV of energy, so they will zip right along–in fact they will travel nearly as fast as the ions.

[JimmyT]

I was wondering something similar on a stellar scale. Is there any evidence that the Herbic-Harrow objects are being accelerated. (probably can’t tell, too far away, acceleration too slight, etc.)

Still, maybe over long time spans……

[Aeronaut]

The vacuum chamber and cathodes are at negative (ground) potential. The angular momentum determines plasmoid diameter by countering the collapsing magnetic field, if I understand it correctly. This is how the plasmoid and field are connected. Thanx, I’d missed the recoil implications.

[jamesr]

Aeronaut wrote: This is how the plasmoid and field are connected.

As far I was concerned the plasmoid is the field by definition. ie. when the magnetic field lines break and reconnect to form an closed structure, that is called a plasmoid.

This can only happen in the presence of a plasma with a temperature and pressure such that the collisional effects (electrical resistivity) enable transfer of energy from the ions & electrons to/from the field, and so change the topology of the magnetic field.

(PS. it is refreshing to have a thread that is slightly more on-topic than some of the other recent discussions)

[psupine]

Lerner wrote: Two things can absorb the momentum of the ion beam–the motion of the plasmoid, or the magnetic field that the plasmoid is tied to. It is probably mostly the latter, since otherwise the plasmoid would smash into the anode before the pulse ended.

jamesr wrote: As far I was concerned the plasmoid is the field by definition. ie. when the magnetic field lines break and reconnect to form an closed structure, that is called a plasmoid.

1) Is there any evidence that the the plasmoid does smash into the anode? Do we know how much it will move before total collapse?

2) What happens to the e-beam? Does it go through a hole in the anode for the charge to be re-cycled into the following shot, or is the energy so small that it isn’t worth the trouble and it simply shorts out into the positively charged anode?

[Aeronaut]

In a perfect scenario, 100% of the ebeam would be absorbed by the plasmoid. The fraction that is absorbed heats the plasmoid, increasing the rate of fusion events, and thus the energy produced that machine cycle. The unabsorbed ebeam fraction expends it’s energy as a heat pulse on the anode, which vaporizes a certain amount that doesn’t hurt a research reactor significantly, but would be unacceptable in a working reactor at even 330 hz.

[benf]

I envision a control knob like on my old train set transformer. Turn up the juice for higher output and faster speed. Is that all there is to do to reach unity now? That would be lucky…What are the mechanisms of control to optimize the formation of the plasmoid aside from gas pressure, positioning of the cathodes to the anode and increasing current? I’m wondering about how the filaments interact with the gas. Apart from increased pressure of the gas increasing density. The density is homogeneous, would there be any benefit to imparting motion to the gas medium as you do with the angular momentum to the magnetic field? A swirling vortex of gas would mimic galaxy/solar system formation, would that apply to a DPF? The circulation also might aid in cooling, or would this make everything unstable?

[Allan Brewer]

Aeronaut wrote: In a perfect scenario, 100% of the ebeam would be absorbed by the plasmoid. The fraction that is absorbed heats the plasmoid, increasing the rate of fusion events, and thus the energy produced that machine cycle. The unabsorbed ebeam fraction expends it’s energy as a heat pulse on the anode, which vaporizes a certain amount that doesn’t hurt a research reactor significantly, but would be unacceptable in a working reactor at even 330 hz.

So how will the unabsorbed ebeam fraction be allowed to expend it’s energy in the working reactor at 330Hz?? Eric seemed to imply in an earlier reply that the research machine would get a Beryllium Anode if the copper vapourisation got too heavy – does that mean Beryllium would react to the ebeam differently, or is that just a convenient replacement??

[jamesr]

As Aeronaut pointed out – the e-beam hits the anode and vaporizes a small are of a creating a pit ~18microns deep per pinch according to this report. Also it deposits its charge into the circuit, but this is not significant electrically.

Beryillium’s boiling point of 2742 K is not that different from copper’s at 2840 K, but since it is a much lighter element (& so each atom has less electrons) I would expect the electrons in the beam to penetrate further into it as they slow down, depositing their energy over a greater overall volume of material. This may mean the energy deposited in one spot is not enough for it to vaporize, or conversely it could mean an even larger pit is formed, only experimental testing (or very sophisticated modeling) will give us the answer.

[psupine]

As I understand it, one of the techniques used in electron tubes (aka valves) to reduce electrode erosion is to a maintain a negative potential on the “target” electrode. This decelerates the free electrons (that had been accelerated by the grid potential) so that most of the energy has been taken out of them and the electrons impact the plate at low energy. This is a bit like a lunar lander game played out on a very small scale.

If the same situation applies here, then allowing the residual e-beam to contact the +ve anode is the actually making the electrode erosion problem worse, because the electrons are accelerated towards the +ve anode. (Maybe it’s no longer positive after the discharge that formed the plasmoid, but in any case the following should still apply)

Couldn’t we instead have a hole up the middle of the anode and a negative electrode (insulated from the anode) whose task it is to slow the electrons and allow the e-beam to touch with the minimum erosion? The accumulated negative charge would be bled back into the power supply, even if that energy contribution was small.

The unanswered question I’m left with is what is this electrode negative with respect to? The plasmoid is going to be sitting in an electric field at some potential, but I don’t know what that is.

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