Harnessing Ion Energy

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

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isadharvey
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Joined: Wed Jun 06, 2012 3:38 am

Harnessing Ion Energy

Post by isadharvey »

I've seen it mentioned that with the emission of charged particles, the energy is already in the form of electricity and can be harnessed directly with near 100% efficiency.

Assuming a uniform radiation of alpha particles from the centre of a device, how exactly would the energy be turned into the usual electron-based electricity? I've been looking for an answer and asking some physics students for some time now, and haven't got a decent answer yet.

ladajo
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Post by ladajo »

Try looking up "Venetian Blind Collector"

The Alphas make essentially a 2.3Million Volt positive potential, this is what makes the electrons feel the need for speed.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

KitemanSA
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Post by KitemanSA »

The unstated assumption here is that pB&J will work. For DD or DT, most energy comes off as n+p or 2n so those would need a thermal cycle to extract the energy. But given pB&J, the alphas actually come off with two sets of energy, the first controlled by the 12C*(,α)8Be and the second by the 8Be fission to 2α. The first will have a fairly unique energy and the seond two will come out with a span of energies that is the sharing of the Be=2α fission energy plus the portion of the energy the Be got from the first reaction.

I found my copy of the "venetian blind" paper at:
http://www.askmar.com/Fusion.html

isadharvey
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Post by isadharvey »

I've read the article, but I'm not sure I completely understand it. From what I can see it seems mostly a method to soft-land the charged particles onto a surface to draw out electrons, making the current essentially reverse ionization. How is the kinetic energy of the alpha particles harnessed apart from making heat? If it is simply reverse ionization, how can it be possible to make energy in total when ionization is required in the first place to perform the fusion?

KitemanSA
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Post by KitemanSA »

The ion climbs a ~2MV potential across the vacuum chamber and the electrons travel the same 2MV path thru the load attached across the terminals (ground cage and chamber wall. That current (electron flow) and voltage provide the power.

There is no (or very little) heat because the ion looses its kinetic energy while climbing the potential.
Last edited by KitemanSA on Mon Jun 18, 2012 11:33 pm, edited 1 time in total.

hanelyp
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Post by hanelyp »

The simplest direct conversion method proposed for the polywell is a Van de Graaff accelerator run in reverse. Efficiency of this is sensitive to the energy distribution of the fusion products. The venetian blind style device I understand to be a more advanced device that sorts the alphas by energy.

D Tibbets
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Post by D Tibbets »

isadharvey wrote:I've read the article, but I'm not sure I completely understand it. From what I can see it seems mostly a method to soft-land the charged particles onto a surface to draw out electrons, making the current essentially reverse ionization. How is the kinetic energy of the alpha particles harnessed apart from making heat? If it is simply reverse ionization, how can it be possible to make energy in total when ionization is required in the first place to perform the fusion?
Actually , there are two electron drawing stages. The high energy alphas flying past negatively charged plates gives up part of their KE. This essentially creates a potential gradient in the plates that draws more electrons from ground and imparts high KE or voltage to them. This is a high voltage generator. Once slowed down the alphas hit a wall, and depending on design electrons drawing is at such low voltage that the thermal processes (ion hitting the wall) dominates. This heat needs to be extracted- through coolent flow. Depending on the total efficiency of the energy conversion , this left over KE which is converted mostly into thermal energy, after extraction may be used to spin a turbine, or just sent directly to a cooling tower. The final solution is a compromise between efficiencies and thermal loading engineering, not to mention spalling concerns.
The magrid is a direct conversion device for electrons , with the exception that a grounding plate (grid) is not provided for the decelerated electrons so they reverse course and are reaccelerated back into the magrid volume. Even here though, there needs to be a grounding plate for the up scattered electrons to prevent their accumulation outside the magrid or looping back into the magrid volume at undesirable higher energy. The magrid is a single stage electron direct energy converter. for escaping electrons. If the grounding plates were a little closer, the escaping electrons would not recirculate, but ground on the plates, and the direct conversion would recover the energy. And this could be used to generate new high energy electrons. The problem is that the efficiency of this is probably well below recirculation efficiency , which is perhaps 90% or higher.
Add to this the complexity of segregating the electrons from the ions (mostly by momentum differences). The electrons can be diverted to a grounded plate deep within the converter stack, while ions are diverted only a little bit, and thus can continue past to additional plates and be decelerated and diverted without now absent electrons being accelerated.

Dan Tibbets
To error is human... and I'm very human.

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