Alpha conversion to electricity

[mitakeet]

Hello everyone!

I am sure my question has been answered, but clearly I am not using the correct key words to locate it. I have read over and over again about the 90+% capture efficiency of the alpha particles into electricity, but can’t for the life of me find anywhere that gives a detailed explanation that doesn’t assume a PhD in high energy physics. I am hoping the people here can give me some pointers to find some information. I have searched on ‘alpha-voltaics’ and ‘alpha particle batteries’ and found a lot of interesting stuff, but except for a couple of rare experimental exceptions, the efficiencies are all reported in the very low end.

Thanks!

[zapkitty]

1. Alpha particles are helium nuclei.

2. As the He nuclei are sans electrons they carry a charge.

3. An FF unit happens to eject a stream of these charged particles at high velocity along the axis of the core with each pulse.

4. If one wraps a coil around the path these particles take it is basic induction physics to charge the coil and extract work from these fast-moving particles. The slowed particles then hook up with some electrons and become the helium that is the “exhaust” of an FF unit.

As with the x-ray photovoltaics this is known physics, no speculation as to possibility required, but there’s never been any need outside of fusion physics to research the best methods of building these things… and with the tokamaks dominating fusion research funding there was almost no money to check it all out regardless.

The closest practical research along these lines was “alpha batteries” which generally rely on plutonium radiating the alphas in an omnidirectional spray. and thus are not applicable to an FF unit. However you will find that the Polywell (another aneutronic fusion contender) and its “venetian blinds” alpha collectors are closer to the alpha battery designs than anything in an FF unit.

Does this help?

[mitakeet]

Hello Zap!

I understand the whole thing about alphas (I worked with radiation extensively back in college), just not how to capture the energy from the things. I can sort of visualize the coil you are talking about, but if you know any detailed drawings that would be very helpful. I have read about the ‘venetian blind’ bit, but just words (Googling finds way too much noise to be useful), no schematics or anything. Your explanation that the idea really isn’t mainstream does help me understand my lack of success in finding information. I have been reading up on the alpha battery concept, the use of semiconductors to capture the energy (largely unsuccessful because the energy of the alpha destroys the crystal structure of the semiconductor) as well as the idea of turning the alpha’s energy into photons (rather than electrons) and then capturing the energy via photovoltaics. I guess having read so may blithe assertions that the alpha’s energy could be captured at 90+% efficiency I assumed that was based on people having actually done it economically as opposed to theoretically.

Thanks for your info!

[Francisl]

The alpha particles are released in pulses. This creates a pulsating magnetic field that can be captured in transformer coils. Look for references to this specialized coil called a rogowski coil

[tcg]

The basic theoretical support goes back to Maxwell’s theories of electro-magnetism. A charged particle moving through a coil of wire will induce an electric current, loosing some of its kinetic energy. Such a device is basically a particle accelerator operating in reverse. Perhaps the statement of 90% efficiency is based on the performance of such accelerators, which are highly refined instruments. It may be that the hard data is lacking yet because such an abundant and tightly colimated stream of alpha particles traveling at such a high velocity has been a rare item. As an electrician, I am confident that to develop this part of a future FF generator would present surmountable technical problems.

[mitakeet]

Thanks for the feedback!

I haven’t been able to find much on the Rogowski coil, unfortunately. I have found this patent, though:

“Apparatus for direct conversion of radioactive decay energy to electrical energy” (4,835,433)

but haven’t figured out yet how to get Firefox to install the image viewer. I found some smaller images elsewhere on the ‘net (for instance http://www.scribd.com/doc/8929973/Nuclear-Battery on page 9), but in any case, I would wonder how economically practical it is as it looks very complicated and thus expensive to build.

If anyone knows of something that is actually in-use to capture as electric energy the movement of the alpha particle please speak up, but I am getting the impression that, just like the promise of fusion energy, theoretically trivial often turns out to be extremely non-trivial in practice.

[zapkitty]

mitakeet wrote:
If anyone knows of something that is actually in-use to capture as electric energy the movement of the alpha particle please speak up, but I am getting the impression that, just like the promise of fusion energy, theoretically trivial often turns out to be extremely non-trivial in practice.

Well, aside from the dual non sequitur of calling transformer mechanics “non-mainstream” and the assumption that because it’s not a standard power generation mechanism it must somehow be unusually difficult, your premise would also require ignoring every instance where someone has used a magnetic spectrometer or other electromagnetic instrument to measure alpha particle properties.

[benf]

mitakeet here’s a link to a forum thread that shows illustrations of the rogowski coil that have been kicked around (click below):

Thread…

[mitakeet]

Benf, thanks for the link!

[BSFusion]

zapkitty wrote: 1. Alpha particles are helium nuclei.

2. As the He nuclei are sans electrons they carry a charge.

3. An FF unit happens to eject a stream of these charged particles at high velocity along the axis of the core with each pulse.

4. If one wraps a coil around the path these particles take it is basic induction physics to charge the coil and extract work from these fast-moving particles. The slowed particles then hook up with some electrons and become the helium that is the “exhaust” of an FF unit.

As with the x-ray photovoltaics this is known physics, no speculation as to possibility required, but there’s never been any need outside of fusion physics to research the best methods of building these things… and with the tokamaks dominating fusion research funding there was almost no money to check it all out regardless.

The closest practical research along these lines was “alpha batteries” which generally rely on plutonium radiating the alphas in an omnidirectional spray. and thus are not applicable to an FF unit. However you will find that the Polywell (another aneutronic fusion contender) and its “venetian blinds” alpha collectors are closer to the alpha battery designs than anything in an FF unit.

Does this help?

I have a stupid question: After C12* fissions into three alpha particles, what happens to the electrons? Its been said that the alpha particles all fly off in the same direction, is there some reason that the electrons do not follow after them? And, if the electrons catch them, will that neutralize the charge and make the energy recovery coil ineffective?

[Henning]

Electrons fly off in the other direction than alpha particles, because of the magnetic field (right-hand rule).

[jamesr]

Henning wrote: Electrons fly off in the other direction than alpha particles, because of the magnetic field (right-hand rule).

It’s not the magnetic field directly. As far as I understand it, it is when the concentrated magnetic field created by the pinch collapses, the rapid change in magnetic field creates an electric field by Faraday’s law dB/dt=-curl(E).

The symmetry of the highly curved magnetic field creates the electric field such that it is directed along the axis of the DPF, accelerating the ions in a cone of around 6degrees away from the anode and the electrons in the opposite direction. However, the electrons have much lower inertia and as they start to be accelerated scatter off ions transferring some of their energy to them, before starting to accelerate down the E-field again. So rather than being able to build up into a coherent beam, a large fraction of the electrons don’t make it out of the plasmoid. Some do make it out and are accelerated enough to blast a little pit in the anode.

After the collapse of the field the plasma will of course react to re-establish quasi-neutrality where any imbalance has built up, but this is on a longer timescale.

It is also worth reiterating the formation of the beam of ions is nothing to do with the fusion or alpha particle directions. Ion beams are created in all DPF’s that manage to form a strong pinch, even with un-reactive gasses. Any fusion alphas (or other charged products in the case of other reactions), which although initially moving much faster than the rest of the ions in the plasma are still confined by the magnetic field of the plasmoid. It will take them roughly 20 collisions to dump most of that kinetic energy and thermalise with the rest of the plasma (heating it in the process) but this occurs on the pico-second timescale rather than the tens of nanosecond lifetime of the plasmoid.

[vansig]

basic rules of the Rogowski coil are: the windings of the coil are arranged such that current in the coil will flow parallel to the direction of the alpha particle pulse, and the magnetic fields consequently arrange themselves to oppose this current, thus making it a particle decelerator. (just like a particle accelerator, only in reverse).

[yempski]

vansig wrote: thus making it a particle decelerator. (just like a particle accelerator, only in reverse).

But particle accelerators are very inefficient… I guess this is a problem for later

Here’s an interesting patent the topic

http://www.google.com/patents/EP2297841A2?cl=en

[vansig]

rogowski coil efficiency is expected to be similar to that attained by large power transformers, and those are routinely around 99%. the rogowski coil ought to be > 80%.

[Author]

Posts