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There is a quote and citation on the "Antimatter" page of the obvious encyclopedic site (https://en.wikipedia.org/wiki/Antimatter), saying that positrons could be produced (in the future) at a rate of $250 million per 10 milligrams. Unfortunately, the author of that quote made it in 2006. Yet there is also a growing possibility of harvesting antimatter in the radiation belts, solar wind, or even lightning bolts.

This leads me to consider: If the production (or harvesting) of antimatter becomes practical, is it theoretically possible to have an antimatter electric power supply?

My idea of antimatter power goes like this. Positrons are contained in a vacuum chamber, probably with a magnetic field. Electrons are somehow shot into the chamber, colliding with the blob of positrons. This produces 2 gamma rays. The vacuum chamber is surrounded by solar panels, tuned to receive gamma ray frequencies instead of visible light, and thus converts the gamma rays into DC electric power.

For the sake of concreteness, let me ask 4 questions revolving around the engineering problems:

(1) Is it possible to build efficient solar panels tuned to gamma ray frequencies? They would also need a decent lifetime.

(2) How exactly would electrons be accelerated into the region containing the positrons? My intuition says that if a magnetic field is containing them, then an electron would have a hard time penetrating that field.

(3) Can we get enough power from this to self-sustain the magnetic containment field, as well as the electron accelerator, while still having a decent amount of leftover power to spare?

(4) Are electrons and positrons the best choice of matter-antimatter? From what i've read, it seems the simplest choice of annihilation---they produce just 2 gamma rays at low velocities---but perhaps other kinds of antimatter are easier to contain?

In case your wondering, i'm not trying to make a form of free/cheap power. I just think it would be great if we could replace nuclear reactors, both the plants and the naval drives, with something that has few moving parts with even better energy density. To me, that would be worth a somewhat bigger price than nuclear is today. It would also be nice if space stations and space ships were not so limited in their power generation.

DrZ214
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  • "solar panels" and direct harvesting are hard. Bigger (but easier) is to thermally capture the energy, then drive a heat engine. Nasa has a design for a positron antimatter engine here: http://www.nasa.gov/exploration/home/antimatter_spaceship.html – BowlOfRed Sep 18 '14 at 17:01
  • The high production cost of antimatter is pretty much baked into reality. The occasional antimatter particle generated by cosmic rays is too rare to be useful, so no, there won't be any antimatter drives, bombs etc.. Not that they have any actual advantage over fusion or fission. If anything, annihilation is pretty much useless for many applications, because the radiation it predominantly generates is high energy gammas... which are a pain to deal with. – CuriousOne Sep 18 '14 at 17:03
  • There are no free floating positrons. They have been created as electron positron pairs at some point in their life line. Thus energy conservation says that you can never have "leftover power to spare" . The best you could have would be a technologically hard to create "battery", i.e. energy storage device. – anna v Sep 18 '14 at 17:46
  • @BowlOfRed Decent NASA concept, but instead of heating fuel for high Isp, it should also be possible to heat water to steam and drive an electric generator. Since antimatter has such high energy densities, would this be more efficient than nuclear reactors? – DrZ214 Sep 19 '14 at 12:31
  • @CuriousOne About high energy, u could place solar panels at the right distance. GR energy should fall off as an inverse square like any other EM radiation. So distance the panels so they receive GRs when they're low enough energy to absorb without melting anything. 1 concern is that positrons & electrons have the same charge, meaning they repel each other. You would have to throw them at really high speeds to ensure they collide. The higher kinetic energy means higher gamma ray energy, but it should be overcomeable with properly distanced solar panels via the inverse square law. – DrZ214 Sep 19 '14 at 12:32
  • @user1705043: I suggest you inform yourself about the actual physics before dreaming up wild constructs. At this point you don't even seem to know that electrons and positrons have opposite charge, are attractive and annihilate by forming a positronium intermediate state. – CuriousOne Sep 19 '14 at 18:26
  • Thanks for pointing out my mistake, but tbh it seems to make my wild construct even easier. Since they attract each other, no need for super high velocities that would require more input energy (and possibly create more than gamma rays from the collision). My greater point in my previous comment, which I should have made clearer, was that it's not so much high energy of a gamma ray that's the problem, but rather the frequency of the gamma ray. If a solar panel can be tuned to receive gamma ray frequencies, then any too-high-energy problem is overcomeable by properly distancing the panel. – DrZ214 Oct 02 '14 at 00:12
  • GR energy should fall off as an inverse square like any other EM radiation. The energy of photons does not "fall off with distance." The intensity of a divergent beam of photons that are emitted from a point-like source falls off as $1/r^2$, but the intensity of a beam is not the same thing as the energy of the individual photons. – Solomon Slow Aug 10 '15 at 20:14
  • @jameslarge Okay, then does individual photon energy fall as 1/r? Which I guess we would call inverse linear? Note: I'm not talking about kinetic energy, which would stay the same as a photon hurtles through empty space. I'm talking about the amplitude of the light wave. It's frequency would stay the same, but it's amplitude must decrease over time in some manner, or so I thought. – DrZ214 Aug 10 '15 at 20:30
  • No, the energy of photon does not "fall off with distance." The energy stays the same until the photon is destroyed by interacting with matter. – Solomon Slow Aug 10 '15 at 20:33

3 Answers3

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You can't build solar panels tuned to gamma ray frequencies. Gamma rays are too energetic-creating a hole/conductor pair only yields a few eV, while the Gamma ray is hundreds of keV. It would be better to absorb it as heat and turn the heat into electricity (though there are losses there)

Unfortunately, the number of positrons in the sources stated are very small. The radiation belts are electrons and the solar wind is electrons and protons. Even the lightning is talking about amounts that make radiation doses, not total energy. If you want positrons, you have to make them from electricity, not the other way around.

Ross Millikan
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    +1, It should be also noted that if someone is discussing antimatter as a power supply (e.g. as the source cited in the OP) it is only in the sense of a very light and compact fuel which actually takes a lot of energy to produce. It could be a very practical means of storing energy, but not a conceivable means of harnessing energy (as you already state). – Void Sep 18 '14 at 17:34
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  1. Positrons have a positive charge and electrons have a negative charge. They would attract each other. Getting them to together is not a problem. You would not have to fire them into a cloud of positrons, as they would just be attracted in.
  2. They circulate in opposite directions in a magnetic field. So, containing them is also not a problem.
  3. The only thing stopping a functioning antimatter power generator, is our ability to produce positrons efficiently. All the other problems are easy fixed.
  4. One way to produce positrons efficiently is to use a positron breeder process. This process takes some of the gamma rays produced, and turns them back into positrons,and feeds them back into the reactor chamber. In just how to do this efficiently, would be the subject of some recent research.
Rin Minase
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Paul Lillington
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    It looks like #2 and #3 answer DrZ's #2 & #3 (or are at least related to those two), but your #1 and #4 don't seem to answer questions #1 & #4 listed. – Kyle Kanos Aug 10 '15 at 20:27
  • By interest in this answer. I have found the latest update about positron generator in april 2016 http://www.msnbc.msn.com/id/27998860/ – Thaina Mar 13 '17 at 03:20
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Anti-matter could potentially have a practical use as high energy-density fuel (or catalyst) for starships. The reason is being the fuel with the highest energy density possible. But the biggest limitation, even beyond the limited production, is the inability to store significant quantities of the substance safely. You could create magnetic containers, but with existing superconductors the mass of the container would exceed the mass of fuel by several orders of magnitude, making its prospect performance much worse that fusion rockets. If you add to the risk of complete destruction at the minimal failure of the containment, then it becomes an unfeasible approach

diffeomorphism
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  • "Significant quantities" differs across applications. In my scenario for electric power generation aboard spaceships, a few milligrams...maybe 1 whole gram at the most, would be sufficient. I'm not sure how much you would need for spaceship propulsion, but if it's on the order of a few dozen tons, then yes I can see how it would be difficult to store. – DrZ214 Aug 10 '15 at 22:06
  • it still makes sense to store small quantities to catalyse nuclear fusion reactions – diffeomorphism Aug 10 '15 at 23:52
  • We still don't know what anti-matter in fact is and have only made enough to in theory bring a tea cup of water to a boil. – Doctor Zhivago Sep 02 '16 at 23:23