Creating Antimatter On The Desktop — One Day

If you watch Star Trek, you will know one way to get rid of pesky aliens is to vent antimatter. The truth is, antimatter is a little less exotic than it appears on TV, but for a variety of reasons there hasn’t been nearly as much practical research done with it. There are well over 200 electron accelerators in labs around the world, but only a handful that work with positrons, the electron’s anti-counterpart. [Dr. Aakash Sahai] would like to change that. He’s got a new design that could bring antimatter beams out of the lab and onto the desktop. He hasn’t built a prototype, but he did publish some proof-of-concept simulation work in Physical Review Accelerators and Beams.

Today, generating high-energy positron beams requires an RF accelerator — miles of track with powerful electromagnets, klystrons, and microwave cavities. Not something you are going to build in your garage this year. [Sahai] is borrowing ideas from electron laser-plasma accelerators (ELPA) — a technology that has allowed electron accelerators to shrink to mere inches — and turned it around to create positrons instead.

There are two stages. One creates a high-energy electron flux using the conventional a conventional ELPA process. This stage creates a shower or flux of electrons. The second stage is where things get interesting. The electron flux bounces off a metal target which causes them to decelerate. However, that additional energy has to go somewhere, so it creates a gamma ray. The gamma ray however is unstable and converts into a low-energy positron/electron pair. Those low-energy positrons can be formed into a high-energy beam.

Unlike conventional methods, the only large part of this accelerator design is the laser system which currently takes about 25 square meters of space. However, as the laser designs get better, it should eventually be possible to build such a device on the desktop. If that seems crazy, look at what’s happened with electron beam generation. SLAC using conventional methods can produce a 1 GeV beam in a 64 meter-long track. The record for ELPA is 4.25 GeV over 9 centimeters and a 2 GeV beam has been produced in equipment measuring 2 centimeters!

Does this mean we are going to finally get our Space Ranger antimatter pistol we always wanted? Maybe. Meanwhile, you might have to settle for just the laser. It seems like most of the big lasers we see anymore are relegated to cutting.

28 thoughts on “Creating Antimatter On The Desktop — One Day

    1. Disclaimer: I’m a chemist, not a physicist, but I like physics. The annihilation of a single positron and electron, if I remember how to do this right, would result in the production of 1.64E-13 joules of energy via Einstein’s E=m*c^2 equation. In perspective, a firecracker releases approximately 30 J of energy (from what I can find online), so you’d need 1.83E14 events to equate to that energy, which 500x the number of stars in the Milky Way. Getting a single annihilation event would be little more than a fly fart in a hurricane.

      1. Tip: in particle physics nobody uses joules.

        The mass of an electron (and a positron) is 511 keV/c^2.
        (eV/c^2 is the best unit of mass for these things.)

        An e+/e- annihilation produces two photons (you have to get two, to balance their momentum) each with energy of 511 keV.

          1. Yeah, um, no. Outside of solid state physics and particle physics, maybe. What a shock: in fields where you’re concerned with individual electrons responding to volt-level potential differences, an electron-volt is useful. eV would also be useful for bond energies, but they typically use kJ/mol (or kcal/mol) because chemists measure bond breaking at macroscopic levels.

            “511 keV is totally abstract”

            So… why the heck is a joule not abstract? It’s *energy*. It’s all abstract. You know how much energy is in a joule because of reference points: it’s about the energy released by dropping a textbook about a foot. Same thing with kilocalorie: it’s the amount of energy needed to heat up a kilogram of water a degree. If the problem is that you’ve never been given a reference point for an electron-volt, here’s one: it’s around half the energy of a typical photon from the Sun. Or it’s about (1/6)th of the energy needed to split up a molecule of water.

    2. The lasers will take more energy that you’d get out of the electron/positron annihilation since they were essentially created from the laser beam. You don’t get anything for free….

  1. This will be absolutely fantastic if it pans out. The real hope is that we can store this and use it as a propellant for spacecraft. If we can then this is the first step toward interstellar spacecraft! :)

    1. Antimatter storage and production has been an active research field for years. You wouldn’t want to produce the antimatter at such high energies like this – you need them cool to store in a Penning trap.

  2. Remembering almost nothing of the actual estimated efficiencies from a writeup on antimatter production years ago, the lasers are going to have a much higher weapons potential. It’s also where I got a long running joke of mine, something along the lines of 100 square miles of solar cells is just the start.

  3. I currently create positrons in my garage. It is not as exciting as it first sounds.

    I have 100 kg (and exactly that: 4 of 25 kg bags) of potassium nitrate there. It constantly (well, at a slowly decreasing rate, after 1.25 billion years it will be only half of that – sad) outputs over 1 Megabecquerel of radiation. Mainly gamma and neutrinos, but also beta and ALSO positrons. The positron production rate is about 10 per second.

  4. “Jim ! Spock might be dying in there!”……. “if we let that thing into the ship, he’ll have a lot of company”…… “don’t misunderstand my next question – Mr Spock…. why aren’t you dead ?”……. “It’s that green blood of his”…… :) Obiligatory Trek nerd comment about episode referenced “Obsession”

  5. The authors say this method produces high-energy quasi-monochromatic positrons. Other than particle physics research, what is the practical use for such things?

    There is an antimatter factory a five minute walk from my house – a conventional medical cyclotron. They produce positrons on demand, all day long. And it’s the much more practically useful low-energy ones, mind you — for medical PET (positron emission tomography) imaging. (To the pedants, yes, I’m aware of the distinction that the cyclotron produces the isotope that then produces the positron.)

    Multi-GeV energies? Positrons via the pair production process from gammas? Yikes. Run that for a little while and it’s going to be hotter than Hades through neutron activation. Unapproachable and unserviceable. Maybe desktop size, but you’re going to need a few meters of concrete around it for shielding if you plan to generate any significant flux.

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