VHS-Tape-Plasma Mirror Drives Tiny Particle Accelerator

When you think of a particle accelerator, you’re probably thinking of tens of kilometers of tube buried underground, at high vacuum, that uses precisely timed electromagnetic fields to push charged particles like electrons up to amazing speeds (and energies). However, it’s also possible to accelerate electrons in other ways, and lasers are a good bet. Although a laser-based particle accelerator can push electrons very effectively for a few centimeters, they top out at a relatively low maximum “speed” of a couple billion electron-volts, as opposed to the trillions of eV that you can get out of a really big traditional accelerator.

If only you could repeat the laser trick again, “hitting” the already-moving electrons from behind with another beam, you could boost them up to even higher energies. Doing so would take something like a one-way mirror that lets the electrons pass through, but that you could then bounce a laser beam off of. In a fantastic mixture of science and mother-of-invention-style hacking, these scientists from Lawrence Berkeley National Labs use plain-old VHS tape to make plasma mirrors to do just that. Why VHS tape? Because it’s cheap, flexible, and easy to move through the apparatus at high speeds.

The device works like this: a first laser beam passes through a jet of ionized gas and pulls some electrons with it. These electrons are then focused into a beam and pass through some (moving) VHS tape. The electrons punch a hole through the tape. In their wake they leave a hot plasma of mid-90s TV shows you never got around to watching. The second laser beam is then bounced off this plasma mirror and further accelerates the electron beam from behind. In principle, you could repeat this second stage enough times to build up the energy you needed, but for now the crew is working to characterize their single-stage beam. Getting the timing right on the second-stage beam is, naturally, non-trivial.

Anyone who has spent some time in a science lab knows that there are millions of these tiny get-it-done-quick hacks behind the scenes, but it’s nice to see one take center stage as well. If you’ve got stories of great lab hacks that you’d like to see us cover, post up in the comments!

Thanks [Bruce] for the tip, via Science Daily.

26 thoughts on “VHS-Tape-Plasma Mirror Drives Tiny Particle Accelerator

  1. Damn it! Those were the NASA moonlanding tape, 1st super bowl tape, 2 different J.F.K. tapes( one pointing at the grassy knoll and one at the library), and the area 51 security tapes! God damnit guys, be more careful next time!

  2. Don’t use billions and trillions, please. Use GeV and TeV. Billion can be 10e9 or 10e12 and sometimes it is hard to recognize the right number. You have many non-american readers…

    1. The world pretty much settled on 10^9 as a billion, the British one was too large for a lot of things. Plus it gives a nice series, billion, trillion, quadrillion, quintillion, etc. I think Dainbramage is the first person to say “milliard” in about 60 years.

      1. The world “settled” on ’10^9′ for 10^9, everything else is just windowdressing. Just for the record: In Germany, ‘Milliarde’ means 10^9. But why even use it like that? What ist the biilionth part of a trillion?Uh… What is 10^9 * 10^-14? 10^-5 ! Yay.

      2. And what world exactly would that be? All i know is americans use the short way, i don’t know anyone else using it. Maybe you just haven’t been in around the world as much as you think.

          1. This is a recent change (ok, maybe 20-30 years ago). The UK billion was a million million at one time (10^12). I remember the BBC world service using “thousand million” and “million million” to avoid confusion.

  3. Using a VHS tape and blowing holes down the center would create a lot of waste, as you end up with two strips of half as wide tape. What if instead they used a spinning (floppy?) disc? The electron beam would take nibbles out of the disc. if they move the disc closer to the center with each revolution the beam would be hitting a new patch of disc each time, with less wasted material.

    1. It’s easier to go reel to reel and have waste than it is to do the same speed with fine mechanical adjustment to avoid waste. Plus that’s a lot more effective area for the speed and simplicity. Tapes are readily available and to hand.

    1. Yes. You don’t even need to do it in vacuum. After the charged particles leave the evacuated drift tube through a low density “particle window” (beryllium foil is a common window material) they can strike a material of sufficient density to produce X-rays.
      The particle energy is so high in fact as to allow you to produce photo-neutrons, or spallation neutrons if accelerating protons or small nuclei.
      And all you need is a multi-million dollar tera-Watt ultra-fast laser and some old VHS tape.

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