Cold Plasma Torch Produces A Cleansing Flame That Never Consumes

It’s basically a lightsaber. Except smaller. And with an invisible blade. And cold to the touch. But other than that, this homebrew cold plasma torch (YouTube, embedded below) is just like the Jedi’s choice in elegant weaponry.

Perhaps we shouldn’t kid [Justin] given how hard he worked on this project – seventeen prototypes before hitting on the version seen in the video below – but he himself notes the underwhelming appearance of the torch without the benefit of long-exposure photography. That doesn’t detract from how cool this build is, pun intended. As [Justin] explains, cold plasma or non-equilibrium plasma is an ionized stream of gas where the electron temperature is much hotter than the temperature of the heavier, more thermally conductive species in the stream. It’s pretty common stuff, seen commercially in everything from mercury vapor lamps to microbial sterilization.

It’s the latter use that piqued [Justin]’s interest and resulted in a solid year of prototyping before dialing in a design using a flyback transformer to delivery the high voltage to a stream of argon flowing inside a capillary tube. The quartz tube acts as a dielectric that keeps electrons from escaping and allows argon to be ionized and wafted gently from the tube before it can reach thermal equilibrium. The result is a faint blue glowing flame that’s barely above room temperature but still has all the reactive properties of a plasma. The video shows all the details of construction and shows the torch in action.

Hats off to [Justin] for sticking with a difficult build and coming through it with an interesting and useful device. We’ve no doubt he’ll put it to good use in his DIY biohacking lab in the coming months.

19 thoughts on “Cold Plasma Torch Produces A Cleansing Flame That Never Consumes

  1. Please add UV reactive dye or film to the tip of the capillary tube as an indicator of successful ionization. Perhaps a tube of transparent UV reactive plastic a bit wider than the capillary tube that would be optically blocked from emissions deeper down the tube and only exposed to the tip.

  2. This is breathtaking! I don’t often watch the videos, but this one is so information-packed it’s well worth it, at least the first few minutes, for someone who’s sort of aware of plasmas but had no idea cold ones existed.

    I’ll be watching a bunch more of his videos when I get time!

        1. Pretty sure AKA and Martin didn’t actually read the piece or view the video. Or maybe they just have very poor comprehension of it. After all, it kind of looks like a TIG torch at first glance, so it must act like one too, right?

  3. Outstanding video and great work.
    I really do wonder about the efficacy of cold plasma though. Especially compared to easier-to-get alternatives.

    The “cold” plasma this produces is a mixture of energetic (hot) electrons and cold (room temperature) argon. The electrons very quickly thermalize. It even appears to happen within a a few millimeters of the tip: the thermalization process yields the energy that produces the glow, which stops just a few millimeters out. After the electrons lose their energy they aren’t going to be able to have any of the purported biological effect.

    Common practice for similar biosterilization applications is ozone (easy to make in situ) or, better; hydrogen peroxide vapor, which doesn’t have the nasty effect on plastics that ozone does. It’s already commonly used for whole-room sterilization.

    1. Cold plasma has different characteristics than any of the techniques you mention, and might be suitable for some cases. It should be tested, or at the very least be regarded as “something to try” for future applications.

      For example, a dentist mentioned to me the possibility of using this to kill cavity-causing bacteria after drilling and before the filling was applied. This might allow dentists to drill out less tooth than they normally would. He even suggested that this might be useful in killing all cavity-causing bacteria in a person’s mouth – apparently the bacteria live in tiny nooks and crannies within the tooth surface, which keeps them protected from normal treatments such as antibiotics. When the antibiotics are gone, the hidden bacteria cause cavities once more.

      1. I don’t think your dentist would think it a good idea to completely eradicate all bacteria from the mouth. There are a host of ‘good bacteria’ that are necessary for proper mouth hygiene.

    2. “After the electrons lose their energy they aren’t going to be able to have any of the purported biological effect.”

      I know someone who works with cold plasma and apparently the effects can be quite long lasting, something to do with the plasma generating oxidising species which can hang around in a sealed sample for much longer than I would have expected. They’ve been testing it with water which apparently retains bacteriocidal activity for at least a couple of days.

      It might not be a good one-to-one swap for other sterilisation techniques, but it could still have a lot of uses.

      1. Well, they’ve either made the water into a mild solution of hydrogen peroxide by shooting the plasma at it, or they’re selling another brand of homeopathy – any direct ionization effects should dissipate within minutes.

        1. “oxidizing species” could be just about anything, if there are other atoms around. Bromine, in particular, gets nasty when it gets oxidized into bromate, but even oxidized chlorine (from ordinary salt) could be relatively long-lived and potent.

  4. One place cold plasma really excels is in improving glue bonding, especially with difficult plastics. Surface treatment with the cold plasma will remove contaminants and increase the surface energy. I did some tests some years back and got a 5x improvement in bond strength between glass and LCP with a UV cured adhesive. The bond became so good it was the LCP breaking, rather than the glue bond. LCP is one of the ‘difficult’ plastics to glue to.
    The 5x improvement is not an estimate – we measured it with a pull tester.

  5. Have you tried this without a noble gas? Atmospheric pressure “air” cold plasma is being used extensively in medicine. The air contains oxygen, which when ionized become very reactive species.

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