DIY: Baby Plasma Cutter [W/Video]

DIY: Baby Plasma Cutter [W/Video]

Pencil lead and some batteries make a small plasma cutter that is used to etch a pattern in aluminum foil.
In this simple but cool demo, you are able to observe how a high velocity ionized gas (plasma) conducts electricity across a small gap between the tip of the pencil lead (graphite) and a conductive solid (aluminum foil). When electric current is applied, the carbon atoms in the graphite vaporize and ionize creating a small ball of plasma that heats and melts the aluminum foil.

Let us know if you think this demo is something you would use in your classroom. See comments below!!!

This video was produced by The Little Shop of Physics at Colorado State University in partnership with GE.

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Comments (22)

  • Bradley Rausch Reply

    I will try the demo, but I will not use the video. The guy says “tin” foil and “lead” a bunch of times instead of saying “aluminum” foil and “graphite” respectively.

    February 5, 2016 at 7:19 pm
  • James Dean Reply

    How did his use of “tin” foil when referring to aluminum foil get by the reviewers?

    February 5, 2016 at 7:20 pm
  • NAult Reply

    Excellent idea! A great way to explain plasma and be able to show a practical use for it all in one quick and interesting demo!

    (Suggestions: refer to components as aluminium foil and graphite instead of tin foil and lead.. even if it is a pencil lead. This will be easier for students to follow and correct terminology for a science class)

    February 5, 2016 at 7:24 pm
  • James McIntyre Reply

    Cool idea. Great demo.

    February 5, 2016 at 7:31 pm
  • Todd Pedlar Reply

    Yeah, the whole “tin foil” and “lead” thing grated on me pretty bad. Definitely will do the demo next week in class 🙂

    February 5, 2016 at 7:34 pm
  • Farrell ROgers Reply

    I agree about the terminology. Could be used as an op to talk about common terms used to describe things that are obsolete. The apparatus is awesome and other than that, he does a fine job of describing the process. Not sure about the word consumed either, but I can ask kids “what does he really mean?” and apply the LoCoM&E.

    February 5, 2016 at 8:24 pm
  • Phil Arnold Reply

    With a carbon arc, as little as this may be, care should be taken to prevent burning the eyes of the participants. That just like looking at the sun.

    February 5, 2016 at 8:29 pm
  • Paul Jebb Reply

    Excellent demo! This integrates beautifully with a current event that happened this week. Angela Merkel, the Chancellor of Germany threw a switch to inaugurate Wendelstein 7-X, a fusion reactor that corrals a plasma stream in order to do experiments that will crack the fusion energy question.
    A lot of students don’t really know what plasma is. So this demo helps to make plasma less of an abstraction. As a segue to this, most students don’t know that a candle flame is also a plasma stream rich in ions. Many physics teachers have a tesla coil in the back room. When discharged to a lab faucet, we can see the plasma stream. The plasma stream can be widened if a candle flame is inserted in between the tip of the tesla and the faucet.

    February 5, 2016 at 8:40 pm
  • Jay Shelton Reply

    I like it. I’ll do it.

    February 5, 2016 at 8:44 pm
  • Mark Godwin Reply

    Yes I’ve done this. Works well especially if you crinkle the foil and have sharp edges, then simply hold a pencil to it.

    February 5, 2016 at 9:22 pm
  • Mary Reply

    Besides the smoke that is given off by this cutter, are there any other possible safety concerns one should be aware of?

    February 5, 2016 at 9:59 pm
    • Arbor Scientific Reply

      We have reached out to Little Shop of Physics and will post their response ASAP!

      February 8, 2016 at 9:09 am
  • Ryan Reply

    Fabulous idea. Thanks!

    February 8, 2016 at 12:20 pm
  • Kim JOnes Reply

    This looks like something I would try in my science classes. Thanks.

    February 8, 2016 at 6:46 pm
  • Tim Reply

    I was reading that this is really electrical discharge machining (EDM). The light is so bright wouldn’t welders goggles be advised?

    February 13, 2016 at 2:47 am
  • John Reply

    A very nice & inexpensive demo, with a lot of science to consider: cells in series, anode, cathode, open/closed circuit, C, Al, ionization, etc. I agree with the other folks who commented about the correct terminology. This is the chance to do it, with the attention that this will draw. Also, I’d question the eye safety aspect, too. There’s probably a lot of UV there – it is not good to look at such a bright arc without protection. As someone who was legally blind due to cataracts (and who can now see very well due to lens implants), a thing like this becomes very meaningful. Thanks for the video but let’s find out about the effects of the demo on young (and old) eyes.

    February 17, 2016 at 6:31 pm
  • David Reply

    I love the demo, I think students would find it very engaging. I’m not troubled by the casual use of language in the video.


    (1) how could the demo be augmented to convince students that what we’re seeing at the tip is plasma? I would hope that some of my kids would push back along the following lines: the point of contact is small, I don’t know much about graphite but I bet it doesn’t conduct well, so if we push a lot of current through there it will heat up and the heat is just melting the foil.

    (2) how can we get a read on the amount UV being given off? Many years ago as an undergrad I got serious welder’s flash when the lab tech set out the wrong power supply for gas discharge tubes. My partner and I both ended up in the ER that night. My department head’s hair would stand on end if she saw me do this demo now without proper safety precautions or testing. “It looked safe to me” is not what you want to say to a judge after a kid gets hurt.

    February 17, 2016 at 6:50 pm
  • Victoria Reply

    This is a great demo except the reactant used are not as stated. The carbon that vaporizes to plasma is from graphite not lead, and the foil placed over the basket is not “tin” foil but aluminum foil. These errors are made continuously throughout the video presentation.

    February 17, 2016 at 7:38 pm
  • April Reply

    They did a great job saying “tin” foil is a common mistake. It’s mostly the term used at home. No worries really!

    February 17, 2016 at 11:55 pm
  • Twyala Reply

    Mine will not work. I get a couple of sparks, but nothing else. I checked the voltage on the batteries and I am good there. Any suggestions?

    February 22, 2016 at 4:32 pm
  • David Headly Reply

    I was able to recreate the burn. I do not believe however that this is a plasma cutter – did the company get this description from someone in that field? I took some measurements and did a calculation for anyone interested – here are my results:

    The latent heat of melting of Aluminum is 321 joules/ gram
    using the density of Al = 2.7g/cm^3, and the radius of the graphite stick of 2.5E-4 meters (.5 mm thickness as in video) and thickness of the foil at 2.45E-6 m, I get the MASS of the piece of Al directly below the graphite at any moment as only 13 picograms ! That means the energy needed to melt that small area is only 4 nano joules.

    The current I measured in this process was about0.7 Amperes, and therefore the power delivered is

    V I = 36 V x 0.7 amp = 25 joules per second – WAY more than is needed to melt the Al, due to the high energy density. To create a plasma from only 36 volts, you need a gap of about

    36V/3E6 V/m = 12 micrometers – it MAY be happening that just as the tip gets a millionth of a meter away from the foil, plasma is created, but there is no way to see that level of detail. I also don’t know why aluminum carbide is not formed from the heat – graphite + Al plus energy gives

    Al4C3 but I saw no such deposit on the foil or accumulating underneath – perhaps the amount of Al reacting is way too small for detection visually.

    To sum up I think the only thing that is happening is that you are melting the Al foil under the electric power supplied, not by creating a plasma cutter. If there is a way that Arbor has tested this and found I am wrong, please let me know – very interested !

    April 11, 2016 at 2:05 pm
    • Bruce Rea Reply

      This video was made by The Little Shop of Physics at Colorado State University in partnership with GE. We have not tested ourselves, nor do we have the background in-house. Thanks for your comments David.

      June 7, 2016 at 2:11 pm

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