Plasma in a Test Tube




Hi everyone!

This is my second Instructable and english is not my mother tongue, so I ask you guys some patience for the possible formal inaccuracies.

I decided to enter this Instructable in the Teach It! contest, so I ask you to vote it, if you feel it deserves it! I belive that it fits that contest because by this Instructable you are going to learn how to deal with the fourth state of matter: PLASMA, that i think is not just trivial stuff. Indirectly, you will also learn a bit of glass working.

Disclaimer: if you are going to reproduce this Instructable, be aware of the risks it concerns: deadly high voltage current will be used and the final product may be able to produce a little amount of x-rays. I'm not responsable for any damage to property or persons, due to the imitation of this tutorial.

Step 1: What Is PLASMA?

Even If the aim of this Instructables is not to make an advanced lesson about the plasma phisics (I'm not able to do it), but only to teach you how to produce it, it may be a good thing to have a vague idea of what it is.

You may be accustomed to the first three states of matter: solid, liquid and gas. But there is a less known state called plasma, that ironically, is the most abundant form of matter in the Universe. Thats because most stars are in a plasma state.

Technically, plasma is a ionized gas that consists of a set of electrons and ions but globally neutral.

A neutral gas is dielectric (this means it can't conduct electricity) but if it is subjected to an sufficiently strong electric field, at a sufficiently low pressure, it ionizes. It means that its particles lose their natural electronic balance, and starts to conduct electricity.

Lightning is an example of plasma visible on earth. And since plasma is extremely hot (in a lightning it can reach temperatures of 28,000 kelvins) is often used in industrial cutting.

In practice, all this results into a charming glow of light with a color ranging from purple to blue.

Step 2: Materials

For this Instructables you will need the following items:

1) Some thick and big test tubes, mine was 20cm long and 2cm Ø

2) A cork cap that closes hermetically the test tube

3) A 7cm long 0.5cm Ø metal pipe. Mine is brass made, but it doesn't really matters.

4) A 10cm long 0.5cm Ø flat head steel bolt. The head is 1,8cm Ø so it fits the test tube.

5) Some insulation tape

6) Some epoxy

7) A short piece of iron wire

Step 3: Tools

For this instructables you will also need the following tools:

1) Butane torch.

2) Heat resistant gloves (these are fundamental!)

3) Grinding wheel

4) Drill

5) Pliers

Step 4: Special Equipment

The title of this step may have crushed your expectations: "Will I need some special equipment? You said it would be easy!" Yeah and it will be! To run the device you will also need:

1) A high voltage generator that can push out at least 15-25 Kv at 50-200 mA.

Mine is just a simple ZVS circuit, driving a flyback transformer. If you don't know what I'm talking about, you should check this great Instructables that I followed to build my generator:

- thank you so much Plasmana

- and thank you too Alex1M6

It's really easy to do, you can even buy a ready-to-use circuit on ebay for 25$ if you are not good at soldering. If you have it, you can even use a neon sign transformer.

2) A vacuum pump.

Vacuum pumps are expensive, thats why I'm using an old compressor form a refrigerator. I just attached a thick pvc tubing to the suction end. It works really well.

Step 5: What Are We Going to Build?

We are going to build a cilindric vacuum chamber with two electrodes. After the vacuum making, rarefied air will remain in the chamber. By creating a strong electric potential difference between the two electrodes, the gases inside will pass at the sate of plasma.

You can look at the picture for more details.

Watch the video in the last step to see it working!

Step 6: Preparing the Cathode

The bolt will be our cathode, but first you have to do a few modifications:

- Sharpen the end of the bolt using the grinding wheel. This will make the glass piercing passage more easy.

- If the bolt is galvanized, remove the zinc coat from the head. Due to the high temperature it will reach, it may be flaking and smudge the vacuum chamber.

Step 7: Preparing the Anode

The anode block will also be our attachment for the vacuum pump. You will have to:

- Drill a hole in the cork cap, just a little tighter than brass pipe.

- Push the brass pipe all through the cap, leaving at least 5cm of pipe in the inner end.

- Wrap the wire around the outer end of the pipe, leaving a couple of cms straight.

Step 8: Mounting the Cathode

Now there is the fun part: you have to inglobate the anode in the back of the test tube, leaving an uncovered part of the bolt to attach the generator. It may sound difficult, but I found out that glass-working isn't that bad. You will have to:

1) Wear safety gloves

2) Heat up with the torch the back of the test tube to soften the glass. The best way is turning it constantly on the flame, making a 30° angle as shown in the picture. It will be ready when the flame will turn orange from blue, ad the glass will glow orange as well. Using multiple torches will make everything more easy.

3) Push the bolt through the soft glass FROM THE INSIDE. This will shape a glass protuberance.

4) Break the end of the protuberance, as the bolt can pass through.

5) Heat up the glass protuberance and making it slowly collapse on the bolt.

6) Seal the glass protuberance against the bolt, clamping the soft glass with the pliers.

Read the tags on the pictures for more details.

Step 9: Sealing the Cathode

The result of the previous step may be imperfect. To check this it will be sufficient to blow through the test tube.

If you feel any air leak from the bolt area, you will have to seal it with some epoxy, or wrap it with some insulation tape. Tape works better because by pumping vacuum, it will bend, filling the leaks itself. It is also easy to change if you need to.

Step 10: Set Up Everything

Now it's time to set up the device:

1) Assemble the chamber. If you did everything right there should be 12cm of distance between the two electrodes.

2)Put the chamber in a secure orizontal position. To achieve this, i made a simple plywood stand. Cardboard will do fine as well. (I flew over the base making steps, but you can see anyway some pictures of it).

3) Attach the vacuum pump to the anode.

4) Connect the HV generator to the electrodes.

5) Run the vacuum pump.

Now everything is ready for the show!

Step 11: Watch It Glow

After reaching a good vacuum just start the generator. A clear stream of plasma appears to your eyes.

Stream deflection: since plasma is sensitive to magnetic fields, is possible to deflect the stream with a strong enough magnet (as shown).

Since plasma is etremely hot, is not advisable to keep the device turned on for more than 30-40 seconds.

I hope you guys enjoyed my instructable and I hope you've learned something new, let me know!

And again, vote it at the Teach It! contest if you feel it deserves it!



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    44 Discussions


    Question 4 months ago

    I have a Solid state transformer 12 kV, 35 ma I assume that way too low to generate Plasma this way. It also cannot handle a load so would a vacuum like that produce a load quickly burning out the transformer? Please, when you have the time could you answer quickly.

    Would rectify it with DC work any better? I am wondering rectifying it to 25 kV to 36 kV work?

    Actually I'm working on a co2 laser, but there is a big obstacle: i need a NaCl lens and i have no idea where to find it for cheap. Im thinking about to build one by myself but i know its a desperate attempt..

    SHOE0007Peris The Majestic

    Reply 4 months ago

    Yeah, you need O rings to create a high-pressure vacuum at high atm and pump CO2 with nitrogen and other gases. I studied in Photonics and did a thesis on building a Nitrogen laser.

    You need rectifiers usually to get to 40,000 volts and cooling. The hardest part would be the NaCl lens for a CO2 laser. You can get tubes of CO2 but they are 8-10 grand.

    It really hard for anyone to find unless your super rich to build a CO2 laser. However, it can be done. And no moisture present or the NaCl lens would be destroyed.


    5 months ago

    better video take off!


    2 years ago

    Awesome project!


    2 years ago

    Once you have the finished product is there a way to transfer the plasma into a magnetic field for a sustained amount of time, or would the plasma simply revert back into gas once it was outside of the test tube?


    3 years ago

    Can you put a tuned transformer over the tube to set up a ion inuction and electromagnetic induction ionization loop with power removed for a power source?


    4 years ago on Introduction

    I'm only in high school and I know nothing about electronics, I need easier to follow plans for the ZVS Flyback. Can anyone help?


    4 years ago on Step 11

    disregarding the exposed electrical part, there are risks in using?


    um, not to be a downer, but no. it isn't.

    a confined plasma inside an evacuated chamber is one thing, and relatively easy to accomplish (hell, an incandescent lightbulb and a suitable HV supply will make a cheap and dirty plasma ball), a confined plasma channel in free air that self terminates and carries enough current to cut through things (as lightsabers are depicted) is... let's just say that it is not feasible given the state of the art in plasma physics. the energy requirements alone would be nearly impossible to reach in any sort of a portable form, let alone something the size of a sword hilt; to say nothing of the small problem of generating a self collimating and terminating plasma channel.

    it may be possible, eventually, but as it is right now, lightsabers are still firmly in the realm of science fiction, despite what various popular science type shows might tell you.

    if you're interested in plasmas and the interesting things that they can do, I highly suggest starting with the wikipedia page about plasma; if you want something of a more exotic idea to spark your imagination, try searching google or wikipedia for "electrolaser".


    Reply 4 years ago

    you forgot something also the force and pressure of the plasma would be to immense to properly stay in one place without being contained


    4 years ago on Introduction

    Your way ahead of where I was in 8th grade. =), Just need to brush up on some of the underlying laws that govern electricity. try's_law and's_circuit_l...

    Just remember to have fun ;)


    4 years ago on Introduction

    "electricity always flows on the path of least resistance" or more commonly "Electricity always takes the path of least resistance". This is something I hear a lot and isn't really correct. Electricity (the flow of electrons through a conductor) will take every path that leads to a ground (makes a circuit). Only the amount of current (amps) will be determined by the resistance.

    Take the simple parallel circuit diagram I uploaded. If R1 =1ohm and R2 = 1000 ohms. Then people are saying that current will only be measured on the branch that R1 resides on. This isnt true. While most of the amps will be measured through R1. The second branch will have the same amount of Volts and some Amps. Yes the Amps are much less because of the higher resistance, but their is still current flow.

    1 reply

    Thank you for your accurate answer! I read somewere that there is an equation that bonds the values of: the distance of electrodes, resistance of gas, moles of gas, and difference of potential between the electrodes but i can't find it anymore. Do you remember it?

    1 reply