Introduction: Plasma in a Test Tube
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
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:
- https://www.instructables.com/id/ZVS-Driver/ thank you so much Plasmana
- https://www.instructables.com/id/2n3055-flyback-tr... 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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Please be positive and constructive.