DIY Electron Gun
Background
I built this device for a competition called the Peterhouse Essay Competition. Its basically the exact same kind of thing William Crookes built when he was discovering electrons around 1869-1875. I figured that if he could do it 200 years ago, it couldnt be that difficult for me to do nowadays - which turned out to be pretty much true.
Design + Principles
(primitive GSCE-level physics knowledge required)
This is the exact same design as a Crookes Tube from the 19th century would use, with some modificiations to make it more DIY-friendly. The principles are the exact same though. There is a partial vacuum inside an airtight chamber. At one end of this chamber is a negatively-charged cathode, and at the other end is a positively-charged anode. Electrons fly from the cathode to the anode, and along the way some electrons will miss the anode, flying straight past and impacting on the glass. This causes a cool purple glow. This is a massively simplified explanation and isn't actually quite true, but its enough for you to be able to figure out your own design.
Wikipedia has a more accurate explanation:
Wikipedia
When high voltage is applied to the tube, the electric field accelerates the small number of electrically charged ions and free electrons always present in the gas. The electrons collide with other gas molecules, knocking electrons off them and creating more positive ions in a chain reaction called a Townsend discharge. All the positive ions are attracted to the cathode or negative electrode. Enough of the air has been removed from the tube that most of the electrons can travel the length of the tube without striking a gas molecule. The high voltage accelerates these low-mass particles to a high velocity. When they get to the anode end of the tube, they have so much momentum that, although they are attracted to the anode, many fly past it and strike the end wall of the tube. When they strike atoms in the glass, they knock their orbital electrons into a higher energy level. When the electrons fall back to their original energy level, they emit light.
How to Actually Make It
Estimated requirements: 2 days and ~£20
I wrote an indepth explanation of exactly how I made my tube for the Essay Competition I mentioned above.You can click the button below to see that in PDF form.
Eventually I might rewrite this in in a more condensed form and host it on this website properly, but don't hold your breath.
Contact
If you have found a mistake, have a complaint, or for any reason wish to get in touch with me, use the email below.