Can I make an electron gun at home?

genxium

I'm quite interested in home-made devices, last year I tried making a sinusoidal wave oscillator at home and succeeded. It feels good to DIY some coarse devices, and recently I'm learning to build a Cathode Ray Tube. However, it's not going successful with me; I would like to build an electron gun first, but the "emission mechanism" confuses me most.

From wikipedia, http://en.wikipedia.org/wiki/Electron_gun, it's said that there're 4 ways to emit electrons: thermionic, photocathode, cold emission, plasmas source. I want to avoid using high voltage source (not higher than 220V AC) at home, can anyone give me an advice ?

By the way, what I think of electron emission at the very beginning is a "metallic board" and an "electric field" that drives the electrons out of the board. If I want to do it in this way (maybe very unrealistic), how strong should the "electric field" shall I apply on the surface of the board to drive the electrons out of the metal (e.g. silver, copper, iron, cobalt, zinc)?

berkeman

I'm glad that you aren't wanting to try to work with several kV voltages while you are learning and in the DIY environment. Good decision.

I'd recommend that you do some reading about "vacuum tubes". They are relatively low voltage devices that use electron emission and modulation as part of their operation. For years before transistors were invented, vacuum tubes were the only way to implement diodes and amplifying stages. They are a lot smaller than CRTs too, which means that working with the vacuums involved is a lot safer. There are still safety considerations, but it is a lot less likely that you will hurt yourself working with a vacuum tube size volume versus a CRT.

What are you planning on using for your vacuum pump and glassblowing/sealing technique?

syhprum

When colour TV first started in the UK the available picture tubes had rather a poor life due to loss of emission from the cathodes.
As replacement tubes where expensive a cottage industry sprung up fitting new gun assemblies to the tubes and re pumping and re gettering them.
Eventually tubes improved and now they have been replaced by LCD panels but a few suppliers of gun assemblies might still exist in third world countries.

axemaster

If you are making an electron gun you should be aware that they can generate xray radiation. The xray energy should be proportional to the voltage difference the electrons are accelerated through. Additionally you should avoid terminating the beam in a heavy-atom material (like lead), since this will greatly enhance the xray energy due to bremsstrahlung.

It's much better to terminate the beam using plastic, since the atomic mass is very low (lots of hydrogen atoms). You can read up on this http://en.wikipedia.org/wiki/Radiation_protection. Read up on the parts about beta radiation, which is high energy electrons.

I do not recommend doing anything involving radiation unless you fully understand it. Most universities with physics departments or hospitals have a "radiation safety unit" that trains and certifies people to work with radioactive sources. While they probably won't certify you, you can at least get your hands on their training materials and study them thoroughly.



Final Note: Please be careful. The biggest danger of radiation is that you can't feel it. At all. You could be irradiated right now while you read this and you wouldn't know it. Also, typical TV tubes can and will emit xrays if you increase the accelerating voltage too much. If you don't know what you're doing, please don't just wing it. Ask a physics professor. Most of them really enjoy this kind of stuff anyway.

LuisVela

Hi
While working on a plasma device, we found the need to track the electrons downstream. We needed an emitting-electron probe (e-e probe) but we didn't want to buy anything expensive.

We found that a good way to construct one, was to use a lantern's light bulb (A good old Mag-Lite will do just fine, although be careful because the new ones use all LEDs. You want old Tungsten filament bulbs)

Once we got it, just get a glass cutter and cut off the glass around it. (we needed a small, localized source, so we looked for the smallest bulb.)

As you can imagine it is not a "gun" itself, since we used the magnetic fields of the device to guide and accelerate the electrons. This means that in order to make a gun out of it, you must have some magnetic lenses around or a voltage drop somewhere nearby. but that shouldn't be too difficult to construct either.
After some time we got fancier, but that was a funny and humble beginning =)
Best wishes.

genxium

Dear Berkeman: Sorry for replying so late (because I'm applying for graduate schools these days). I appreciate your advice and they seem really new for me (non-physics student)! I do want to try kv voltage and tried to produce it by voltage multiplier in our company's lab. However when things are to be carry out at home, I would like to compromise for my family :)

I have no idea about "vacuum tubes" except that they're "vacuum" and "ever used to make amplifiers". Can you provide some materials that're relevant to the DIY topic ? Links or name of books ?

genxium

Thanks so much axemaster. Actually my interest to DIY an electron gun (and maybe a CRT later) was partly from home TV set. However, I was not aware of the radiation problem. Here in China, home electricity supply voltage is at (220V, 50Hz) and it's now supporting billions of TV sets; Thus I wonder how such comparatively low voltage can work in electron emission since intuitively I thought e-emission should be done in a much higher voltage environment.

It's very nice of you. According to your advice I won't start making such device before I attend the graduate school and take safety courses, but I'm still interested in the principles (e.g. from what matters do I get 'electrons' and how to make a focus coil). They seem really interesting !

genxium

Sure LCD is much better in displaying ! I do esteem the tech evolution in display industry; however, I feel excited by electron guns because I'm curious about how people manipulate such tiny particles (though not exactly controlling a single one); thus I still wanna make one if possible :)

genxium

Dear LuisVela: That's a very nice idea :) I will try to get some magnetic lenses as long as they're not expensive for me. For this setting, I don't know how to get rid of the influence from environmental EM fields (which may influence the trajectory of electrons) so as to guide and terminate the electron beam. This should be a very traditional problem but I have no hands-on experience of it. May I get any suggestion from you?