DIY Electron Accelerator: A Cathode Ray Tube in a Wine Bottle

Learn how to build your own subatomic particle accelerator in a weekend! This simple project will allow you to investigate a variety of intriguing effects including magnetic deflection of an electron beam, Crookes dark space, plasma striations in a gas discharge tube, and many others. It can easily be used for a high school physics or science fair project and is compact enough to be demonstrated virtually anywhere.

You could be accelerating electrons to non-relativistic velocities after a trip to Home Depot and a visit to your local AC repair store and neon sign shop! Best of all, no advanced electrical or mechanical knowledge or tools are required.

Judges, see step 12 for contest entry details.

Here's some video evidence:

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Thanks for all the support, guys! This project was featured on Hackaday, Slashgear, Engadget, Gizmodo, Gadgetblog, Tecmundo, Matuk, Zedomax DIY, and Make, as well as in the weekly newsletter and multiple times on our own front page!

Please don't forget to rate/vote!

Xellers
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Step 1 Design/Theory

As complex as the idea of a particle accelerator might seem, it's actually strikingly simple to implement. The design we will be using was first created in the late 19th century by J.J. Thomson and subsequently used to make several important discoveries about the fundamental nature of the atom and the electron. Later, in the early 20th century, Cockroft and Walton (yup, the same hooligans responsible for the voltage multiplier) used a similar design to build the first true electrostatic linear accelerator, or "static linac" for short. Nowadays, advanced versions of this type of accelerator are commonly used for radiotherapy and ion implantation.

Essentially, our cathode ray tube is just two electrodes in a vacuum chamber with a high voltage applied between them. When enough of the air in the chamber has been removed, electrons will freely accelerate from the negative electrode (cathode) towards the positive electrode (anode). However, instead of impacting the anode and returning to the power supply, some electrons will fly right past it and keep going until they hit a glass wall.

Some interesting effects that can be observed at this stage are sputtering and magnetic deflection.

Sputtering:

If the acceleration potential is high enough, then some electrons striking the anode will have enough energy to knock metal ions right off the electrode. These ions will be deposited on the walls of the chamber near the anode and will create a silvery band somewhat reminiscent of the "getter" inside of an old vacuum tube.

Magnetic Deflection:

In physics, we all learned the Lorentz force law ( F = q[E + v x B] ), or the force on a point charge due to electromagnetic fields. In this context, it tells us that electrons will be accelerated from the cathode to the anode due E, the electrostatic field created by the high voltage power supply and that those electrons will also be accelerated by another field, B, in a manner that is dependent on the velocity, v, of those electrons. Since the velocity vectors of the electrons will be pointing roughly from the cathode to the the anode without an external magnetic field, we can use this to find out what effect a magnetic field will have if we introduce one.

Let's say we bring a magnet close to the tube while it's energized and we align it so that its field is roughly normal to the surface of the vacuum chamber. If we compute qv x B, we will find that the force due to the magnetic field is perpendicular to the paths of the electrons and to the magnetic field (by the definition of a cross product). In other words, the magnet curves the paths of the electrons and this effect is amplified by the duration that the electrons spend in the field. This effect can easily be observed inside of our cathode ray tube if a magnet is present nearby.

I've included a diagram of the mechanical construction of the accelerator to give a rough idea of how everything will work.

Comments

[kelseymh]

This is outstanding. One of the best at-home particle physics projects I've seen on I'bles (neither the cyclotron nor the fusion reactor have writeups :-).

Thanks especially for including the (non-relativistic) physics background!

[Pyrophoric]

When one takes a doorknob to accelerate particles it's... glorious.

[Ilija Miljkovac]

what isd its cost?

[Higgs Boson]

Your power supply had, as well as the voltage, a 30mA output. how much does current come into this. if you had a power supply that had a much higher voltage than the one used (say along the lines of 75kV) but a very low current of less than 1mA would the accelerator even still work, and if it did would X-ray production become a concern because of the high voltage? According to the safety step harmful radiation would be a problem, but would it still be a problem with the low current?

[oldschooltech]

I have read at one site that for most cases of cathode ray tubes, the x-ray radiation is not an issue of safety until one is run on voltages generally above 15kv of power.(http://www.sparkbangbuzz.com/crt/crt6.htm)although most cathode ray tube of the cold cathode type(same type as explained in the instructable above)are run at a MUCH lower voltage than 75,000volts. unless you are makind a screen 60 inces wide you probobly dont need such voltages.
hope my advice helps :D.

[Higgs Boson]

Okay that answers the question. Thank you.

[makincoolstuff]

i also here that air conditioner's pressurizing pumps when used in reverse can create deep vacuum's

[Xellers]

I tried building my own vacuum pump using an AC compressor, but it turns out that even a compressor from a pretty powerful air conditioning unit just isn't strong enough to pull the levels of vacuum required for a cathode ray tube. It was good for making mediocre gas discharge tubes, but not much else =(

[oldschooltech]

I have heard somewhere that a vaccum pump from an old fridge would do the trick.

[j.sadinsky]

Swell.

Quite posh indeed sir.

[moris_zen]

You really deserve the 5 stars kid - you have a great future ahead .
Well done and good luck .
Don't stop doing what you are doing - you will be the first I will follow on Inst'

[Xellers]

Thanks =)

[makincoolstuff]

does this not produce large amounts of x-rays?

[Xellers]

Nope - they don't have enough energy to penetrate the chamber with the acceleration voltage I'm using. Your concern is addressed in the safety step.

[makincoolstuff]

oh yeh, thats stupid of me. so is prolonged exposure to soft x-rays dangerous? and is using a fridge pump for vacuum and 30kv+ dangerous?

[Xellers]

Prolonged exposure to any type of x-ray radiation is dangerous, but this produces very little and should not be operated for long periods of time. You won't be able to get 30kV of acceleration potential with only a fridge pump.

[makincoolstuff]

ok, thanks for replying, so does that mean i wont be able to do this experiment with a fridge pump?

[Xellers]

You can certainly try, but I doubt it - you can definitely make a simple gas discharge tube, but I don't think it will full enough vacuum for good cathode rays.

[makincoolstuff]

what pressure is the running at? because i have seen videos of people getting fridge pumps to works at 20millibar (10 torr)

[brendonl]

Use an air compressor in reverse!? I know that works good.

[makincoolstuff]

a fridge pump is an air compressor!

[brendonl]

I mean one of those air compressors you use for air powered tools and all, there quite different in design. I am not sure which one works the best for drawing vacums.

[TheTower]

When exactly did you say you developed this design? I recall another video from about six months ago on Youtube instructing how to build the exact same thing. The design even appears to be the exact same thing. They even use an old wine bottle, just like you do. I was just curious because your video was dated
Aug 15, 2011, whereas this one is dated Apr 21, 2010. Here is the link to the "United Neko Technologies" Youtube video explaining in great detail.

[Xellers]

I never claimed to have developed this design, and my work is indeed partly based on that video (the wine bottle part). I'm going to mention that in my instructable.

Thanks for you comment!

[ohwason]

In my school (Thailand), all we have is a Philip Harris power supply which can generate up to 5kV, 2mA. Do you think this will be enough to make this amazing project? I really want to have a go at this! :(
this is the link to the power supply unit I am talking about ..

http://www.philipharris.co.uk/secondary/electronics-and-electrical-equipment/power-supplies/eht-psu-phe/?ev=search

[Xellers]

PM Sent.

[ohwason]

Sorry but Im new to instructables. Where can I find your pm message? It's not in my inbox...

[Xellers]

Click the top right "Inbox" button and then find and access the message you sent me - it should display both your message and my reply.

Hope that helps!

[ohwason]

There is nothing in there. Just my message to you under 'sent'. Would you mind sending it to me again please?

[Xellers]

That's odd, I see that I've replied to the message, but what I sent does not appear as part of the thread. Let me try again.

[ohwason]

Here is my email, you can send message to me directly :)
[e-mail]

cheers

[Xellers]

I just sent another PM, check your inbox in the next hour or so to see if it came (You should see "Inbox(1)" at the top right if this is so). If it doesn't come, I'll write an email.

[ohwason]

Still no luck on the PM... :(

[ohwason]

Still the same. 'You Inbox (0) Shortcuts Logout'

:(

[TheTower]

http://www.youtube.com/watch?v=813-2aAJ300
Sorry, this is the URL from the previous post

[paddys011]

does anyone know if a 25 micron pump would provide enough of a vacuum for CRT operation?

[Xellers]

Can you post a link? I'm absolutely sure it would, but it's always best to double check. You can always decrease your electrode spacing if the vacuum isn't strong enough. Sparkbangbuzz managed to make very good cathode ray tubes at hundreds of microns above what your pump can pull, but with electrode spacing of only a couple inches.

[mrworf]

brilliant!!! Good work man!

[Indegreen]

Hi Daniel-Good work, and very innovative with the wine bottle (be careful!). Where did the wine go? 2 things that may help. The tubing is outgassing while under vacuum and those gases are being ionized. After this, READ DANGER CAUTION: Unless you detach the center tapped ground on the NST internally, you are getting 1/2 the rated voltage from the NST. In your case-4.5kV. That ground is the true return path for current Floating the NST ground is not necessary, because what you have is enough to produce plasma. ***IF YOU detach that internal ground to get the rated voltage (don't do it!!!) , the case goes to full voltage potential and will/can kill you if you happen to touch the case. A floating ground NST should be enclosed in an insulated box (plastic tub can work). Please go to: http://www.fusor.net/board/view.php?bn=fusor_hvpower&key=1078245537&pattern=FAQ where you will find a much better description of what is going on than I can give. BE CAREFUL!!!

[Xellers]

Thanks for the comment!

I was considering removing the center tap on the NST, but I still need it to safely power my Tesla coil, and I don't want to lug it around in an insulated box. I used the NST/HV diode because that's what I had on hand. For my new cathode ray tube, I'm going to just build a super-simple flyback driver and get rid of the bulky, high current NST (30mA is way too much current for a cathode ray tube, so it needs lots of additional limiting, which is a pain).

As for the tube outgassing, do you have any advice on how to reduce that effect? From what I understand, cold cathode tubes actually need to operate in the region just before the plasma discharge extinguishes for electrons to be accelerated (sparkbuzzbang and my own experiments confirm this), but it would be nice to be able to get a lower vacuum for other experiments.