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

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Picture of 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:

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!

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Step 1: Design/Theory

Picture of 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.


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.
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Pyrophoric2 years ago
When one takes a doorknob to accelerate particles it's... glorious.
kelseymh2 years ago
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!
nak2 months ago

Very cool :)

I ran across this crowdfunding platform a while back:

It might be useful? I think I saw some other more science oriented crowd funding sites elsewhere too.

EmilyBug424 months ago

May I please have a list of materials? I am aspiring particle physicist and would like to do this.

Thank you!

chris0317967 months ago
I would just like to know how far you've gotten with your open-source accelerator.
egwillfriedel9 months ago
You should try to focus the beam with an electromagnet :)
jebersole10 months ago
Would it be possible to attach the anode to the bottom of the bottle?
egarcia151 year ago
Can I use copper for the anode?
That is intriguing - thanks, Xellers!
jcahill21 year ago
How could I do this project using different variables?
Could you use fluorescent highlighters for different color ray tubes instead of the phosphors from a fluorescent tube?
does this not produce large amounts of x-rays?
Xellers (author)  makincoolstuff2 years ago
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.
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 (author)  makincoolstuff2 years ago
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.
I wasn't able to detect any x-rays whatsoever coming off of my tube. I guess I was using a little lower voltage (a 6kv NST). Either way there is either no or negligible amounts of radiation coming off of this. I even tried reversing the polarity so the metal vacuum port was being bombarded with electrons (this is basically how ex-ray tubes work) and still no radiation was detected. For good measure I measured background for 5 min. and then turned the tube on and measured another 5 min. for each test. In no cases was the latter measurement higher than the former by a statistically significant amount (in fact a couple times it was lower).
ok, thanks for replying, so does that mean i wont be able to do this experiment with a fridge pump?
Xellers (author)  makincoolstuff2 years ago
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.
what pressure is the running at? because i have seen videos of people getting fridge pumps to works at 20millibar (10 torr)
Use an air compressor in reverse!? I know that works good.
a fridge pump is an air compressor!
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.
kleomenid1 year ago
Sorry to sound like a bit of an airhead, but what is the function of the diode?
The diode prevents half of the AC wave from going through it, effectively converting the AC from the NST to DC to power up the tube.
Are you still checking this thread? I would love to ask you a few questions about building a smaller version with my son for science fair.
ncortiz1 year ago
thank you ,
for the help,to make this very interesant project.
p1gnone1 year ago
Scientific American, Amateur Scientist [column] October 1967 had a sputtering project. As I am assembling needed components I was also learning of Crookes Dark Space. SO I happened on your very nice project. Hard to find in print, but this guy put all the archives on his webpage. If you remember this as fondly I do then this is an incredible resource. link:
scientist442 years ago
this was really cool to see and interesting to me i like it alot :D
AChillyDog2 years ago
You said you used a 15 micron pump, but what is the minimum for this project?
Ninjakaib2 years ago
You should have got your vacuum pump from here: It was only about 160 dollars. Also, how much did the neon sign transformer cost you. I got my wine bottle for free.
i got one of the same rating for $15 plus $18 shipping, the trick is to find a used non-GFI unit on ebay that is still guarunteed working,and buy from a top rated seller.
(referring to the Neon Sign Transformer)
longwinters2 years ago
It would be nice to get rid of the pump, if your seals are good you should be able to pump it down and disconnect it, (unless you like watching the process of pump down,it's quite interesting) You may get a little better vacuum if you warm the bottle to the highest temp. it can tollerate while under vac. then seal it off.

Very nice project being a person who enjoys High Voltage projects this looks like a fun one.
what isd its cost?
Higgs Boson2 years ago
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?
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.( 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.
Okay that answers the question. Thank you.
i also here that air conditioner's pressurizing pumps when used in reverse can create deep vacuum's
Xellers (author)  makincoolstuff2 years ago
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 =(
I have heard somewhere that a vaccum pump from an old fridge would do the trick.
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