Electron Gun Tweaks

20 10 2011

All photos.

Today I tweaked the electron gun.

My goal is to bring the electron gun closer to ground. This should reduce the pressure needed to strike a plasma.

I used Stuart’s DIY spot welder to make a hoop from welding wire:

I installed this hoop on the electron gun:

This arrangement brings ground potential closer to the electron gun.

And it worked somewhat.

With this hoop, I can strike a stable plasma at 18 millatorr. Better than yesterday’s 25 millatorr. Still needs work to get back to 8.5 millatorr.

When I went to fire the coils I discovered my SCR is shot:

Turns out the SCR’s peak current is 2,000 amps. At 2,300 amps we are well beyond that!

I have to order a new SCR tonight. Suggestions welcome.

Elsewhere… I drilled a hole in the langmuir probe holder to allow trapped gas to escape:

Also tested out the supercapacitors in my friend Arnie’s forklift:

They were able to lift Arnie twice!

Video of operation:

From CRT to Electron Gun

6 10 2011

This post is dedicated to Steve Jobs. Hero, and inspiration to all.

All photos.

I bought a second CRT; broke the vacuum by drilling an unused pin; scored it and smashed it!

Now we have an electron gun:

I installed it in the chamber and wired it up:

Here you can see down the beam line to the hot cathode.

I taped a piece of broken phosphor screen on the viewport so I can see the electron beam:

But something is not working, no beam.

Time to troubleshoot.

CRT in Focus

19 09 2011

All photos.

I finished the CRT power supply and got the CRT running with focus and grid:

As you can see we have an interference pattern. To the eye the beam looks much brighter in the center:

With the focus adjustment I can broaden the beam:

The CRT power supply:


Electron Gun Operational!

29 08 2011

All photos.

Electron gun operational:

I got these high voltage supplies made for CRTs:

I still need to play around to get it focused, but a great start!

New Parts: Cathode Ray Tube, 3D Ceramic Test

18 08 2011

I bought an old oscilloscope CRT at Leeds Radio. RCA-3BP1

I will eventually break this tube (implosions! I know!) and use the electron gun and phosphor inside the vacuum chamber.

The idea is to run the sydney experiment with a pure electron beam. We are currently using an air or deuterium plasma.

Before I break the CRT I will operate it in tact. Here is the pinout for 3BP1.

This sweet CRT hack is a good start for the power supply needs.

Already got the hot cathode running:


On the 3D printing front I received the 3D printed ceramic coffee cup I ordered last month:

It looks really promising. Soon we’ll have a 3D printed ceramic magrid.

Sydney Experiment: We Have Electron Confinement!!!

2 08 2011

All photos.

1 year,  7 months  and 8 days ago I learned of the copper coil Polywell that Joe Khachan and his team built.

I decided to repeat Joe’s experiment. Although challenging it seemed possible to achieve. I dubbed this endeavor the Sydney Experiment.

It took far longer than I expected to fabricate all the necessary parts for the experiment.

Today with great pleasure I ran the Sydney Experiment. Here we see what appears to be electron confinement:

This acquisition shows the floating potential of the langmuir probe.

This run was done with air plasma at 10 millitorr :

The electron gun was running  10KvDC @ 6.5mA:

The coil power supply was charged to ~ 400VDC:

This is just a first run. Now begins the actual experimentation and data gathering.

I do believe this is the WORLD’S FIRST AMATEUR POLYWELL!!!


The plasma during the run:

Electron Gun: Spark the Plasma

19 07 2011

All Photos.

Just completed a test of the new electron gun with air plasma. Looks good:


To get here I had to reconnect all the ground leads:

And wire up the high voltage:

Electron Gun

27 03 2010

Now thats it’s so much easier to open and close the conflat, I decided to take another shot at the electron gun. This time I got it. These are air plasmas.

You can see an electron beam evident in this photo:

Electron Gun

12 01 2010

Yesterday I was at the lab (which is absolutely freezing, the boiler is broken). I installed the electron gun:

I fumbled the flange when I was removing it, and broke the ceramic tube. Ugg. I’ll have to make another one.

Notice the ceramic’s discoloration from the plasma of the Fusor. Why? Plasma is corrosive, but still rather surprising to see such a dramatic change.

Unfortunately, I installed this incorrectly: a centimeter of the lead wire is unprotected by ceramic. The plasma was forming around this lead.

So I’ll have to open the chamber back up and try again. I think it’s time to invest in a powered torque wrench. Doing the large conflats by hand is a real time consuming pain in the ass (and knuckles when the wrench slips).

Another useful upgrade are these plate nuts:

These are metal plates with two threaded holes, shaped to match the corresponding CF flange’s bolt hole patterns and replace the individual nuts. The plate nut’s major advantage is, once two bolts are manually started, the plate nut acts as its own backing wrench and washer—the bolts are tightened using one wrench.

Coil Former and Electron Gun

6 01 2010

It’s looking feasible to run the Sydney experiment. The pieces I need beyond my current setup include:

  1. teflon coil formers
  2. electron gun
  3. coil drive electronics
  4. Langmuir probe

The coil formers will be turned on a lathe. I’m going to refer to these as coil formers, because unlike a magrid they do not carry a positive high voltage potential. The 2.5″ teflon rod arrived yesterday:

The electron gun is pretty straightforward. A metal cylinder placed at -10 kV in a few millitorr of hydrogen gas will produce the beam that you see in the Sydney experiment. I’m about to braise this copper tube to a lead to make the electron gun:

The coil drive electronics: Provided I can get the schematic, assembling the coil drive electrons should be straightforward.

The Langmuir probe: Still waiting to get quotes. Although the Langmuir probe looks pretty complicated, hopefully a commercial product will allow me to approach it as a black box… just a tool for taking plasma measurements. This exploration will force me to delve deeper in to plasma physics.


Joe Khachan has the following to add:

You are probably better off tapping a hole in the cylinder for the electron gun and screwing the stalk into it. This will get hot and brazing might melt. Another note, commercial langmuir probes might be a little limiting since they are made for the plasma processing market and will scan between -100 and 100 V. The polywell will be dealing with greater voltages than that. We make ours, which is a simple construction. Just a very thin wire (the width of a human hair) inside a ceramic sleeve, about 10 mm of the wire is outside that sleeve at the center of the polywell. You can find details on the web since many people make their own. For floating potential you can use a high voltage probe connected to the langmuir probe wire and the output of the high voltage probe goes to the oscilliscope, which is what we were using. These are the time varying potential that you see in our powerpoint presentation. After you’ve finished, you will find interesting behaviour in the well depth as you change the current in your coils.

Another note. The electron gun relies on the natural break-down of the gas in your chamber like gridded IEC. The breakdown voltage and/or pressure will depend on the size of your chamber (if you don’t have another ionizing source). You may have to increase the pressure until you get breakdown – then you can reduce it after that. You want as low a pressure as possible since the electrons are trapped for a long enough time to collide significantly with the background gas and therefore lose energy and therefore potential. If you have to go above 10 mTorr then so be it. You should still see interesting behaviour.

The langmuir probe should be the simplest of all that has to be done. Just ignore the wikipedia page. The maths makes it look bad. It is just a wire connected to a voltmeter (for the floating potential). You just need to shield most of the wire with a ceramic sleeve and only have 5mm to 10mm exposed in the plasma – that’s it. You will need electrical feedthroughs on your vacuum chamber so that you can connect the langmuir probe wire to the outside world.

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