Time to build an electron injector by myself

Robthebob · Post by **Robthebob** » Tue Jun 29, 2010 12:19 am

As part of my quest to make a polywell fusor, first thing, I need to make an electron injector.

Currently the design would be something like this.
-Halogen headlight bulbs, cut off the envolope, on one end.
-Placed in glass container, not sure, in decent vac.
-positively charged mesh on the other end to accelerate the electrons.
-copper solenoid on the outside to create a b field inside that guides the electrons.

I hope the whole thing will be smaller than a regular flash light.

To increase the electron beam current, increase the power going through the bulb.

To increase the electron kinetic energy, increase the positiveness of the mesh.

Help please?

Solo · Post by **Solo** » Tue Jun 29, 2010 2:46 am

What are your goals for this? Just to test the injector, or to make one that you can attach to your eventual device? If you just want to make a test system, maybe a bell jar would be useful. Does your lab have one? Or perhaps you could fudge one by using a large test tube or round-bottom flask instead. Just watch out for stray electron beams - they can heat glass up till it shatters!

Also, what is your target for the injected current? How will you measure it? (Hint: Faraday cup?) Do you have a high voltage power supply? What's your budget, btw?

Robthebob · Post by **Robthebob** » Tue Jun 29, 2010 4:31 am

-inject into a polywell.

-I guess by using a rogowski coil.

-Yes, dont know if we can use it, but yes, but i doubt we will use that for the electron injector.

-shoestring.

ladajo · Post by **ladajo** » Tue Jun 29, 2010 3:49 pm

Check out the Australian setup. It is what Famulus is working on now (using his metal chamber).

D Tibbets · Post by **D Tibbets** » Tue Jun 29, 2010 5:27 pm

A car headlight filament with enough current to heat up and emit electrons near a cusp of the magrid.. That is all you need for an electron 'gun' like that used in WB6. The acceleration and focusing comes from the positively charged magrid. If you wish to have the magrid grounded, then you will need the high voltage electron gun. Bussard mentioned both approaches and settled on the positively charged magrid. It depends on issues like cusp plugging and other subtleties, but I presume the positive magrid is superior from electron recirculation perspectives.

[EDIT] And, of course, for a simple 'bastard' machine, you could use a central cathode much like a typical gridded fusor. This would invalidate the basic premise of the Polywell, but like in my permanent magnet setup (similar to WB1), it does show the magnetic cusps structures. The permanent magnets also modified the magnetic fields (the poles ran into the magnets- not good), but I wonder if this simple setup could test some of the confinement and transport issues, if you could setup the appropiate diagnostic equipment.

Dan Tibbets

GIThruster · Post by **GIThruster** » Tue Jun 29, 2010 5:53 pm

Can't just go to the junkyard and pull one off an abandoned CRT? Then you get a free focusing anode and one hopes, save a lot of time.

Robthebob · Post by **Robthebob** » Tue Jun 29, 2010 7:39 pm

good idea, i shall do that.

I'm a bit confused about one thing. (I have other confusions, but right now let's focus on this one)

From the aus set up (I read from the paper), it seems like there's no circulation, because the center electrostatic potential is directly related to the electron beam current. One would think that as you increase the electron beam current, there should be a point where the electrons will start to build up faster than the electrons getting lost. Unless there's no recirculation... or something...

also the injector should try to focus the beam current to a narrower cone, or does that matter? I've always been under the impression that the electrons should be injected into the system through the center of each of the faces of the cube, it would be easier for the electron to follow the field line to the center.

These things are all down the line, just trying to figure if the electron injector can just be a broken halogen bulb or if it has to be a little bit more fancy.

MSimon · Post by **MSimon** » Tue Jun 29, 2010 8:18 pm

GIThruster wrote:Can't just go to the junkyard and pull one off an abandoned CRT? Then you get a free focusing anode and one hopes, save a lot of time.

Depends on how much current you want. CRTs are in the 10 mA range.

GIThruster · Post by **GIThruster** » Wed Jun 30, 2010 12:05 am

Robthebob wrote:good idea, i shall do that.

Others here will know better, but I think you want to look for a CRT with the highest scan rate possible. The last series of Sony Wegas that used CRT's are about 8 or so years old? Might be a good place to start to look. Huge CRT's like ~35" lose vacuum over time and many will have been dumped by now.

Ideal seems would be an HD CRT with a big, bright, fast screen. Sounds like a Wega.

D Tibbets · Post by **D Tibbets** » Wed Jun 30, 2010 12:05 am

M. Simon beat me to the punch with CRT electron gun currents not being very much. Perhaps if you clustered a few dozen (or a few thousand)

.

Bussard gave some discription of how to establish a wiffleball, he either left out some details or I did not follow closely enough. Basically I believe you have to inject energetic charged particles at a rate faster than they leak out through the cusp confinement. As the excess builds up it starts pushing out the magnetic field until finally the wiffleball is formed. If you push too hard the cusps open up more- burps, prolapses, gives up and goes home?

Dan Tibbets

ladajo · Post by **ladajo** » Wed Jun 30, 2010 12:23 am

This is one of the key remaining issues not in the public venue.

Wiffleball effect is predicted, not confirmed.

It seems they are still not entirely clear what happens in the shell and cusps during fuel injection. WB8 is supposed to look at that as well.

They know something (<sic> positive) is happening.

The biggest two things we should see out of WB8 is a fully developed 3D model of the spikey ball, to include cusp interactions as well as plasma profiling. I think we will see that the well is not a well, but layered wells as others have discussed. I am thinking a certain amount of natural oscillation will result in these "standing waves" and maybe can even be enhanced by applying RF to the device ala something like POPs style. At a minimum it would appear to help with thermalisation...

thinking out loud...

Robthebob · Post by **Robthebob** » Wed Jun 30, 2010 1:37 am

MSimon wrote:CRTs are in the 10 mA range.

Apparently that's good enough. I may go smash up a CRT TV and get one sometime. since these are already focused, that's my job done for me.

MSimon · Post by **MSimon** » Wed Jun 30, 2010 3:40 am

Robthebob wrote:
MSimon wrote:CRTs are in the 10 mA range.
Apparently that's good enough. I may go smash up a CRT TV and get one sometime. since these are already focused, that's my job done for me.

Not so simple. You will get 3 electron guns. Color. And they are designed to be magnetically focused. And you have to cool the coils in a vacuum.

I'd go with the halogen lamps. They will scale better even if the initial work is harder.

GIThruster · Post by **GIThruster** » Wed Jun 30, 2010 4:50 am

Sounds like what Simon says. . .is right.

Just 35uA and 39.5 keV:

http://epsppd.epfl.ch/Hersonissos/pdf/P1_088.pdf

Still the idea of getting really fine focus in a free package is a good one if you can think of another application. . .

BenTC · Post by **BenTC** » Wed Jun 30, 2010 2:02 pm

MSimon wrote:Not so simple. You will get 3 electron guns. Color. And they are designed to be magnetically focused. And you have to cool the coils in a vacuum.

I expect the Red electrons will work better.