Jim Kovalchick -My attempt at smaller fusor

[Jim Kovalchick]

I have tried a magnet, but I will probably try some different configurations. I rushed my previous attempt for dose ALARA purposes because I don't like leaving my viewport shield off for very long.

[Maciek Szymanski]

I don’t think that a magnet can help. I suppose that the x-rays are produced not by the electrons impacting the glass but rather by the electrons impacting the metal shell on the opposite side. The viewport just passes them out as opposed to the metal chamber walls.

[Jim Kovalchick]

Maciek,
I absolutely agree that a magnet won't do anything for the xray problem through a viewport. Xrays are made copiously within my chamber, and they radiate everywhere. The glass provides very little attenuation.

The magnet discussion was more about trying to avoid the thermal damage the electron beam apparent by the dot fluorescence on the glass, may do to the glass. If the glass starts to crack, the port could fail catastrophically. The glass does get hot. I limit my run times both for glass heating and chamber heating.

Thanks,
Jim K

[Maciek Szymanski]

You can place a grounded metal mesh behind the viewport (vacuum side) to drain the eclectrons. It doesn’t have to be very dense, so it will not impair the camera image that much.

[Jim Kovalchick]

Yes. A mesh would work. I have also used a sacrificial piece of glass in a past fusor.

[Frank Sanns]

I have a round piece of leaded glass that is barely yellow and does the job of shielding from electron beams and x-rays. It is good up to around 40kv then x rays start leaking from feed throughs and the shell but it is nice to have in place when you need to see into the dragon's lair.

[Jim Kovalchick]

I studied an image taken last night during a run at 37 kV and 7.5 mA. I thought I saw a well defined ring of color in the middle of my grid. I cut the image to just the grid, removed the color and enhanced the contrast. Now the ring is very visible. In the black and white photo I am referring to the wide, dark band. I looked the port this morning and I can see that the grid has a faint band in the middle. The grid does have thinner edges but it is gradual, not a step change.

I looked back at images of Jon Rosenstiel's grid after he removed it, and there are blue rings of color on the edges. Maybe this is the start of the same thing.

I wonder what phenomenon is causing this.

[Jim Kovalchick]

Yesterday, I pulled the outer layer of lead off my fusor while I looked for a vacuum leak. Here is a photo of my cross with painted white lead strips on the cross's legs. The discolored paint leaves no doubt where the heat is found in a single axis fusor.

[Dennis P Brown]

Good pratice to paint over lead sheet.

My high voltage feed thru required a fan to keep it from over heating and I ended up needing water cooling of my chamber since after thirty minutes it was far too hot. My system was pushing 1200 watts thru it.

[Jim Kovalchick]

Dennis,
If I pushed 1200 W into my fusor for very long, something would fail. I usually run around 400 W.

Jim K