I have repaired fusor III and it is up and running though I haven't completely chased all the water/virtual leaks out yet. Due to this, and limited time, I was only able to get about 62,000 n/sec out of the old veteran. But I will need another 5 hours or more of glow cleaning to move the bulk of the water out. (I am experienced with this routine)
The problem, as I mentioned on 14 Jan was the brand new spark plug replacement insulator broke down within its structure and gave a short above 1kv. I was so exasperated and busy trying to get the upstairs lab in order that fusor III was shoved off the the back burner.
I decided this would be a fusor III weekend and the spark plug is gone forever as they tend to reach a limit near 20-25KV. (they are still fine for demo fusors and low end fusion efforts.)
I secured one of the insulators designed for large capacitors which I found at a ham fest a year ago, machined its square silver plated base to a circular sheet metal section. I then took a rotatable conflat 2.75" fitting and bored out the center rotatable to accept the flange of the insulator and then silver soldered it in place. I next had to bore out the main flange to accept the isulator louvres in pass thru.
I machined a central copper post and added alumina sleeves for insulation and mounted the inner grid (1.5" diameter).
Done!
NO!
I now had to saw/grind/chisel off the old 1.5" oddball ASA type mini flange welded to the fusor half used for the spark plug. I next had to mount the half of the fusor designed to accept the new conflat to my milling machine and mill the opening out to 1.86"!
I, next, had to machine and rework a threaded 2.75 blank-off flange to weld to the fusor half. Boring a solid hunk of stainless out to 1.86" messed up two carbide bits.
Finally, all was in order and I tig welded the mating flange to the fusor half, reassembled the fusor and mounted the new grid mechanism which can now be completely changed out without disassembling the fusor body. (waste of indium wire each time I took it apart in the past.)
The assembly vacuumed down nicely to the single digit micron range in about 10 minutes. About 1 hour of glow cleaning and I could valve off the fusor and the pressure would hold with no active discharge in the <10 micron range for 15 minutes. (Adequate for fusion testing)
This is now a very tight fusor and after a few more glow sessions I should be able to get back to the old limit of 100,000 + n/sec.
WISH I HAD USED THE CONFLAT IN THE BEGINNING *&%$#@!*.....
The total time to effect this change was 17 man hours labor and effectively zero dollars out of pocket beyond the obvious tool wear and tear, weld gas and electric costs.
Richard Hull
Created on Monday, April 09, 2001 12:24 AM EDT by Richard Hull Last Modified on Wednesday, April 11, 2001 10:39 AM EDT by Richard Hull