Test run with new oven and some more shielding

Data from actual runs of fusors goes here, we can discuss it elesewhere in other sub forums I will create as needed -- let me know.
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Put data and fusor information from actual runs here. We'd like to know how well you are doing, and how you did it in some detail here. We can discuss elsewhere, this is for real reports from actual experiments only, or at least, mainly.

Test run with new oven and some more shielding

Postby Doug Coulter » Sat Jul 26, 2014 3:14 pm

While the fusor worked great - this is getting good - it now idles at around 2-3 million neuts/second - the leak prevention efforts seem to be an all or nothing thing - just one tiny hot leak is enough to make things lots worse. X rays seem to scatter like a flashlight in fog, and if there's one nasty leak, it make the op position hot. We've improved over what we had by a fairly big single integer factor, but we want more like 10-100 times better to make it safe to take this thing above idle (where we've seen 30 million neuts/second, or 10x idle, almost without trying and definitely without tuning).

But since I did run for a bit...here's what that run looked like to my data aq (using a new intel NUC, but that doesn't change anything but saving power and noise - and space).
NewOvenTest.png
Plots of this run.



FWIW, before this run, I tried totally encasing the standard geiger plotted here in lead bricks, 2" thick. No change in the background whatsoever, whatever that means. Either cosmic rays ignore 2" lead (we know that some do, but maybe not secondary shower stuff) or there's some contamination in the counter itself (common if I read the books right) and that's our background. You can see where at around 230 seconds I just put a lead brick on top of the counter and it goes back to background, so this is all fusor stuff and 2" stops it all. I should have (and will later) a 1/8" piece to get a poor man's spectrum of what is getting to me here. A few thicknesses should separate the big capture gammas from the power supply X rays at the very least.

You can see where I turned off the fusor at around 350 seconds, and took quite awhile to get the silver to the geiger to see how hot it got. Extrapolating back - about 1700 cpm for this run. That seems about right, as if the new oven works just about the same as the last one - except this one doesn't melt and stink when the fusor gets hot. The water did get warm...that's about it. It might have gotten hotter if it had better thermal coupling to the tank. I also added a new source of cooling air (a modified APAP machine to really crank out the CFM at fairly big pressure drop) and that seemed good too, but will be a little stressed if we go to full power and don't have more cooling. We see in this, as well as most previous run plots, that fusion is initially higher due to things hitting D atoms buried in the stainless steel walls, and then drop as it gets baked out by heat. Not sure if some other material would hold it better, but for now, just want to keep things cool, and all the D absorbing materials I know of do let it go when things get much over boiling water temperatures anyway. At this point, coating the inside of the tank with something "light" as in Be or Ti would benefit us maily by preventing some of the high energy X rays - low Z stuff will do that for ya, since it can only make up to a certain energy in its K lines.

NewDetectorAndFanLocation.JPG
New stuff at the back end. More work required here, I just couldn't wait to test what I've already done, like move the neutron detector, new oven, fan and so on.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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