Power upgrades

[KJNW]

Recently, we upgraded our high voltage system for 60KV operation. That precipitated an interesting series of challenges that resulted from increased radiation and heat. I recount our solutions here as I believe that they may be useful to those who are dealing with similar issues. We use a full castle shield which weighs almost a ton, and is raised and lowered onto the fusor platform with 4 electric camper jacks. The first thing we saw was that the seam between the full castle shield and our fusor platform began to leak X-ray. It was enough to be concerned, so we have created "safety belts", which are nothing more than 35 inch by 4 inch belts attached with Velcro to the seam. Another problem is that when the shield is down, you have a 30 inch box in which resides a fusion chamber you are pumping up to a kilowatt into, and therefore you are inevitably going to have a heat problem. We have adapted a Koolance kilowatt liquid cooling system to the fusion chamber, and initial testing this weekend has shown that this will indeed allow us to run indefinitely (if all other factors are ideal) without melting the 54 gallons of borated paraffin inside the shield. We still have some cleaning up to do, but we are back on line with healthy neutron output. I have also created a promotional video which is intended to focus on the purpose rather than the technology of our program. It is located here. http://youtu.be/KbeAcFy3ErM Enjoy.

[Steven Sesselmann]

Carl,

Excellent work on the shielding..., your fusor must be the best shielded fusor on the forum, and so it should be, working with those young students you definitely don't want any 60KV X-rays flying around the room.

As you have discovered, it only takes a couple of mm lead to stop 60 kV X-rays, but you need to cover all sides, these rays scatter off any hard surface and can get you from where you least expect.

Steven

[kcdodd]

Carl, do you have an experimental estimate of how much the shield attenuates the neutron flux?

[Richard Hull]

Fabulous work!

In my opinion, this is certainly the most elegant and protected system ever to appear here in these forums. It has been nursed along from a bell jar to a solid SS system and up in voltage to a level that can, if well shepherded, compete with the best here. I am sure that there is a significant sum tied up in this effort, but far more important is the time and dedication spent by all involved.

Note* The giant glass view port is now your limiting factor in many ways. It allows significant x-radiation out into the area. A solid blank off here would virtually elimenate all forward blasting x-rays. This will become far more important as voltages and fusion increases. I assume the diamond plate sheet cover is steel and not aluminum? If aluminum, it will effectively be no shield at all unless almost 1/2" thick or backed up internally by sheet lead. Since you are talking about it weighing a ton, I assume lead is used.

A 3/4" or 1" clear aperture view port on the rear cover plate with a $50.00 small board camera with lens pressed against the glass would allow a small TV or a giant 56" plasma screen to be connected. This would then let you and a large audience look into the eye of the Gorgon remotely and safely.

Richard Hull

[Frank Sanns]

Very nice indeed. I always thought the best configuration would be to submerge the entire fusor except for the feed through in a tank of water. This would provide all shielding and cooling necessary. A two mirror periscope could provide safe live viewing even at the highest of powers.

Frank Sanns

[Doug Coulter]

We wrapped almost our entire tank in lead sheet early on to cut X rays, except for one deliberate hole for measuring the X ray output. The doggone things scatter off air, metal, etc even from many feet away - they wind up lower in energy, but...

Then we used a very compact portable geiger sensor and found all our leaks, We'd forgotten the bellows tube that connects the turbo on the bottom and were getting hammered right at waist level from that and had to add yet more lead. Let me suggest you do that too.

That still doesn't get them all. Neutrons captured in H give off 2.2 MeV gammas, or thereabouts, and in Boron, something less - but still a ton hotter than the power supply. Even you don't have enough shielding to stop those.

We're getting ready to run a test with a gamma spectrometer to see just how much of that is going on here, it should be interesting. I tried for a short time with just a scope. Calibrated so that 662kev gammas from a Cs-137 source were just one div pulses - we saw ~ 4 div pulses (Lots!) when the fusor was running...you don't want to do this for long, as you can activate your gamma spec head...

[KJNW]

We have been wondering the same thing , but as Doug Coulter points out further down this thread, the collateral radiation can make identifying that particular data point a little dicey. That's why we pursued an independent neutron source (which has now arrived) and I am hopping I can stage some comparisons later this week so I can at least speak in relative percentages regarding the attenuation of our shield. I will respond to this thread again once we have the data in hand.

[KJNW]

Thank you, Richard, and as you know this has been a team effort. Special thanks goes to David Housley, Robert Tubbs, and Jake Hecla for their assistance in design and fabrication as well as the power of prayer which kept me alive through 3 "en-lightening" events (which also smoked 5 $26 diodes and 1 $130 capacitor).
I want to pass on an important learning from this. Our full wave Cockcroft-Walton sits in a custom made acrylic tank with a 1 inch air gap above 5 gallons of Shell Diala AX transformer oil, and the leads from the diode array terminate on connectors within the tank air gap. You can also see our 100K ballast resistors in the picture below. Over time, ozone accumulated from corona on these connectors and saturated the air gap, thus creating a breakdown of the dielectric value of the trapped air. We kept hearing these explosions, but couldn't find the point to point path of the arc. During the last event, I was looking in the right direction and was able to determine exactly where the "bang" came from. The lid of the acrylic tank was acting as a diaphragm and transmitting the sound everywhere. David has a retrofit project to solve this problem, but for now we removed the main HV connector, and are passing the HV line directly to the submerged diode array.

[Steven Sesselmann]

Doug,

With a small NaI detector you should be able to see the 478 Kev gamma from the n + B10 reaction, but to see the 2.2 Mev gamma from H you would need a 2" or 3" detector in order to absorb the energy.

It will be interesting to see what you get.

Steven

[Doug Coulter]

I used the little guy in the pic below for my original test, and plan to use the big one for the real deal, but only after I cobble up a real MCA again. Either one produces pulse rates far in excess of what PRA can handle. I don't think scope screen shots will convince this crowd - but hey, if it comes off a computer, it must be true, right? At any rate, I want better myself, as I suspect there will be a few fun to explain lines from other things as well.