Hey Joe,
It was an Adixen 2-stage, rotary vane. That one should've had a anti-suckback system, but I'm not sure if it malfunctioned or a purge gas was the culprit. God only knows how many hours that pump's oil had on it before I changed it.
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High Voltage
The high voltage is supplied by a 125kVp 300mA oil-tanked X-ray transformer. This I removed the filament transformers from, and subsequently dropped in a 75kohm ballast resistor (brown ceramic coated). It is then ran to a Machlett HV-1 voltage divider for measurement. Next, it goes to the HV feedthrough I made.
At the moment, I am also running a shorted MOT "inductor" in series with my transformer primary to keep everything on a tight leash while testing. Once I finish sorting out a few problems, I will swap it out to a real inductor from a MIG welder. If that goes well, I'll take it off too.
For current measurements, I am using a 10ohm 7w 1% wire wound resistor from both center taps to the ground. The ground is ran from the cable to the star-ground on the back of the control unit. That is then connected via two 8ga copper cables to the shell where everything on the frame is star grounded. (Two cables were used for redundancy incase a ring connector or something failed.)
I've done some work to the feed-though since it's use in Fusor-V1. I have beveled the edges internally and swapped to button headed bolts on the flange. I also opted to swap to a BNC connector for attaching the cable since it can be rotated but can't be pulled out. I then added some white silicone and a glass cylinder to it, just to be extra safe.
I'll talk more about shielding and thermals lower in this post, but something had to be done for both at the feed-through. To efficiently shield the x-rays, I wanted to get the lead sheet closer, but high voltage is the caveat here. So anyways, I had a styrene-acrylonitrile water filter housing, and decided to use it. (The breakdown voltage is 12-24kv/mm for SAN.) I cut some holes into the bottom of it and attached a PVC "T". On one side, I fed in the HV cable, and on the other, I attached a fan for cooling. The filter sits perfectly on the button headed bolts, creating an even gap around the entire flange.
Shielding
Shielding in this system is a necessity. X-Rays were rough at higher voltages. Most of the lead I used was from an X-ray film cabinet. They are entirely lined with 1mm sheet.
First thing was the viewport. I had always used a camera for Fusor-V1, but I finally I found some leaded glass: 1.6mm lead equivalency at 150kv. However, with horizontal mounting the scatter was pretty bad. Much of this is remedied by rolling a lead cylinder that fits closely with the glass.
Next up was the feed-through. I wrapped the SAN housing with 2mm, and made a 1mm skirt to cover the air vents at the bolt holes. After that, the body got wrapped with 2mm and the other parts of the same thickness received 1mm.
All good,
right? No. The massive ISO160 currently uses an aluminum centering ring and a Viton O-ring. After a little thought, I found some pipe solder that would fit in the gap like an external ring. Two layers remained flush, and greatly reduced the rate. I had an excess of it, so I just wrapped it until I ran out. Later on I added a ring of the sheet stuff around the clamps to reduce it even more.
For the most part, all of that works great. The bottom of the ion gauge and back of the TC can put out at higher voltages, but it's not too concerning for the moment. I followed all of the lead up with some aluminum tape with a 300*F (149*C) max temperature.
Thermals
For now, I've been running under ~1kw, and haven't really soaked the grid with anything more than ~30 mA. Even then, it gets hot after a bit. I am currently limited by the big ISO flange and the Aluminum tape (180*C, 149*C). Initially I planned to water cool Fusor-V1, but we saw how that worked out... Anyways, I had already made a nice heat exchanger and reservoir. I don't plan to leave them there for looks. I will be adding something in the future hopefully. For now I just slapped on a truck temperature gauge to be conscious. Soon I'll add some thermocouples and more fans too.
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-Luke Harrill