Time flies, it's been a month and a half since I posted a progress report, I have been busy with other things, but I also had to wait a long time for the final parts to get finished.
After putting a lot of pressure on the engineer I finally received the last two critical parts for the stack last week. The custom made vacuum duct made from 50 mm stainless steel pipe is TIG welded to an ISO100 blank and fits onto the Varian turbo pump, it has two NW25 nipples which will connect to either end of the chamber. I gave it a bit of a polish to make it look a bit sexy.
- 50 mm Vacuum Duct with ISO100 Flange to NW25
I blanked off the NW 25 ends and pulled a vacuum to see if the tube had any obvious leaks and it appeared to hold vacuum pretty well, after a 20 minute pump down to 1 micron I turned off the valves and left it over night, the pressure had risen to 2000 micron, but considering it was the first pump down and a very small chamber (only the tube) I think that's okay.
- Vacuum gauge after 24 hours.
Then came the difficult work of preparing and gluing the stack together. preparation has taken me weeks. Each aluminium disc has been ground against the matching class disk with 50 micron aluminium oxide to produce a flat surface, this is essential to achieve a good seal.
With all the discs prepared and cleaned with acetone I set aside all day Sunday to glue the stack together, it was challenging to say the least. The trick is to keep everything 100% clean and apply exactly the right amount of glue without making a mess (easier said than done).
I found the best way to apply the latex glue was with a plastic squeeze bottle with a nozzle, applying a thing bead around the ring 2/3 from the centre, then carefully place one disc at the time onto the glue and allow the capillary effect to draw the glue across the disk. Too little glue and the gap wont fill and too much glue and it will run into the chamber.
Fortunately I designed the discs with a small lip towards the chamber which prevented excess glue running into the chamber. As can be seen from the photo some glue overflow on the outside is obvious, but this wont be a problem as the glue remains between the glass discs, and in any case it is not conductive when dry.
It wasn't necessary to clamp the stack, as is extremely heavy and gravity is more than enough to keep it clamped, the middle chamber which is a 6" hollow sphere machined from a solid stainless steel bar weighs at least 25 kg.
The end caps with the NW25 fittings are machined from solid aluminium and will be at ground potential during operation.
Slightly above center on the reaction chamber a small 1/8" Swagelok fitting can be seen, this is where the Deuterium gas supply will enter the chamber.
I expect it might take a couple of weeks before the latex has dried up to a point where I can pull a vacuum on this chamber, and then it might take another couple of weeks before all the water has been pulled out. As it is winter here now, and fairly wet and cold, I might get a small heater to speed up the process.
Once I pull a vacuum on this chamber I will back fill the chamber with argon and do some plasma cleaning of the chamber to get out any impurities.
So far I am reasonably pleased with how it's all coming together, but still some way to go.
- Double ended stack after gluing
Here is an image of the 6" chamber before it was welded together, it wasn't cheap.
- 6" Chamber
Thanks for reading...