High Voltage plasma cleaning.

I was wondering if it was possible to have high voltage plasma in a conductive vacuum chamber?
Seems like it is!
My previous high voltage stuff had been in the glass belljar of previous posts.
So when I started reading about plasma cleaning and surface modification, it got me wondering. 
Here is the video: 


If you are still reading, some details are: The vacuum feedthrough is a 4mm brass rod through a 7mm glass tube. Soda glass I think. Not boro' anyway. Then the threaded bit is from an old lamp fitting. I did a little work on the lathe to make the o-ring groove. All sealed up with normal(not Kwik) JB Weld.

Then it gets pushed through one of the existing electrode holes in my base plate. I know the chamber is filthy...
Strangely, I got the best ever vacuum level from my mechanical pump on this test. I got down to nearly 2x10-2( chamber pressure) normally I only get 6 or 5x10-2. Just at the edge of diffusion pump land.

 

Some strange thing that happened were... 

Initally the pressure began to rise when I turned on the NST and so plasma. I'd unplug and let the pressure drop again. I did this about 5 times until gradually, the pressure stopped rising. Then I was able to leave the NST on for about 5mins or more. I didn't want to over heat the electrode.

Total in plasma was probably 10 mins at 150 watts.

In the video is some poor footage of the plasma exposed surface of some acrylic and the unexposed(I peeled the plastic film back after I took it out of the chamber). One wetting well, the other, no way!

As I handled it, the grease from my fingers was busily spreading from the sides of the acrylic across the surface. It was very interesting to see the contamination spread.

 Also possibly there was a good bit of oil from the saw blade used to cut this bit of acrylic.
The other sample in the chamber was a piece of fast cast polyurethane resin. It work on that too. Over all effect seems short lived. Maybe straight under Di-water is the thing to do.

Conclusion: yes it works. 
To do: clean the pieces normally to remove most of the contaminants. Wear gloves.
Try...spontaneous bonding of very clean flat surfaces by contact.

Cheapo (metal) Bell Jar the beginnings...

After a long stretch of solid work I got a chance to get back to vacuum for a while.

I was getting a bit nervous of my glass belljar imploding so I decided to go for a metal one instead.

After seeing a guy on youtube who built a mildsteel box to coat telescope mirrors in I decided to give the gas cylinder a second try.

I bought a used gas cylinder 380mm diameter just right for my base plate at 400mm.

I let the remaining gas out and unscrewed the valve. Don't forget to fill it with water to displace the remaining gas before you go a cuttin'

 

I marked the line by wrapping a yoga at around the cylinder to get a parallel line. That wasnt a good idea... you need to use some thing not so stretchy, that defeats the purpose! I marked away and used the bottom end with the complete dome.

I put the cylinder on it side and cut it with the water still inside. It was pouring out all over the place. I trimmed much of the foot ring off too. I wanted to get rid of excess weight. It is heavy.

Once it was cut I dried it straight away. We don't want any rust forming, very bad for outgassing.
Then on to leveling. Even though I paid great attention to the cutting I still spent 3 hours leveling the cut to get it nice ond flat. For this process I spray glued strips of al'oxide paper to a scrap of countertop. Its nice and flat and very ridged. I did a couple of hours of 80grit and an hour with 120...

Very tiring on the arms! During the sanding I regularly ran a black marker along the edge so I could see my progress clearly. I would watch the colour sand off, and the black patches get smaller and smaller. Eventually I got down to a consistant edge. I went then, by hand with a finer sand paper to get rid of the 120 scratches. I rubbed along the edge insted of across it. If there are scratches left they are better not to be radial across the edge as it is more likely to leak in that case.

The whole interior had a dark crust on it. I don't know what it is, possibly passivated with phosphate? I diligentlly sanded this away. There was still a bad smell coming from the tank. This got less and less as the crustyness came off.
I cut a new flat rubber gasket and greased up and sure enough it pumped down to 40micron the limit of my pump....