Tube with capillary electrodes

Since I still have difficulties making a side exhaust tube on my homemade discharge vessels, I decided to investigate some alternative methods and designs that would facilitate the tube filling, pumping, and seal off. One of them consists in using stainless steel capillaries instead of the usual dumet (or similar) wires for the glass-metal seals. However, stainless steel doesn't have suitable thermo-mechanical properties to form airtight seals with soda lime glass, so I wrapped each tube with a tight coil made with a very thin kanthal (Fe-Cr-Al alloy) wire, which acts as a strain relief. The trick worked and no cracks developed in the seals, and although it is certainly less clean that normal ones, it is surprisingly airtight and allowed me to do some plasma tests (see there).

The picture above shows the tube after those experiments, with the electrode chambers heavily coated with iron oxide as a result of sputtering and chemical reactions with oxygen from the air fill. The right side shows more deposits because of the negative bias of that electrode as a result of a greater sodium release (see description in the post linked above and notice the white altered glass zone where the electrode emerges from the seal). I eventually sealed the tube off by cutting and pressing the (left) steel capillary connected to the gas pumping setup. Then I found that the steel-kanthal seals are not entirely satisfactory as the pressure in the tube rose very slowly. So, it's back to square one for me. That was still a nice experiment in my opinion.