Fascinating, how did you make this..?

As I said on one of Max's pictures, I just love these experiments.! We're lucky to have you as members of the site.!

Ria, I bought some electrodes and glass tubing from a neon supplier during 'lock-down'. I have a vacuum pump and I think I filled this one with argon welding gas. Not ideal as it isn't pure but still works ok. The glass is just workable with a butane blow torch. As for the high voltage side that's easy.

Awe, thanks Sammi, I just love doing experiments, perhaps too much.

We'll have to come and visit one day, and hopefully you can get here as well sometime

Really neat experiment. At what pressure did you fill the tube?

Thanks. Good question Max, but to he honest I can't be sure. When making these I was having a bit of an issue with leaks and I would vacuum down to around 0.1 Torr and bombard and then fill to about 0.2 torr and seal off quickly. Generally it could be 0.6Torr by the time it was sealed. I quite often ended up with too low a pressure and the electrode sputter quickly with the rise in voltage and further gas absorption in the sputter coating.

0.6 Torr is rather low for the argon fill, and it explains why you have such nice "sausage" striations in your discharge. That effect is caused by the periodic modulation of the electron energy in the positive column, and this can be achieved only in conditions where there is limited electron-atom collisions in the plasma. Such striation gets destroyed at higher gas pressures as a result of the "randomization" of the electron motions due to a critically high collision frequency (we can see those collisions as the scattering of electrons, especially at low electron energies resulting only in elastic interactions with atoms).

Excellent information.!

Max , I suspected this has to tie in with the frequency of the supply applied too, hence tuneable by loading. I think the driver was over 20kHz here.

True, the supply frequency is what causes those striations in the first place, but for this to happen electrons in the discharge must not be scattered to much by background atoms or the spatial modulation of the electron energy will lose its coherence.