Oh, this is inspiring, I must get back into glass work. I became a bit discouraged with glass to metal seals failures and haven’t been playing with it of late. I don’t think the major issue was the metal glass compatibility but the working temperatures I can achieve with propane and air being just at the minimum working temperature for glass. I also had numerous issues with sputtered electrodes creating getters and mopping the gas pressures until the discharge would be faint or difficult to strike. Pushing the voltage tended to turn tubes into x-ray emitting devices. Most of my disasters didn’t have glowing electrodes but the large neon style electrodes sputter nicely with high-speed impact and dissipate the heat well. The current doesn’t need to be high at these voltages. A quick power calculation shows just how high-power dissipation can be. A current of 25mA in a medical X-ray tube is likely to see over 3.5kW dissipating at a spot on the anode. Most large X-ray tubes used fast rotating anodes and still show a large amount of surface damage with use.

Are we about to see a 'Battle of the Engineers' to see who can come up with the most awesome picture...

There's no need to go into battle when we share a common interest and there's plenty for two, Sammi

Tuopeek - Despite its intrinsic challenges and difficulties I do find glass working to be a very rewarding activity, especially when combined with electricity and vacuum/gases. I can imagine the sense of wonder Crookes and Geissler must have felt when they made and ran their discharge tubes. I've also struggled with glass-metal seals and I agree with you that finding the right materials was not the biggest problem. What made the difference for me is the annealing step after I make a feedthrough (I use a broad oxygen-poor butane-propane mix flame for that). Adding that to my workflow changed everything (I work with soft soda-lime glass, which is particularly difficult given its high thermal expansion coefficient). The problem of gas cleanup is not so easily resolved though, especially with molecular gases... Daniel McFarland Moore certainly had to deal with that with his nitrogen and carbon dioxide tubes in the days before the fluorescent tube! If you don't want to (or can't) work at very low current, like in spectroscopic tubes, then there is no other way than to have a gas reservoir attached to the lamp if it is to be run for any extender period of time. This also applies to certain noble-gas lamps when an extremely long service life is needed, such as in this particular case.

Indeed, it must have been truly amazing during the early times of discover. The popularity and complexity of early Geissler tube certainly supports this fascination too. Even today there is a strong interest with it in plasma globes and inductively powered toroidal discharges.

I have an old Crookes type X-ray tube. These all had clever gas reservoirs to set pressures and hence the operating voltage for the tube. It’s also interesting to note the size and construction of CO2 laser tubes with only a thin central tube for the active discharge.

@Max I was meaning each of you trying to outdo the other in superlative images.!

I understood what you meant, Sammi, and I assure you that it's not a competition. We're just posting about what we enjoy doing and collecting, there's no intention to outdo the other here

By the way, yesterday I managed to make my first vacuum incandescent lamp, but tungsten transport via the water cycle was particularly strong and resulted in severe blackening (despite that I baked and degassed the lamp thoroughly before I sealed it off). I'll look into gettering methods, including with the use of electrical discharges, maybe I can get rid of the residual water vapor and hydrogen via plasma molecular dissociation.



Tuopeek - Sealed CO2 lasers are certainly very interesting. If I remember correctly, those have some sort of catalytic regeneration of the carbon dioxide.

@Sammi - It’s not rivalry, it’s idea exchange and discussion. You’d be amazed how much this helps understanding and innovation.

@Max - I think early CO2 lasers required a feed of fresh gas due to decomposition in the discharge. A catalyst would be a better cost option. I will have a look at the tube I have. Don’t remember seeing a catalyst but it has a large reservoir for gas and a convoluted route for it to circulate. Perhaps surprisingly CO2 is not the main gas, helium is and I think it job is mostly heat transport. Nitrogen is also part of the tube mixture.

Nice filament lamp by the way. I haven’t tried that, other than to form hot cathodes in other experiments. Is the vacuum not always going to be your enemy with filament evaporation? Have wondered if a simple getter and air filled would work with only a partial or minimum vacuum, although not efficiently.

And we like to see it,!

Glad to see that we are on the same page

Tuopeek - Tungsten evaporation will always be an issue in vacuum and at very low pressures. So, provided that I have everything else under control (i.e., oxygen and water vapor impurities), it's only a matter of operating the filament at the most suitable temperature. On the other hand, blackening from metallic evaporation (and sputtering) may not be that big of a problem in long discharge tubes if it's localized around the filament... will see, I need to do some tests to judge the severity of this issue.

About CO2 lasers, it's correct that the gas fill consists of a He-N2-CO2 mixture. Nitrogen and helium forms a Penning mixture which is useful to ensure a homogeneous discharge, especially at higher pressures such as in TEA lasers, while nitrogen stores energy from the discharge and transfers it to CO2 molecules via resonant collisions. That's a very well thought out system indeed!