[MadnessASAP]

You don't need a significant flow of argon, just enough to keep unwanted gasses out of the waveguide.

It's possible there exists a material that is transparent to mm waves, airtight, and can survive the conditions at the bottom of the hole. In such a case they could cap the waveguide and prevent any gas leakage.

I'm quite sure Quaise is well aware that Argon isn't cheap and are already exploring multiple avenues for reducing its usage.

It is interesting that they have to use Argon instead of the more typical Nitrogen or SF6. A waveguide with such a significant pressure differential is decidedly unusual and a unique challenger for what they are doing.

[pfdietz]

SF6 is a horrifically powerful greenhouse gas, so I doubt it could be used. Its GWP is somewhere around 23,000 on a 100 year timescale.

[MadnessASAP]

Oh yeah, there's no shortage of reasons not to use SF6. Even in conventional waveguides, as far as I know most designs these days prefer nitrogen or dried atmospheric air.