Would it be possible for you to explain the evacuated tube process? I am interested in making a solar oven.
Vacuum tubes are made from 1/2" inside diameter glass tubing. The tube elements are connected to the outside world with small wires that pass through the glass. The top of the glass tube is stretched to a small diameter and then hooked to a vacuum pump that can pull a really hard vacuum. An oil diffusion pump is typically used for that.
I am not sure how that will help with a solar oven. Tell me more, maybe it can. I can also link you to sites related to vacuum tube construction.