Can the tungsten electrodes be baked at a higher temperature outside of the chamber? They can be inspected for oxide levels before assembly and then everything can be microwave baked after assembly in the chamber. It is more work but better quality control.
I think that the problem is that tungsten oxidizes in air. You would have to bake it in an inert atmosphere and keep it in one until it is in the vacuum chamber. The assembly has parts that can’t be baked and assembly is to complicated to do in a glove box or similar device.
In a few months they should be switching to a beryllium electrode that won’t have as much of a problem with oxides.
Tungsten does oxidize in air and humidity but it happens well above room temperatures according to these links: Page 43, page 50 and Wikipedia links.
It should be possible to treat the tungsten in an external chamber at elevated temperatures and then cool it to room temperature before removing it from the chamber. Then assembly can proceed as normal with very little oxidation occurring. The microwave treatment of the assembled dpf can remove surface oxides and moisture from the parts.
Tungsten is a very complex material. The brittleness of the metal changes greatly depending on so many factors including temperature treatments and inclusions of nitrogen, carbon and oxygen in the sintered metal during manufacturing and machining. See this link: Physical properties
It would be good to test any treatments on samples of the leftover tungsten from the machining to shorten the new electrode.
Moving to beryllium electrodes makes sense with respect to reduced SXR attenuation and therefore reduced erosion, but the problem is going to shift to erosion of the electrodes by the high current filaments. I wonder if any thought has been given to plating the high risk SXR locations with beryllium. What kind of beryllium thickness is needed to protect any underlying layer? It seems that these electrodes are long lead time and very costly. Tungsten (maybe even 2% thoriated) is definitely the best best with respect to high current.