We want to down size the size of the view port windows so we can have a higher quality IBS AR coated windows and also lower the surface area of fused silica. Fused silica has a relativlty high emissivity at far IR wavelengths at about ~0.75, this will lead to stronger coupling to the lab temperature variations.
Rana has suggested maybe a cone shaped end cap: https://goo.gl/photos/QfRoyrRAczHSjbpr5 . This comes to a point where a conflat mountable assembly with a small window could be fitted. We could also use a flat plate and attach a window to that. This seems like it would easier to manufacture.
After talking to people, it turns out the cryo people are planning on making their own (Johannas is supposed be drafting something like this I think). We should probably try to have one standard size between experiments to save work.
Before talking to cryo people, I had drafted up a simple assembly (attached below) that would make use of the following off the shelf parts: