How hot do the temperatures on the top and bottom of the fus

[Andrew Seltzman]

For your intrest on casting vacuum chambers, it can be done and done well. The toroidal vacuum chamber for MST at UW madison is cast aluminum, and we get vacuums in the 1E-7 to 1E-8 torr range. Recently the madison plasma dynamo was constructed out of a 9 foot diameter cast aluminum sphere.

http://plasma.physics.wisc.edu/mpdx
http://www.news.wisc.edu/newsphotos/dynamo11.html

For a fusor, just buy a stainless hemisphere though.

[Rich Feldman]

Very nice, Andrew, thanks for sharing. Quite the molding project for a one-off part. Biggest core I've ever seen. I wonder what alloy was used?

I bet that success with the smaller chamber helped to get approval for the 3-meter one.

As for why not a stainless steel weldment, do you know if magnetic field perturbations were a consideration?
Long ago I worked on the magnetometer boom for Voyager spacecraft.
Even "nonmagnetic" stainless steel can develop unwanted magnetic permeability
from cold working and welding, and it would not be cheap to anneal a 3 meter hemisphere.
http://www.cartech.com/techarticles.aspx?id=1476