The gun emits a stream of high intensity electrons that can be a spot or rastered into ovals, circles, trapazoids, squares, etc. and can be varied in intensity and in focus. Focused below the joint surface will penetrate and focused above will either surface melt or heat - so can be used to smooth a surface or for diffusion welding.
The work is prepared with precision fitting joints (no filler metal used) and is chemically cleaned. The assemblies are manipulated inside of the chamber similar to a milling machine so they are rotated or fed under the beam at a feed speed suitable for the material and its heatsink mass.
The welds can be confined to a needle point high intensity beam that can penetrate and leave very little weld distortion. Welding massive parts to super thin section parts is an example of the work done - such as a 2" thick bar of 304 ss welded to a .005" sheet ss foil - they become one piece of ss.
Since it is like a 'melting stylus', logos and drawings can be melted into the surface of a piece of sheet stock. It's an interesting machine to work with...
The lab uses it to weld niobiom super conducting cavities for use in the accelerator. The niobium welds must be super pure on a molecular level with absolutely no contaminates. That's the reason for the high vacuum in the chamber - 7 E-5 torr - but it can go as low as 3 E-7 torr. That is low enough that even nitrogen is condensed in the cryo pump.
Bill C.