Connection for tungsten heater
A simple pair of copper busbars (0.5 * 0.125) with a high pressure contact would appear to be all you need for each terminal. 
Separate your wires where they enter the busbar area and clamp each wire individually with a stainless steel screw and high pressure domed washer. 



Separating the Tungsten wires may help in supporting your crucible.
If you are in a vacuum chamber you can connect your entry wire to one of the busbars, I doubt you need to do both at the low current you are using (20A).