Calculating the Electric Field by applying a potential

Hello Everybody,

I want to simulate the following problem: I have a geometry (for simplicity assume it is e.g. a box) which is hollow (there is a vacuum inside), and the boundaries consist of some combination of slabs of materials with different thicknesses and widths (copper - stainless steel - copper - stainless steel - copper - etc). I want to apply an electric potential (e.g. 20 kV) at the lower left corner, and I want to have ground potential at the upper right corner. My questions are now:

1) Do I have to use the electric current-module? Because I have conductors I assume that some currents are flowing through the copper and stainless steel...
2) How can I visualize the Electric Field inside the vacuum?

What I did so far was (using the electric current-module) applying a terminal to the lower left corner and defining a potential (20kV), and defining ground on the upper right corner. For the vacuum I used Helium gas and set the electric conductivity to 10^-40. But my problem is that the electric potential behaves as if the helium gas was a conductive material, and thus the electric potential decreases linearly along the helium volume, independent of the conducting boundaries...

I appreciate any comments - thanks a lot! :)
Best regards,
Andreas