In 3d

Continuing that last thing , I found out that if you have a cube, the total of the distances to the 8 corners squared generates a spherical gradient much like the square made a circular one. So I thought my first attempt at designing a charge concentrator could look like this (sort of):

The cube is flooded with deuterium gas plasma and all the positively charged ions have less potential energy as they move towards the center. Hopefully with a high enough voltage you could get them to fuse.