At one end of the cylinder is the radioactive sodium, busily emitting positrons.

ECONOMIST: Antimatter

When they hit the electric field at the end of the cylinder, they bounce off it, spiral back towards the entrance, where they run into matter, and annihilate.

ECONOMIST: Antimatter

As the particles enter the trap, the magnetic field forces them to travel in spiral orbits so that they cannot crash into the walls of the cylinder, and a strong electric field plugs up the far end, corking up that route of escape.

ECONOMIST: Antimatter