The Catapult field (Lorentz Force) - seeing the field

The current in the long wire is up out of the page, making an anticlockwise magnetic field around it. The permanent magnets have a field right to left. When you combine the two fields, they vector-sum to form 'the catapult field' that produces the Lorentz Force - the long wire is pushed towards the bottom of the screen (and the magnets pushed up by Newton's Third Law).