I have a particle system using a dupli group as the particles and the volume of a UV sphere as the emitter. I would like to place an object in the center of the emitter and make it look as if the particles "explode" from this object. This means that the concentration of particles should be much higher in the middle of the emitter than around the perimeter. Using the volume of the UV sphere as an emitter already has a bit of this effect, but not extreme enough. I am modeling a static scene, no animation intended.
I tried using a force field but this does not seem to do anything, even when cranking up the strength (as in Blender 2.78a force field not affecting particles). Or is this only for animated scenes? How do I achieve the desired effect? I feel it must be quite simple but I just can't find an answer anywhere.
(I am very new to particle systems and force fields. I could not find any helpful tutorials, if you know of any, please point me to them.) Here's the .blend file: