I want all particles that I emitted to settle down on a circle shape after animating them in space. What would be perfect is to be able to draw a circle shape which works as a particle attractor after a certain time.
I would recommend you use a different plugin, use the shatter plugin.
Follow the steps in this tutorial
This will let you break apart your circle into particles. Then when done the composition, simply pre-comp the layer and use the time/time-reverse layer to let the particles come into a circle.
While it seems a little backwards(literally) to do it this way, I think this is the best way to accomplish what you are trying to do.
You won't be able to get a particle attractor or other advanced functions like that unless you are working in cinema 4d or other 3 rendering software.