steve’s remark on pre-comp is probably what you need right now.
some other quick tips:
set emiiiter>velocity to 0 (so particles stay still)
then use Physics>Air>Turbulence>Position – keyframe from high value at time 0 and then down to 0 (now they form the 7) and then high up again (they spread apart again).
then add velocity or wind to taste.
Peder Norrby / Trapcode