You'll need three nulls.
Put one in the middle. This one will be spinning.
Put the other one as far outside as you need to get the size of circle you want. Parent it to the spinning one.
Apply the following expression to the third null: c = thisComp.layer("child");
c.toComp(c.anchor_point) (I think that's right.)
Replace the "child" part with the name of the parented null.
Then alt-click on the xy position of your Particular emitter.
Type [ then pickwhip to the x position of the third null.
Type comma then pickwip to the y position of the third null.
Alt-click on the z position of your Particular emitter and pickwhip it to the z position of the third null.
- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')
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