Particle Tracks

Pravir

I am doing DPM modeling. I want to inject group injection where I am giving number of particles injected and diameter and mass flow rate of particles. Now I want to inject my particles from a circular inlet( this inlet is on X-Z plane). The X value of circle ranges from -2.5 to 2.5. and Z ranges from -2.5 to 2.5. So radius R=2.5.

I want to inject the particles uniformly starting from the circumference of the circle(R=2.5) and coming all the way towards the centre in a circular pattern(i.e R=2.4 then R=2 then R=1 then R=0.5 the R=0). Please tell me what should I choose as the coordinates(X, Y, Z) of the first point and the last point in the group injection panel.