How to make the particles visible only on the outside of the circle


I created an emitter in the center of the circle. But I don’t want the particles to be visible inside the circle, only outside it. Particulars must fly exactly from the center of the circle.
How can I realize this (without masks)?

    alpha: {
        onUpdate: (p) => (Phaser.Math.Distance.Between(p.x, p.y, CX, CY) > RADIUS ? 1 : 0)