particle system in circle

How to create a particle system where particles spawns as a circle.

Here are 2 ways:

1: You can use a 3D-modeling tool to define a mesh that only has vertices in a circle, then in Unity, import the mesh and assign it to be the target mesh of a Mesh Particle Emitter. That particle system will then only spawn particles in a circle.

2: You can add a Mesh Particle System to your scene, and leave the Mesh property of its emitter empty, then use the Emitter's Emit-method in a script to spawn the particles in a circular manner yourself, using very simple trigonometry in a loop, something like this:

Emitter = GetComponent<ParticleEmitter>();

Vector3 position;

for (int i = 0; i < 360; i++)
{
    position = new Vector3(10 * Mathf.Cos(Mathf.Deg2Rad * i), 10 * Mathf.Sin(Mathf.Deg2Rad * i), 0);
    Emitter.Emit(position, Vector3.zero, 1, 30, Color.red);
}

The above code emits 360 red particles with a lifespan of 30 seconds and a size of 1, in a circle of radius 10, parallel to the yz-plane, with a center in the coordinate system's origin.