ParticleSystem.MainModule.loop

Description

Specifies whether the Particle System is looping.

If you disable looping on a playing Particle System, it stops at the end of the current loop.

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(ParticleSystem))]
public class ExampleClass : MonoBehaviour
{
    private ParticleSystem ps;

    void Start()
    {
        ps = GetComponent<ParticleSystem>();

        var main = ps.main;
        main.loop = true;
    }
}