[Unity] Particle System - magnetic field

using UnityEngine;
 using System.Collections;

 public class ParticleAttractor : MonoBehaviour {

     [SerializeField]
     private Transform _attractorTransform;

     private ParticleSystem _particleSystem;
     private ParticleSystem.Particle[] _particles = new ParticleSystem.Particle[1000];

     public override void Start ()
     {
         _particleSystem = GetComponent<ParticleSystem> ();
     }

     public void LateUpdate()
     {
         if (particleSystem.isPlaying) {
             int length = _particleSystem.GetParticles (_particles);
             Vector3 attractorPosition = _attractorTransform.position;

             for (int i=0; i < length; i++) {
                     _particles [i].position = _particles [i].position + (attractorPosition - _particles [i].position) / (_particles [i].lifetime) * Time.deltaTime;
             }
             _particleSystem.SetParticles (_particles, length);
         }

     }
 }