change individual particles's velocity via script

Trail.cs

using UnityEngine;

public class Trail : MonoBehaviour {
    ParticleSystem system;
    public Transform anchor;
    private Vector3 anchorPosition;

    private void Awake()
    {
        system = GetComponent<ParticleSystem>();
    }

    private void Update()
    {
        anchorPosition = anchor.transform.position;

        var particles = new ParticleSystem.Particle[system.particleCount];
        int particleCount = system.GetParticles(particles);

        for (int i = 0; i < particleCount; i++)
        {
            var centerToThis = particles[i].position - anchorPosition;
            particles[i].velocity = centerToThis.normalized * 100;
        }

        system.SetParticles(particles, particleCount);
    }
}

ParticleSystem.MainModule.simulationSpace must be World.