private void swap(int idx1, int idx2) {
        Particle p1 = particles[idx1];
        particles[idx1] = particles[idx2];
        particles[idx2] = p1;
    }
Kills the particle at the given index.

@param index The index of the particle to kill
@see #getParticles()
jme3-core/src/main/java/com/jme3/effect/ParticleEmitter.java