public void killAllParticles() {
        for (int i = 0; i < particles.length; ++i) {
            if (particles[i].life > 0) {
                this.freeParticle(i);
            }
        }
    }
Instantly kills all active particles, after this method is called, all
particles will be dead and no longer visible.
jme3-core/src/main/java/com/jme3/effect/ParticleEmitter.java