Experiments with "streamers" (as in "plasma streamer") with varying parameters.
All particles emit from the center. They are initially pushed outwards, then a second vector takes over, accelerating them into opposite directions. This second force, however, is longitudinally modulated, resulting in stripes in the stream.
Near the center, the wavefronts interfere in such a way that a pulsation occurs, with varying frequency. (No such pulsation or frequency is defined in the code.)
Particles are attributed an individual lifespan. On expiration, they are reborn in the center. There they might be held back for a while, in order to produce sudden outbursts of large numbers of particles, thereby generating different shapes.