Spontaneous branching of negative streamers

Summary form only given, as follows. Non-ionized media subject to strong electric fields can become ionized by penetrating streamers: rapidly extending space charge dominated, nonlinear structures. We study negative streamers in homogeneous fields in a simple mean field approximation for the reaction-drift-diffusion process. In our simulations, we observe that for sufficiently large fields. the streamer tip can split spontaneously. We discuss that this happens at a certain stage in which the streamer becomes susceptible to a Laplacian instability quite like viscous fingers. For further analytical progress, our stability analysis of ionization fronts identifies the screening length as a regularization mechanism. We also discuss experiments and compare with stochastic dielectric breakdown models.