Increase of the electric field in head-on collisions between negative and positive streamers

Head-on collisions between negative and positive streamer discharges have recently been suggested to be responsible for the production of high electric fields leading to X-rays emissions. Using a plasma fluid approach, we model head-on collisions between negative and positive streamers. We observe the occurrence of a very strong electric field at the location of the streamer collision. However, the enhancement of the field produces a strong increase in the electron density, which leads to a collapse of the field over only a few picoseconds. Using a Monte Carlo model, we have verified that this process is therefore not responsible for the acceleration of a significant number of electrons to energy >1keV. We conclude that no significant X-ray emission could be produced by the head-on encounter of nonthermal streamer discharges. Moreover, we quantify the optical emissions produced in the streamer collision.