Complex sentence: On the other hand, electrons initiating the avalanches in the positive corona are produced by photoionization of the gas surrounding the high voltage anode with photons emitted in secondary processes in the more active region of the anode vicinity.
Split into simpler sentences: On the other hand, electrons initiating the avalanches in the positive corona are produced by the photoionization of the gas, surrounding the high voltage anode. The photons are emitted in the more active region of the anode vicinity.