For cathode aging, a polymer formation deposits on the cathode surfaces. This insulating layer prevents the neutralization of positive ions, leading to the formation of a surface charge. The charge induces a high electric field which can be enhanced enough to extract electrons from the cathode. Most of them recombine with positive ions immediately, but some of them drift to the anode and generate avalanches at the sense wire. The avalanche positive ions come back to the cathode, enhance the electric field of the insulating layer, and thus feed a continuous, self-sustaining local discharge in the chamber without external irradiation. This effect is called the Malter effect...