Model of high-current breakdown from cathode field emission in aged wire chambers

Observing single electron pulses provides insight into the mechanism that leads to sudden high-current jumps (breakdown) in aged wire chambers. This single electron activity is found to be consistent with the Fowler–Nordheim (FN) equation for field emission of electrons from a cathode surface in a high electric field. The high electric field arises from the positive ion buildup on a very thin insulating layer on the cathode surface. A model is presented to explain the transient behavior of single electron pulses in response to abrupt changes in chamber ionization, as well as the steady-state rate during a long-term aging run. The model is based on properties of the insulating layer (dielectric constant, conductivity, and hole-mobility) as well as the FN equation. This model also applies to other avalanche type chambers such as microstrip gas chambers and gas electron multipliers.