Important Definitions about Ionization
Q. Define Townsend’s first and second Ionization constant. How the condition for breakdown is obtained in a Townsend’s discharge ?
Primary Ionization
It is the process of liberation of free electrons from gas molecules with simultaneous production of positive ions due to collision with free electrons.
Townsend’s Primary Ionization coefficient
It is number of electrons liberated by an electron due to collision with neutral gas molecule in travelling unit distance in the direction of applied electric field.
Avalanche
It is the group of free electrons travelling from cathode to anode in the gas and is formed due to ionization process. If occurs due to electron multiplication in the gap after primary and secondary ionization. And can be delayed due to electron attachment process of electro negative gases.
Secondary Ionization
It is the process of liberation of free electrons from cathode surface by impact of positive ion, metastable or photons on cathode surface.
Townsend’s Secondary Ionization Coefficient
It is the number of electrons liberated from cathode surface due to impact of single positive ion, photon or metastable.