The document discusses high voltage engineering, specifically focusing on Townsend's ionization coefficients related to gas breakdown. It explains ionizing collisions that create positive ions and electrons, and distinguishes between primary (α) and secondary (γ) ionization coefficients, outlining the processes that lead to gas breakdown. Additionally, it highlights the factors affecting these coefficients and their dependence on gas pressure.

1. HIGH VOLTAGE
ENGINEERING
 TOWNSEND’S
IONIZATION
COEFFICIENT
IN SIMPLE
LAUNGUAGE
LEC # 05
BREAKDOWN
IN GASES

2.  When one electron collides with a neutral particle, a positive ion and an
electron are formed. This is called an ionizing collision.
 Assume n0 is electrons emitted from cathode. Let α be the average number
of ionizing collisions made by an electron per cm travel in the direction of the
field where it depends on gas pressure (P) and E/P, and is called the
Townsend’s first ionization coefficient or primary ionization coefficient.
 x is a distance from cathode and nx is number of electrons.When these nx
electrons travel a further distance of dx they give rise to (α nx dx)Electrons.
TOWNSEND’S PRIMARY IONIZATION COEFFICIENT

3. TOWNSEND’S SECONDARY IONIZATION COEFFICIENT
 The electrons produced by these processes are called secondary
electrons. The secondary ionization coefficient is γ.
 Once Townsend’s primary ionization is initiated secondary ionization
processes follow resulting in the final breakdown of gases.
 These processes are :
 Ionization due to positive ions.
 Photo ionization
 Liberation of electrons from cathode due to positive ions
bombardment.
 The metastable particles may diffuse back causing electron emission

4. TOWNSEND’S SECONDARY IONIZATION COEFFICIENT
 The net number of secondary electrons
produced per incident positive ion,
photon, metastable particle, and the total
value of γ is the sum of the individual
coefficients due to the three different
processes, i.e., γ= γ1+ γ2 + γ3.
 γ is called the Townsend's secondary
ionization coefficient and is a function of
the gas pressure p and E/p.

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