Effective secondary emission coefficient for flat cathodes in a high pressure gas

In the theory of gas breakdown, an important role is played by the effective secondary emission coefficient (ESEC) {gamma}: the number of electrons leaving the cathode surface per one impinging ion. Since long ago, it has been known that at low E/p values (where E is the electric field and p is a gas pressure) the so defined {gamma} depends linearly on E/p, reaching a constant value only at high E/p. The mechanism responsible for this dependence was identified as a reflection of a part of the secondary electrons from the gas atoms back to the cathode surface and based on J.J. Thomson`s simple consideration L.B. Loeb proposed a qualitative expression describing such a behavior: {gamma} = {gamma}{sub i}[4{nu}{sub d}/({bar {nu}}{sub 0} + 4{nu}{sub d})] where {gamma}{sub i} is the vacuum value of the secondary emission coefficient, {bar {nu}}{sub 0} is the average speed of electrons just emitted from the cathode and {nu}{sub d} is the electron drift velocity.