Townsend (unit)

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The Townsend (symbol Td) is a physical unit of <math>E/N</math>, where <math>E</math> is electric field and <math>N</math> is concentration of neutral particles. It is defined by the relation <math>1 {\rm Td} = 10^{-17}\rm V\cdot cm^2</math>.

This unit is important in gas discharge physics, because the mean energy of electrons (and therefore many other properties of discharge) is a function of <math>E/N</math>. It means that increasing the electric intensity E by some factor q has the same consequences as lowering gas density N by factor q.

It is named after John Sealy Townsend (see other articles in this stub).