Townsend (unit)

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The Townsend (symbol Td) is a physical unit of the ratio E/N, where E is electric field and N is concentration of neutral particles. It is defined by the relation 1{{\rm {Td}}}=10^{{-17}}{\rm {V\cdot cm^{2}=10^{{-21}}{\rm {V\cdot m^{2}=1{\rm {zV\cdot m^{2}}}}}}}.

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 E/N. It means that increasing the electric field 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 also

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