Variation of Townsend's Second Coefficient in Electrodeless Discharge

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Abstract
The variation of γ, the second Townsend coefficient, in an electrodeless discharge has been studied in air with discharge tubes of different lengths within the pressure range of 1 μ to 1000 μ. It is found that γ varies with pressure and also with E/p as in the case of d.c. discharge. The graph of γ against E/p shows that γ is large for both low and high pressures and remains constant over a certain region of pressure near the value for minimum breakdown voltage. It is assumed that in the case of electrodeless discharge, and within the range of pressure used in the experiment, contributions to γ arise from four distinct causes: electrons striking the glass surface, positive ions striking the glass surface, ionization by positive ions, and photo-ionization. A mathematical expression has been derived for the variation of γ with E/p; this agrees well with experimental results.

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