A metal block, immersed in the electric field of an electrode, has been used to study the electrostatic discharge phenomenon. Using a highhyphen;speed transient oscilloscope, current wave forms of air discharge across a small fixed gap between the metal block and a current probe have been measured. The combined bandwidth of the measurement setup, including the oscilloscope, cables, connectors, splitter, and the probe, is above 3.5 GHz. The setup is capable of measuring rise time as fast as 100 ps. Voltage change on the metal block was also measured by a lowhyphen;speed transient oscilloscope. For a gap of 0.01 cm and a voltage of 1086 V, the observed current wave form of the discharge exhibits a rise time of 300 ps, a peak current of 5.8 A, and a pulse width at halfhyphen;height of 770 ps, about 2.6 times the rise time. The existence of a residual voltage on the metal block after each discharge was also observed. Using the Townsendrsquo;s agr; coefficient for the electron multiplication in air, an analytic model and a onehyphen;dimensional numerical model have been developed to explain the wavehyphen;form characteristics and the residual voltage observed.
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