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The results are presented of a study on the influence of back corona on the performance of a laboratory scale wire-plate precipitator, with the plate to plate spacing as a parameter. Back corona is introduced into the precipitator by increasing the ash resistivity, attained by increasing the ash-laden gas temperature from 21 Â° C (a no back discharge condition) to 104 Â° C. Performance is evaluated in terms of the Deutsch migration velocity and using the particle concentration measurements made at the inlet and outlet of the precipitator with an optical counter. Results for the four different plate spacings with no back discharge show a time-independent migration velocity and current density, with higher migration velocities for the wider plate spacings. Results with back discharge show an initially rapid decrease in migration velocity with time, accompanied by a rapid increase in the current density, with greater decreases for the wider plate spacings. The behavior of the precipitator with and without back discharge is consistent with the space charge model interpretation of the wide-plate spacing precipitator.