The growth rate of EHD instabilities induced by unipolar injection

摘要

Transient electrohydrodynamic instabilities in liquid dielectricshave been studied by using an electron beam as an injecting contact. Aprimary beam injects a uniform pulse of charge into the free surface ofthe liquid film, and a second beam, directed across the liquid surface,monitors the surface potential of the sample. The pulse charging methodof measurement used in these experiments has several advantages over theconstant current method: (i) the onset of EHD instability is welldefined; (ii) charge decay at injection levels below the instabilityonset provides a measure of the negative ion mobility in the fluid;(iii) the growth rate of the instability can be measured. Above the EHDinstability onset, for a short time after the charging pulse the decayfollows the SCL model, but after a time delay the decay rate increasesas convective motion sets in and enhances the rate of charge decay. Fromthe charge dependence of charge decay we can deduce the field dependenceof the growth rate