The growth rate of EHD instabilities induced by unipolar injection

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