THE BEHAVIOR OF SMALL BUBBLES GENERATED BY ELECTRICAL-CURRENT IMPULSES OVER A WIDE-RANGE OF APPLIED PRESSURES

Very small bubbles are generated in chemically different insulating li quids in a repeatable and controlled way. A constant de voltage is app lied between a sharp point and a plane electrode. Above a threshold vo ltage, the current is ''impulsional.'' The origin of each impulse is a n electron avalanche while the consequence is the formation of a small bubble at the point electrode. The relationship between the injected electrical energy and the maximum bubble size is examined. Depending o n the liquid used, and therefore the level of energy injected, differe nt behaviors were observed. In particular, results for very low energy injections were explained by mechanical rather than thermal processes . The nonequilibrium plasma formed following an electron avalanche, br ings about the emission of a pressure transient, behind which there is an ''afterflow'' of matter. The liquid travelling outwards from this point source causes the liquid to break down mechanically, thus formin g an almost empty cavity, which disappears on collapse. In the case of high energy injection, energy is lost to local heating of the liquid. (C) 1996 American Institute of Physics.