Thresholds for microbubble and microplasma generation in liquid

Thresholds for low density regions (microbubbles) and microplasma light emissions generation in liquid are studied. With nanosecond microdischarges at different applied peak voltages with the different sizes of microelectrode tip, the low density regions (microbubbles) are captured by a high speed ICCD camera and the microplasmas light emissions are detected by both the ICCD camera and a Photomultiplier Tube (PMT). Deionized water with NaCl was employed as the experimental liquid. Different concentrations of NaCl present different conductivities. With the high conductivity (17600μS/cm), the mciroplasmas light emissions are always accompanied with microbubbles generation at various applied peak voltages (-3kV to -12kV). For a low conductivity (1990μS/cm), there were thresholds of applied peak voltage for different phenomenon of the microplasmas and the microbubbles. With the applied peak voltage in the range of 0kV to -4kV, neither the microbubble formation nor the detectable microplasma slight emission was observed by ICCD and PMT. With the applied peak voltage in the range of -4kV to -6kV, the visible microbubbles was able to be observed, but no microplasma light emission could be detected by both ICCD and PMT. With the applied voltage larger than -6kV in magnitude, both of the visible microbubbles and microplasma light emission can be observed. The thresholds of applied peak voltages are determined from observations.