  In this study we have studied the initial stage of the nanosecond-pulsed
discharge development in liquid phase. Modeling predicts that in the case of
fast rising strong nonhomogeneous electric fields in the vicinity of high
voltage pin electrode a region saturated with nanoscale non-uniformities may be
developed. This phenomenon is attributed to the electrostriction mechanisms and
may be used to explain development of breakdown in liquid phase. In this work,
schlieren method was used in order to demonstrate formation of negative
pressure region in liquids with different dielectric permittivity constants:
water, ethanol and ethanol-water mixture. It is shown that this density
perturbation, formed at the raising edge of the high voltage pulse, is followed
by a generation of a shock wave propagating with the speed of sound away from
the electrode, with negative pressure behind it.
