Negative Pressure Measurements at Cavitation Induced by an X-ray laser in Water Microdroplets

The understanding of cavitation in stretched water is incomplete, in part due to the difficulty of achieving homogenous nucleation at room temperature. Although the mineral inclusion technique reached homogeneous cavitation pressures as low as -140 MPa, most other studies observed cavitation before reaching -30 MPa. Recently, we achieved pressures below -30 MPa by ablating droplets with X-ray laser pulses, which induces spallation. We estimated negative pressures below -100 MPa when spall cavities appeared, but this was a low-accuracy estimate based on analytical approximations, and cannot confirm homogeneous nucleation. To improve the accuracy, we collected better experimental data which we model using CFD simulations. The parameters of the CFD simulations are first optimized to match the drop surface motion due to the reflection of ablation shock waves. The CFD simulations then provide the evolution of negative pressure over time, and the peak negative pressure is extracted when the spall cavity is formed. The combined experimental and CFD approach confirmed the pressure range obtained with analytical approximations, and we will report refined measurements of the negative pressures reached before cavitation.