If I understand you correctly you wanna submerge a DPF in heavy water (deuterium plus oxygen). Then with an electric discharge you’re creating a bubble big enough to to cover the complete DPF, including the base, the insulator, the electrodes. And this perfectly, otherwise the sheath will go astray. Within that bubble it’s 10GPa, or is it just the initial pressure (probably much more so, I suppose). Ok, that bubble expands from tiny (10GPa) up to the size of the DPF, then it’s maybe the required 1kPa (10mbar) for the sheath to form. Remember, you need a vacuum for the DPF to work. Nothing gained compared to a gaseous deuterium/oxygen mixture, and oxygen is a bad idea for short lived fusion anyway.
