Temporal emission behavior of pulsed discharge in water

To move the high energy pulsed power systems from the laboratory to practice requires the development of compact lightweight drivers. To reduce the size and weight of high voltage components, increase in the energy density in dielectrics at high electric stress is required. Therefore, an in-depth understanding of the hold-off voltage and breakdown properties of liquid dielectrics can lead to the optimization of energy storage. When breakdown is initiated in liquid dielectrics, vapor bubbles are generated, which first expand and later collapse. The total time of expansion and collapse of these bubbles determines the repetition rate at which high voltage switches can be operated. In this paper, a Blumlein pulse forming network (PFN) and sphere-plane electrode configuration is used for studying a pulsed discharge in water. The diameter of the spherical electrode is 1.7 mm and the gap distance between the electrodes is several hundred micrometers. The temporal development of the optical emission in the UV and visible after breakdown was measured by means of an imaging spectrograph. The radiation intensity reaches its maximum 5 ns after breakdown. It remains at this level for about 100 ns, and then the light intensity decreases to 30% of its peak value on a 10 ns time scale. The current was found to be 800 A during the pulse. The radiation spectrum of the plasma in the bubble during the 100 ns after breakdown was also measured. No line radiation was observed. The measured spectrum was found to follow a blackbody radiation law. Therefore by comparing the measured spectrum with that of calculated blackbody radiation at different temperatures, the plasma temperature was determined. It was found to be in the 1-2 eV range.