Developmental Research in Nanosecond Spark Source for Visualizing High-Speed Phenomena

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A simple nanosecond spark source (Nanospark) has been constructed from several small ceramic capacitors, one thyratron and one coaxial cable. During operation, a 500-1400 pF capacitor in the spark head is pulse-charged in about 60 ns with automatic preionization from a high-voltage pulse generator switched by a thyratron. This charge is available for discharge when the gas breakdown starts. The preionization is useful to start the gas breakdown easily and to decrease the pulse-to-pulse time jitter. This Nanospark produces 12-30 ns (FWHM) light pulses with a time jitter of less than 60 ns when perated at 6-14 kV and in air of atmospheric pressure. The initiation of the spark gap is highly reliable and the radiation channel is very stable. The spark has adequately exposed customary ASA 100 film in various schlieren and shadowgraph systems and some shock wave visualizations have been obtained. In colour schlieren systems, however, high-sensitivity colour films of ASA 1600 were needed.Some … More features of the described spark source can be improved and enhanced by pressurizing the gap : in a slightly modified version of the source, the spark can be initiated in practically any gas of almost arbitrary pressure. The light intensity and the pulse width increase with the gas pressure. If the pulse width is of but minor consequence, the quantity of radiation can be increased tenfold with a Xe-filled chamber. The spectral study showed that the light intensity with Xe-gas increases somewhat toward the infrared region. In this way we obtained colour schlieren photographs with ASA 400 films.The described light sources, due to their novel preionization technique and their practical design, fulfill the requirements for being employed in optical short duration measurements, particularly in visualization of high speed phenomena. The light output is sufficient for high quality single-shot photography making these sources at least equivalent if not superior to comparable commercially available equipment. Less