Shadowgraphic study of plasma dynamics in a miniature plasma focus device under repetitive operation

Abstract

Summary form only given. The optical investigation of the plasma dynamics in breakdown, axial and radial phases of fast miniature plasma focus (FMPF-3) device under repetitive opeartion is being performed by means of laser shadowgraphy. Uniform parallel light beams are provided by using a monochrome (532 nm) Nd:YAG short pulsed laser (120 ps). A Phantom V211 high speed camera with a maximum resolution of 1280 × 800 pixels and minimum exposure time of 2 μs is used to capture the images. All sequential signals with adjustable timing are provided by a programmable STM32f4 microcontroller board which allows the user to preset all required timing for each of the individual devices. A series of shots are performed, at different repetition rates, with automatic time increasing with reference to a selected reference time instant on discharge current. After each set of experiments, the sequence of the images from the laser shadowgraphy is correlated with the current derivative signal. The results show the different shape, size and density of the plasma sheath and final pinch column for pure hydrogen/deuterium and admixture gas operation. They also illustrate the MHD instability formation in different gas pressure and admixture ratios.