Effect of pulse energy on the dynamic development of spark-plasma-jet driven by nanosecond high-voltage pulse

Abstract

We investigated the spatial-temporal dynamics characteristics of the spark-plasma-jet (SPJ) in the nitrogen of 0.1 MPa at different pulse energies by fast photography and optical emission spectrum. The spark plasma generated by spark discharge can be rapidly sprayed out of the micro-incentive cavity within several tens nanoseconds under the action of electric field, and the spraying delay time reduces gradually with increase of pulse energy. The outlet velocity of SPJ reaches up to 10 4 m s −1 . After that, the propulsion velocity decreases dramatically by 1 or 2 orders of magnitude at 2 μs. These two striking features were observed during the SPJ propulsion period. Firstly, there are two propulsion modes including 'plasma column' and 'plasma bullet' appearing in the development of SPJ successively. The conversion from plasma column to plasma bullet is slowed down with the increase of discharge current duration. Secondly, the inner form of SPJ exhibits the 'halo', 'corehalo' and 'tree' patterns respectively at the pulse energies of 1.6 J, 32 J and 160 J. Furthermore, the distribution morphology of SPJ obviously has flow field features. In order to accurately estimate the spatial-temporal distribution of electron parameters by optical emission spectroscopy diagnosis, the electron temperature was calculated by the Boltzmann plot method and continuum radiation, respectively, and the electron density was calculated by the Saha equation and Stark broadening respectively. The results show that the electron temperature and electron density of SPJ are 1.7 eV∼2.9 eV and 8.5×10 16 /cm 3 ∼1.0×10 18 /cm 3 respectively in different conditions. These results provide some fundamental knowledge about the dynamic development of SPJ.

Design and characteristics investigation of a miniature low-temperature plasma spark discharge device

“…The plasma propagation velocity drops sharply to 0.75 km s −1 in 4 μs, and then slowly decreases to zero in around 30 μs. The average velocity of the plasma is calculated to be 0.56 km s −1 for this spark discharge, similar to previous relevant reports on spark plasma jets [28,29].…”

“…N 2 (C-B) can be found in the region of 380-450 nm [34]. A second positive band of nitrogen molecules is detected at between 450 nm and 550 nm [35], and the first positive band is measured at between 620 nm and 700 nm [28,36]. The nitrogen atom was measured at 780 nm and the oxygen atom at 610 nm [36].…”

“…This is because increasing the applied voltage can improve the discharge energy and transferred charge, which are input into the spark reactor when the air gap is broken down. The increased energy and charge enable the plumes to propagate to a longer distance [28][29][30].…”

“…where C is around 0.33 F and U 2 is around 3 kV. Then E is estimated to be 1.48 J, which is large enough to generate a peak current with a magnitude of several hundred amperes [28,32].…”

“…The ICCD images mainly reveal the time evolution of the discharge particle optics and motion trajectory. In addition, the spark discharge rapidly heats and presses the gas, and the gas is exhausted through the small holes to form a gas jet stream at a velocity of up to 10 km s -1 [28]. With the ICCD images, the velocity v of spark plasma can be estimated by…”