In this paper, we described the fabrication and testing of a novel plasma-jet triggered gas switch (PJTGS) operated at extremely low working coefficients with excellent triggered jitters. While the structure of the PJTGS is similar to that of a traditional three-electrode field-distortion gas switch, to improve its triggered performance we used a conical micro-plasma-gun with a needle-to-plate spark gap embedded in the trigger electrode. Applying a nanosecond pulse to the trigger electrode caused a spark discharge in the micro-plasma-gun. The electric field drove the discharge plasma to spray into the spark gap of the gas switch, causing fast breakdown. We tested the PJTGS with charging voltages of ±25 kV and a trigger voltage of +80 kV (5 ns rise time and 80 ns full width at half maximum) in two working modes. The PJTGS operated in Mode II had a lower triggered jitter and could be operated over a wider range of working coefficients than in Mode I under the same conditions. At working coefficients higher than 70%, we obtained sub-ns triggered jitters (<0.89 ns) from the PJTGS, at working coefficients lower than 50%, we obtained triggered jitters of 1.6-3.5 ns without no-fires or pre-fires. Even at a working coefficient of 27.4%, the PJTGS could still be triggered reliably with a delay time of 96.1 ns and a triggered jitter of 3.5 ns, respectively.

No abstract

The plasma-jet triggered gas switch (PJTGS) could operate at a low working coefficient with a low jitter. We observed and analyzed the discharge process of the PJTGS at the lowest working coefficient of 47% with the trigger voltage of 40 kV and the pulse energy of 2 J to evaluate the effect of the plasma jet. The temporal and spatial evolution and the optical emission spectrum of the plasma jet were captured. And the spraying delay time and outlet velocity under different gas pressures were investigated. In addition, the particle in cell with Monte Carlo collision was employed to obtain the particle distribution of the plasma jet varying with time. The results show that, the plasma jet generated by spark discharge is sprayed into a spark gap within tens of nanoseconds, and its outlet velocity could reach 10 4 m s −1 . The plasma jet plays a non-penetrating inducing role in the triggered discharge process of the PJTGS. On the one hand, the plasma jet provides the initial electrons needed by the discharge; on the other hand, a large number of electrons focusing on the head of the plasma jet distort the electric field between the head of the plasma jet and the opposite electrode. Therefore, a fast discharge originated from the plasma jet is induced and quickly bridges two electrodes.

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.

No abstract