Plasma

A novel system aiming to electrically supply various cold plasma generators is proposed. It operates as a programmable linear current source which is able to maintain a dc constant discharge current at various discharge voltages required to sustain the plasma jet. Its design is based on a specific electronic device called a switchable current regulator, which considerably simplifies the circuit topology. Experimental results carried out in real operating conditions confirm the practical purpose of the proposed solution.

The generation of atmospheric pressure nonequilibrium plasma using electrical discharges is an active area of research due to its significance in a wide spectrum of applications including medicine, combustion, and manufacturing. In our attempt to create a helium plasma jet in a pin-plane discharge with a constant current source, we observed self-pulsating behavior. We present the results of the electrical, optical, and spectroscopic measurements carried out to characterize the discharge. The duration of the discharge is a few tens of nanoseconds, and the repetition rate is in the few tens of kHz. The effect of the gap distance and gas flow is discussed. The effective capacitance formed by the space charge in the discharge region plays an important role in determining the pulsing frequency. The results of voltage swing, current pulse, and light emission are also discussed. Such self-pulsating discharges can be used to produce helium plasmas under ambient conditions in applications such as plasma medicine.

Filamentary mode, as a common phenomenon that appears in dielectric barrier discharge (DBD), is realized by rod-to-rod electrodes in N₂-O₂ mixtures at 80 mbar. The effects of the dielectric thickness on the characteristics of filamentary DBD are investigated through experiments and simulations. The discharges are driven by a positive unipolar nanosecond pulse voltage with 15.8 kV amplitude, 9 ns rise time (T_r^10–90%), and 14 ns pulse width. The characteristics of filamentary DBD are recorded with an intensified charge-coupled device and a Pearson current probe in the experiment, and a 2D axisymmetric fluid mode is established to analyze the discharge. Surface discharges occur on the anode and cathode dielectric after the breakdown, and the discharge is gradually extinguished as the applied voltage decreases. A thinner total dielectric thickness (D_a + D_c) leads to larger currents, stronger discharges, and wider discharge channels. These characteristics are consistent when the total dielectric thickness is the same but anode dielectric thickness and cathode dielectric thickness are different (D_a ≠ D_c ≠ 0). If the anode is a metal electrode (D_a = 0), the current will be substantially large, and two discharge modes are observed: stable mono-filament discharge mode and random multi-filament discharge mode. It is found in simulations that the dielectric thickness changes the electric field configuration. The electric field is stronger with the decrease in dielectric thickness and leads to a more intense ionization which is responsible for most of the observed effects.