Session PR1: Atmospheric Plasmas I

Tailoring the electron dynamics and chemical kinetics in radio-frequency driven atmospheric pressure plasmas

Radio-frequency atmospheric pressure plasmas are versatile and efficient sources for reactive species at ambient room temperature. The non-equilibrium chemical kinetics is initiated and determined by the electron dynamics. Due to the strongly collisional environment and associated short electron energy relaxation times the electron dynamics can be tailored using multi-frequency power coupling techniques, enabling separate control of key parameters like electron density and electron mean energy. Details of the chemical kinetics depend on the feedgas composition and desired application. Measurements and predictive simulations of key reactive species are equally challenging due to the strongly collisional environment and their multi-scale nature in space and time. The most promising approach is the exploitation of complementary advantages in direct measurements combined with specifically designed numerical simulations. The employed diagnostic techniques include picosecond laser spectroscopy, synchrotron VUV spectroscopy, IR absorption spectroscopy and nanosecond optical imaging spectroscopy. The presentation will focus on examples of He-O$_2$-N$_2$ mixtures for bio-medical applications and He/Ar-CO$_2$ mixtures for CO$_2$ conversion into value-added chemicals.   

Nonlocal effects in electron heating in atmospheric pressure capacitively coupled discharges

The present work discusses different aspects contributing to the excitation (ionization) pattern formation in highly collisional capacitively coupled discharges operated under atmospheric pressure in the $\Omega$ mode by using analytical arguments and results of numerical simulations. Whereas it is common to explain an observed excitation pattern by using the corresponding power absorption profile, it is argued that the two are essentially different, the former possessing an exponential dependence on the electric field in contrast to the latter. Therefore, the peaks in the profiles of the excitation rate and the absorbed power can take place at different spatial locations. A novel effect, previously unreported for the high pressure discharges, is observed, where spatial location of the peak in the excitation profile is shifted by a distance approximately equal to the energy relaxation length from the peaks in the absorbed power and the electric field profiles. This intrinsically nonlocal and kinetic (the energy relaxation length being much larger for the high energy compared to the low energy electrons) effect is particularly pronounced when the electric field is strongly nonuniform with the scale comparable to the energy relaxation length.   

Influence of quenching gas injection on the temperature field in pulse-modulated induction thermal plasma for large scale nanopowder synthesis

We have so far developed a unique and original method for a large-scale nanopowder synthesis method using pulse-modulated induction thermal plasmas with time-controlled feedstock feeding (PMITP-TCFF). The PMITP is sustained by the coil current modulated into a rectangular waveform. Such the current modulation produces an extremely high-temperature thermal plasma in on-time, and in off-time relatively low-temperature thermal plasma. In PMITP-TCFF method, feedstock powder is intermittently injected to the PMITP synchronously during only on-time for its efficient and complete evaporation. That evaporated materials are rapidly cooled down to promote nucleation of nanoparticles during off-time. This report deals with a numerical approach on influence of quenching gas injection on the temperature field in the PMITP. The thermofluid model for the PMITP was developed on the assumption of local thermodynamic equilibrium (LTE). This model accounted for the pulse-modulation of the coil current and the quenching gas injection. It was found that the quenching gas injection works to increase the PMITP temperature inside the plasma torch during on-time, and then to decrease it effectively in the reaction chamber.   

Modeling of Thermal Arcs in Molded Case Circuit Breakers in Air

A general-purpose thermal plasma simulation tool (VizArc) was utilized to model a circuit breaker in atmospheric pressure air. The molded case circuit breaker (MCCB) circuit breaker works by separating two metal contacts when the breaking current is exceeded generating an arc. The self-consistent Lorentz force generated by the current pushes the arc into an array of splitter plates which quench the arc and break the circuit. The arc channel is modeled by coupling the electromagnetic equations with flow governing equations to model a multi-species, single-temperature quasi neutral arc plasma. Conjugate heat transfer to the metal splitter plates and vapor ablation into the gas are included in the model. The opening action of the moving contact armature is simulated dynamically in the simulation. The set of all governing equations and their implementation in the model will be discussed, and then the simulations of the MCCB circuit breaker using the model will be presented.   

Preliminary Study on Generating Condition of Laser Sustained Plasma using 1 kW CW Diode Laser

In the laser sustained plasma of conventional laser driven plasma wind tunnel, CO2 laser have been used. However, the efficiency of is about 10 {\%}. Recently, the development of diode laser is remarkable and the energy efficiency of it reaches nearly 80 {\%} in laboratory stage. Therefore, in our research group, the generation of laser sustained plasma using diode laser is being tried. In this study, the generation threshold of it was numerically calculated. Assuming that focused laser diameter is 200 um, in the condition of the pressure of 0.1-1 MPa, it was deduced that the threshold of laser power is about 500 W.