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The microwave electrothermal thruster (MET) utilizes wave-exited microdischarges to heat gas flows, enhancing the specific impulse of the thruster. Our computational study investigates a 17.5 GHz helium-propellant MET, employing a two-dimensional, axisymmetric fluid model of plasma coupled with electromagnetic wave and gas flows. The discharges operate in the glow regime, remaining weakly ionized, and in thermal non-equilibrium. The plasma densities reach approximately 10 20 m − 3 , and the gas temperature is around 2000 K. Even a slight off-resonant frequency operation results in a significantly lower plasma density and gas temperature. Gas heating, primarily driven by electromagnetic Joule heating, plays a critical role in influencing the overall discharge behavior. The measured peak thrust and specific impulse are 8.24 mN and 292 s, respectively, at a mass flow rate of 3.2 mg/s with 30 W of power. Compared to a cold gas thruster, there is a significant increase in the specific impulse by a factor of approximately 1.7. The enhanced performance trades off with propulsive efficiency, which decreases by a factor of 1.5 from the peak 65% at 10 W. This is due to higher energy losses to cavity walls from heat conduction with increased power. These findings underscore the critical balance between the input power and mass flow rate to improve the MET performance, highlighting the importance of power management to maximize thrust and efficiency. Furthermore, the predicted thrust and specific impulse agree well with experimental values for nominally similar MET thruster studies in the literature. [ABSTRACT FROM AUTHOR]

In recent years, interest in synthetic C4F7N as a gas insulator has been growing due to its unique insulation properties and low global warming potential. In spite of this, very few studies are devoted to the analysis of the electric breakdown of C4F7N and its mixtures with other dilutants such as CO2 and N2. In the present paper, we use a two-dimensional fluid model to analyze the electrical breakdown of the atmospheric pressure C4F7N/N2 mixture. We establish the influence of the C4F7N fraction in the mixture and the cathode voltage rise rate on the breakdown voltage. We find that the ratio between the electron attachment frequency and the voltage rise rate defines the streamer parameters. Namely, if the time scale of electron attachment to C4F7N is much faster than the voltage rise rate, the plasma electronegativity of the streamer body and of its head is extremely high, and it is difficult to define exactly the streamer head location. In the opposite case of the fast rise rates, the conventional streamers with sharp heads were obtained. [ABSTRACT FROM AUTHOR]

The main aim of the present paper is to clarify the influence of the SF6 fraction in the SF6/N2 mixture on the breakdown voltage. For this, the two-dimensional axisymmetric fluid model coupled with the comprehensive mechanism of plasma chemical reactions is used. In addition, the influence of various parameters such as the voltage rise time and the SF6 fraction in the mixture is analyzed. It is observed that depending on the voltage rise time an admixture of only 1% of SF6 to N2 results in an increase in the breakdown voltage by 7%–43%. The sensitivity of breakdown voltage decreases with decreasing voltage rise time and is caused by the electron attachment time scale becoming comparable to the breakdown time. The results of simulations confirm that the increase in the SF6 fraction in the mixture leads to an increase in the breakdown voltage. This is explained by the influence of the SF6 fraction on the electron attachment rate coefficients rather than on the ionization reactions. [ABSTRACT FROM AUTHOR]

The influence of electron field emission on the sub-normal mode of a magnetized direct current high-pressure helium discharge is analyzed using the two-dimensional axisymmetric fluid model. It is observed that in spite of accounting for a more intense electron emission mechanism, discharge still operates in the sub-normal mode. However, the field emission driven discharge is characterized by a smaller discharge voltage and a larger discharge current. For large values of the electric field enhancement factor, the discharge voltage can be as low as ∼40 V, and the discharge current is a few amperes. It is also seen that for large values of the field enhancement factor and small values of the ballast resistor, rather dense plasma (density ∼ 1017 m−3) can be generated on the nanosecond time scale. [ABSTRACT FROM AUTHOR]

Plasma-produced NxHy radicals facilitate the removal of native oxide layers in a semiconductor wafer surface. A remote microwave excited plasma with a NH3–N2 feed gas is used commonly to produce the active radicals. We perform a three-dimensional modeling of a microwave excited plasma operating in a surfatron mode. The device consists of a rectangular waveguide intersecting a quartz tube through which the feed gas flows. We discuss the propagation of a polarized 2.45 GHz microwave from the waveguide into the quartz tube where power is deposited into the plasma. The plasma–wave interaction is found to be highly three dimensional, with a propagating surface mode of the wave established along the dielectric tube plasma interface. Significant heating occurs on the side of the tube that directly faces the incident wave. As the flow carries the plasma-produced species down the tube, species radial profiles become increasingly diffusion controlled and axisymmetric. The dominant radicals that exit the tube are H2 and NH2, with nearly complete conversion of the feed gases to product species. The gas temperature rises above this inlet feed gas temperature and increases with increasing wave power. However, the gas temperature increase is not consequential to the overall radical yield from the plasma. The parametric study with changing pressure and input power illustrates the role of specific chemical reactions in the overall remote plasma process. [ABSTRACT FROM AUTHOR]

Iodine is being studied as an alternative propellant for electric propulsion application as it has numerous advantages over commonly used xenon gas. In spite of numerous experimental studies for the conditions typical for electric propulsion, there are very few computational modeling studies of iodine plasmas: all with reduced geometric representations in zero or one dimension. In the present paper, we use self-consistent two-dimensional fluid model coupled with Maxwell's equations to analyze the inductively coupled plasma generated in low-pressure iodine. We compare the plasma parameters for two values of the background pressure: 1.0 and 2.5 Pa. We find that ∼99% of the molecular iodine is converted into atomic iodine. As a result, plasma consists of electrons, ions I+, and a significant number of negative ions I−. The density of molecular ions I2+ is much smaller than the density of I+. We analyze the transport of these species for two pressures and show that there are different regimes of plasma diffusion realized for the conditions of our studies. We also study how the discharge power influences the plasma parameters such as the electron and ion densities and the electron temperature. [ABSTRACT FROM AUTHOR]

A high-pressure direct current magnetron discharge is analyzed using a self-consistent two-dimensional fluid model. This discharge has potential interest in plasma switching applications due to its ability to generate rather dense (plasma density of ∼1019 m−3) stable nonequilibrium plasmas at pressures of ∼13.3 Pa (100 mTorr). This discharge has several advantages over nanosecond pulsed high pressure discharges used in conventional plasma switchers since it operates at much lower voltages and lower gas pressures, with the advantage of much longer cathode lifetime. In the present paper, we analyze the operating modes of this magnetron discharge for conditions close to that of Sommerer et al. [J. Phys. D: Appl. Phys. 52, 435202 (2019)]. We observe the subnormal and normal modes of the magnetron operation whose physics differs from that typical for unmagnetized plasmas. [ABSTRACT FROM AUTHOR]

We present a computational study that demonstrates the concept of a microwave excited plasma flow sensor. The geometric configuration consists of an array of circularly arranged "receiver" (ground) electrodes that surround a central "transmitter" (excited) electrode that is flush mounted on a surface exposed to incident flow. Microwave excitation is used to strike a low-temperature plasma between the transmitter electrode and the receiver electrode. Depending on the flow direction, a more intense plasma kernel is formed between the transmitter electrode and the downstream electrode for sufficiently strong excitation conditions. The differential current between the receiver electrodes is used to establish the flow direction and magnitude. The computational model establishes the effectiveness of the concept as a flow sensor. Parametric studies involving excitation voltages, flow velocities, scale lengths, electrode shape, and excitation frequency are performed. It is observed that the sensitivity of the device to the imposed flow is considerably improved with increasing excitation frequency in the microwave regime. [ABSTRACT FROM AUTHOR]

Direct current micro-plasmas in the non-homogeneous electric field are analyzed over a wide pressure range using the self-consistent two-dimensional axisymmetric fluid model. We observe that the breakdown voltage is not the unique function of Pd, where P is the gas pressure and d is the interelectrode spacing, but also depends on the aspect ratio d/r, where r is the anode radius. This result agrees with the data reported in the literature. For fixed d, we find two modes of ionization wave propagation on the right branch of the breakdown curve: an axial streamer mode that is obtained at low pressures and a hollow streamer mode obtained at high pressures. By varying the ballast resistance connected to the anode, we analyze the steady-state parameters of the micro-discharge for the cathode–anode gap of 200 μm. We obtain normal and sub-normal glow modes of the micro-discharge operation. The instability of the latter mode is analyzed. [ABSTRACT FROM AUTHOR]

We demonstrate through numerical experiments and analytical calculations that extreme subwavelength gaps between two corrugated surfaces support high effective refractive index guided modes. The corrugated gap mode is of low loss because it does not rely on plasmonic currents induced inside a metal. This enables guided modes with a much higher effective refractive index than is possible in natural plasmonic materials. These high-index guided modes are incorporated as periodic slots in an opaque screen, which is then shown to support broadband highly transmitting modes at a certain oblique incidence angle in addition to the usual Fabry–Pérot resonances. This anomalously high transmission is the extension of the plasmonic Brewster angle to arbitrarily low frequency, controlled by the geometry of the corrugated slots. We demonstrate the preservation of the shape of a broadband low-frequency pulse transmitted through the slotted screen, opening up the possibility to use the structure for broadband energy squeezing applications in the GHz to THz regime. [ABSTRACT FROM AUTHOR]

The objective of this paper is the validation of a surface reaction mechanism for silicon etching in low-pressure chlorine plasmas. We employ a quasi-one-dimensional fluid model to model the experimental conditions of Khater and Overzet [Plasma Sources Sci. Technol. 13, 466 (2004)]. This model couples self-consistently the plasma fluid equations with the surface reaction mechanism derived from the available literature. Based on the comparison between the experiments and modeling results, the best set of etch yield parameters is proposed for the conditions typical for industrial plasma processing. The influence of these etch yield parameters on the gas-phase plasma is also discussed. [ABSTRACT FROM AUTHOR]

A computational model for the interaction of a high-pressure microplasma with an electromagnetic wave is presented. A one-dimensional particle-in-cell Monte Carlo collision model is used to investigate the plasma non-ideality effects in a second-stage laser-heated xenon plasma with a comprehensive chemistry mechanism, including excited species. A xenon microplasma at a temperature of 300 K and pressure of 10 bar becomes non-ideal after the laser heating stage with lower ionization and electronic excitation barriers, which makes the presence of excited species important to the plasma generation process. For these conditions, two-step ionization via excited species becomes a major contributor to plasma ionization. We find that full ionization of the plasma is obtained in ∼2 ps when excited species are included in the chemistry model, as opposed to ∼2.5 ps for a chemistry mechanism that does not consider their effect. With excited species, the ionization mode transitions from direct ionization via electron-neutral collisions to direct and stepwise ionization as the plasma generation progresses. [ABSTRACT FROM AUTHOR]

Using a self-consistent plasma model coupled with Maxwell's equations, the limitations of independent control of ion fluxes and their energy distribution functions extracted from the high-density inductively coupled chlorine plasma are studied. Two extreme cases of discharge power are considered: 100 W and 1 kW. We find that in the low-power case, plasma is mainly generated by electromagnetic waves while the radio-frequency biased electrode primarily enables plasma ion extraction. Therefore, the ion fluxes and distribution functions are controlled independently. For the high-power case of 1 kW, the bias electrode significantly contributes to plasma generation but has only a small effect on sheath voltage. As a consequence, independent control of ion fluxes and distribution functions becomes impossible. Namely, the increase in the power driving the radio-frequency electrode leads to the increase in the ion fluxes but has little effect on their energy and angular distributions. [ABSTRACT FROM AUTHOR]