The continual and increasing use of fossil fuels throughout the world has advanced concerns of atmospheric carbon dioxide (CO 2 ) concentrations, causing a swell of scientific interest to ease the predicted effects of global warming. This work experimentally investigates the conversion of CO 2 to carbon monoxide (CO) and oxygen in an atmospheric pressure microwave plasma/catalyst system. Diagnostics such as mass spectrometry and optical emission spectroscopy are used to identify the gas species present after plasma treatment and to measure plasma temperatures. The CO 2 gas is first treated with plasma alone, and is then treated with a combination of plasma and rhodium (Rh) catalyst material. While the plasma system alone is able to achieve a 20% energy efficiency, the Rh catalyst actually causes a drop in efficiency due to reverse reactions occurring on the surface. The plasma temperature measurements indicate thermal equilibrium between T r and T v around 6000-7000 K.

One possible solution to mitigating the effects of high atmospheric concentrations of carbon dioxide (CO 2 ) is the use of a plasma source to break apart the molecule into carbon monoxide (CO) and oxygen. This work experimentally investigates the efficiency of dissociation of CO 2 in a 1-kW radio-frequency (rf) plasma source operating at 13.56-MHz in a low-pressure discharge. Mass spectrometry diagnostics are used to determine the species present in the discharge, and these measurements are used to calculate the energy efficiency and conversion efficiency of CO 2 dissociation in the rf plasma source. Experimental results have found that the conversion efficiency of CO 2 to CO can reach values near 90%, however energy efficiency reaches a maximum of 3%. A theoretical energy cost analysis is also given as a method to evaluate the effectiveness of any plasma system designed for CO 2 emissions reduction.

High-speed imaging of a Hall thruster plume reveals near-omnipresent rotating regions of elevated light emission, dubbed rotating spokes, in the annular thruster discharge channel. Azimuthal oscillations have long been suggested to induce crossfield electron transport in Hall thrusters, but conclusive experimental identification of such oscillations with probes is often challenging. However, simple processing of high-speed images taken at a few tens of thousands of frames per second clearly reveals long-wavelength rotating spokes at very low frequencies, corresponding to velocities of only a few hundred meters per second.Index Terms-Image sequence analysis, plasma devices, plasma diagnostics, plasma waves. H ALL thrusters are space propulsion devices that use electromagnets to create a strong radial magnetic field across a generally annular discharge channel, suppressing axial electron mobility toward the anode at the base of the channel and thus sustaining strong axial electric fields for ion acceleration without acceleration grids. While Hall thrusters have a flight heritage of nearly 40 years, the high cost of vacuum chamber testing to optimize performance and validate lifetimes for ever higher power thruster designs increasingly motivates development of predictive Hall thruster models.The primary hurdle to a predictive Hall thruster plasma model is our poor understanding of the mechanisms of electron transport across the strong magnetic fields in the thruster plasma. One theory often suggested to drive cross-field transport is the formation of axial E × B drift currents due to the applied radial magnetic field and induced azimuthal electric field components in plasma instabilities. Such instabilities have been measured at low frequencies using in situ plasma probe arrays [1] and at high frequencies with collective light scattering laser techniques, [2] but both methods are inherently local, making it difficult to accurately estimate global levels of electron transport by this mechanism.High-speed imaging can nonintrusively capture a wealth of qualitative information about the entire thruster plasma at a glance, for example, fluctuations in total image brightness summed over all image pixels correlate strongly with discharge current oscillation spectra, a common diagnostic assessment Manuscript of thruster operating stability. The combination of high-speed imaging with local plasma probes has the potential to enable quantitative global thruster calculations as well, by scaling visible wave structures on camera to match measured plasma properties such as potential and density. Plasma density fluctuations have already been observed in rotating spokes in a small cylindrical Hall thruster using synchronous high-speed imaging with in situ Langmuir probes, [3] at frequencies similar to those measured with plasma probes alone in [1].Here, we present images of a nominal 6-kW class laboratory Hall thruster showing the clear presence of coherent rotating spoke structures, with frequencies in the low single kilohertz and...

The Plasmadynamics and Electric Propulsion Laboratory High-speed Axial Reciprocating Probe system is used in conjunction with a floating emissive probe to measure plasma potential in the discharge chamber of the P5 Hall thruster. Plasma potential measurements are made at a constant voltage, 300 V, at two different discharge current conditions: 5.4 and 10 A. The plasma potential contours for the 5.4 A case indicate that the acceleration region begins several millimeters upstream of the exit plane, extends several centimeters downstream, and is uniform across the width of the discharge chamber. The 10 A case is similar to the 5.4 A case with the exception that the acceleration region is shifted downstream on centerline. Axial electric field profiles, computed from the measured potential, show a double peak structure in the 5.4 A case, indicating a zone of ion deceleration. Perturbations to the discharge current are shown to correspond spatially with the location of the peak electric field indicating that thruster perturbations may result from a disturbance to the Hall current, as opposed to ablation of probe material. This conclusion is supported by the lack of any observable material ablation.