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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Interactions of a Microdischarge with a Premixed Flame (Final Technical Report)

In this project we introduced an experimental platform that facilitates the study of the two-way interaction of plasma and flame, and the exploration of the impact of the spatial location of the discharge on its kinetics, in a controlled environment. The experimental platform is a mesoscale CH4/air premixed flame burner that also acts as a dielectric barrier discharge (DBD) operated by nanosecond pulsed voltage. A unique feature of this setup is that the DBD utilizes transparent electrodes, made of Indium Tin Oxide (ITO), to unlock optical access along the line-of-sight parallel to the dominant electric field. This platform is suitable to study both the forward problem (impact of plasma-on-flame), which manifests itself as a modified flame speed as well as flame wrinkling; and the backward problem (impact of flame-on-plasma), which includes plasma regime transitions, between microdischarges and uniform modes, driven by the flame passage. Prior work at MIT has focused on electrical measurements and direct imaging studies of the plasma-flame interaction through the ITO electrode. This project, which was awarded experimental runtime at the Low-temperature Plasma Research Facility (PRF) at Sandia National Laboratories, quantifies the flame-plasma interaction through temporally resolved measurement of key radicals (oxygen atom, O) produced by the nanosecond repetitively pused discharge (NRPD) in an individual microdischarge, using two-photon absorption laser-induced fluorescence (TALIF).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Anomalous Retrograde Drifts in Obstructed Magnetron Microdischarges: a Consequence of a Field Reversal in the Anode Sheath?

The goal of this project was to carry out experiments at the Plasma Collaborative Research Facility (Princeton Plasma Physics Laboratory) aimed at confirming or refuting the hypothesis that an electric field reversal occurs in the near-anode region of a strongly obstructed planar magnetron microdischarges. Magnetron discharges are magnetized plasmas with E x B field topologies, and variants of such discharges are widely used in materials processing. The topologies are also similar to that of Hall thrusters used in space propulsion. Understanding the structure of these discharges will aid in developing reliable simulations that are intended to facilitate the further development of such technologies, as the field reversals, presumed to be due to strong axial-driven electron transport, provides further insight into transport properties. The possible existence of such a field reversal is hinted at because of the retrograde-propagating (i.e., negative E x B) spokes or gradient-driven drift instabilities seen in the high speed videos and segmented anode probing of the plasma. The presence of this field reversal should be reflected in the ion dynamics, particularly, in an ion drift towards the anode. The proposed experiments to be conducted at the PCRF are to characterize this anode-directed ion drift using state-of-the-art laser-induced fluorescence velocimetry. In particular, we seek to see if the near-anode ion velocity reverses direction when the external circuit is varied to alter the electron current demand imposed at the anode. Such an ion velocity reversal would confirm the mechanism, which is that the highly obstructed (small gapped) discharge produces strong axial gradients in plasma density, driving more electrons towards the anode then that demanded by the external circuit.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Transition from retrograde to prograde drift instabilities in a magnetron microdischarge

Rotating plasma structures, or “spokes,” in magnetized discharges characterized by perpendicular electric and magnetic fields have been seen in a growing number of studies and are believed to be the result of gradient-driven drift instabilities. Under certain conditions, we have shown the spoke’s rotation to be opposite to the E B direction, i.e., retrograde in its expected direction. Recently, we have linked such counter-intuitive rotation to a local inversion of the electric field. Here, we give further experimental evidence for this inversion and attempt to provide an explanation for a relatively distinct transition seen between retrograde and positive (prograde) drift. In the experiments, a partially magnetized plasma forms inside a magnetron device of mm radius operated with argon. Discharge current–voltage measurements are acquired for a range of argon fill pressure and inter-electrode spacing. We find two branches of operation—a low current branch of negative resistance, coinciding with the retrograde spoke rotation, and a higher current branch of positive resistance, coincident with prograde spoke rotation. We postulate that at low discharge currents, high magnetic field confinement leads to a large density gradient, causing more electron transport to the anode than that demanded by the external circuit. At higher currents, anomalous axial electron transport (across the magnetic field lines) becomes dominant, eliminating the conditions for field inversion. Here, the current thresholds for the field inversion are found to be sensitive to the argon pressure and inter-electrode spacing.

42 ENGINEERING↗
DOE OSTI2021

Transition characteristics and electron kinetics in microhollow cathode discharges

We demonstrate the transition characteristics and electron kinetics of microdischarges in a microgap with a cathode having microstructures using two-dimensional particle-in-cell/Monte Carlo collision (2d3v) simulations. It is found that the microdischarge is inside the hollow cavity at lower pressures, forming microhollow cathode discharges (MHCDs), while the dominant discharge moves outside the cavity at higher pressures, locating above the cathode rectangular protrusion tip. The spatial distributions of the microdischarge parameters (e.g., electric potential and electron density) are presented by capturing the transition characteristics. The electron kinetics of the microdischarges are examined based on the moment analysis of the electron Boltzmann equation. The collisional and non-collisional components of the electron power absorption are decomposed, which were seldomly investigated for microdischarges previously. The results provide fundamental insights into MHCD formation with a structured electrode at varying pressure conditions, which could be beneficial for the design and fabrication of microplasma devices in practical applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Self-Organization and Nitrogen Incorporation in Diamond-Like Carbon Microstructures Synthesized by Nonthermal Plasma

Nonthermal plasma activation of light alkanes is an encouraging decarbonization strategy to produce chemicals or fuels from abundant and/or flared carbon sources. However, prolific carbon growth on both the catalyst and electrode has limited its practicality, requiring additional knowledge of the carbon structure and growth mechanism before breakthroughs are realized. Furthermore, visual evidence is provided for nonuniform diamond-like carbon (DLC) microstructures that materialize in a coaxial dielectric barrier discharge (DBD) reactor flowing ethane and He at 278 K. Through a connection to known behaviors of DBD microdischarge patterns, the microstructure spacing was controlled by altering the applied voltage (ΔV) of the plasma or the burning voltage (U b ). Additionally, carbon valorization through nitrogen incorporation from N 2 was explored as an orthogonal solution to carbon mitigation, with N/C values >0.25 achieved and both sp 2 and sp 3 C–N bonding observed in the microstructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Direct current microplasma formation around microstructure arrays

We demonstrate the formation and transition behaviors of a microplasma around microstructure arrays at different gas pressures via two-dimensional particle-in-cell/Monte Carlo collision simulations. It is found that the microdischarge occurs outside the cathode microcavities at the lowest pressure and starts penetrating the microcavities with a curved sheath edge as the pressure increases. At higher pressure, coupled periodic microhollow cathode discharges (MHCDs) are formed inside the microcavities. Further increasing the gas pressure results in the disappearance of the MHCDs, and the dominant discharge shifts outside of the microcavity, locating above the protrusion tips. The effect of the space charge shielding on the discharge and the conditions for MHCD formation are discussed. The macroscopic discharge parameter scalings with the gas pressure and the electron kinetics are also examined. The results are helpful for deeply understanding the microplasma formation with nonplanar electrodes, which inform the scaling, design, and optimization of microplasma array devices across a wide range of pressure regimes in practical applications.

42 ENGINEERING↗
DOE OSTI2020

Experimental Investigation of Nanosecond and Subnanosecond Pulsed DBD in Atmospheric Air: Fast Imaging and Spectroscopy

Dielectric barrier discharge (DBD), as an easy and simple way of generation of non-thermal plasma, has found a number of applications in variuos fields. However, development of a homogeneous, or uniform, DBD that would operate at atmospheric pressure conditions in atmospheric air, would open a number of new applications in various fields from thin film coatings to plasma medicine. Unfortunately, at atmospheric pressure, a uniform DBD can be easily transformed into a filamentary dielectric DBD; therefore some serious issues arise, such as gas heating due to strong discharges in the random microdischarge channel and non-uniform energy distribution, which adversely affect applications. These issues traditionally are solved by the use of an appropriate working gas composition, an alternating current driving frequency, lowering of gas pressure, etc. The transitions between discharge modes in the same experimental conditions have been thoroughly investigated in nitrogen, rare gases and their mixtures with air and other gases. In many cases (for example, in plasma medicine), these methods, especially those related to gas composition and pressure, may not be applied in a convenient manner. Recent advances in pulsed power technology permitted application of much faster voltage rise times (including the subnanosecond range) and short (few nanoseconds) pulses, and revealed that uniform DBD can, in fact, be generated in atmospheric air. Such discharges are in the great interest for many applications, however to date there still little understanding of the mechanisms of their operation and characteristics. Currently, there is no adequate model of the uniform dielectric barrier discharge development in atmospheric air. Although extensive studies have been performed on understanding of the nature of the pulsed DBD uniformity, until now there is still little understanding of the mechanism of the DBD transition from the filamentary mode to uniform mode. One of the reasons for this is that development of streamers, and later – filaments, occurs on the sub-nanosecond and nanosecond time scales, and therefore requires imaging and other diagnostic techniques with corresponding speed of registration. Recently developed technologies allow such studies. Here we demonstrate that DBD uniformity strongly depends on applied electric field in the discharge gap. More specifically, the discharge uniformity may be achieved in the case when two conditions are satisfied: (1) stong overvoltage in the discharge gap (provided by fast rise times), when anode-directed streamers are formed, and (2) short pulse duration that prevents discharge overheating due to rising conductivity (current) which leads to formation of filaments. We show that by controlling the applied (global) electric field in ns-pulsed DBD, it is possible to control the uniformity of the discharge. In addition, this offers better control of the discharge chemistry due to local changes of electric fields and therefore electron energy distribution function.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1985

Fracto-emission from the peeling of pressure sensitive adhesives

The electron emission, positive ion emission, photon emission, and long wavelength electromagnetic radiation accompanying the peeling of pressure sensitive adhesives in vacuum are examined. These results are interpreted in terms of a previously presented model involving fracture-induced microdischarges which excite the fracture surfaces by particle bombardment.

Dickinson, J. T.↗
NASA NTRS1985

Photon and radiowave emission from peeling pressure sensitive adhesives in air

During separation of an adhesive from a polymer substrate in air, intense bursts of photons ('phE', for photon emission) and long wavelength electromagnetic radiation ('RE', for radiowave emission), similar to those reported earlier by Deryagin, et al. (1978) have been observed. In this paper, careful measurements of the phE time distributions, as well as time correlations between bursts of phE and RE, are reported. These results support the view that patches of electrical charge produced by charge separation between dissimilar materials lead to microdischarges in and near the crack tip. The role of these discharges in producing sustained phE after the discharge has been extinguished is also discussed.

Donaldson, E. E.↗
NASA NTRS1987

Spacecraft dielectric surface charging property determination

The charging properties of 127 micron thick polyimide, (a commonly used spacecraft dielectric material) was measured under conditions of irradiation by a low-current-density electron beam with energy between 2 and 14 keV. The observed charging characteristics were consistent with predictions of the NASCAP computer model. The use of low electron current density results in a nonlinearity in the sample-potential versus beam-energy characteristic which is attributed to conduction leakage through the sample. Microdischarges were present at relatively low beam energies.

Williamson, W. S.↗