John E. Foster

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

NEXT: NASA's Evolutionary Xenon Thruster

NASA’s Glenn Research Center has been selected to lead development of NASA’s Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster (EPT) that inherits the knowledge gained through the NSTAR thruster that successfully propelled the Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The EPT concept under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster, while maintaining a relatively-small volume. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm engine, while incorporating new technology where warranted to extend the power and throughput capability.

Observations of electric discharge streamer propagation and capillary oscillations on the surface of air bubbles in water

The propagation of electric discharge streamers inside bubbles in liquids is of interest for the remediation of toxins in water and plasma-based surgical instruments. The manner of streamer propagation has an important influence on the production of reactive species that are critical to these applications. Streamer propagation along the surface of electrode-attached bubbles of air in water, previously predicted by numerical simulations, has been experimentally imaged using a fast frame-rate camera. The successive pulsing of the streamer discharge inside the bubbles produced oscillations along the air‐water interface. Subsequent streamers were observed to closely follow surface distortions induced by such oscillations. The oscillations likely arise from the non-uniform perturbation of the bubble driven by the electric field of the streamer and were found to be consistent with Kelvin’s equation for capillary oscillations. For a narrow range of applied voltage pulse frequencies, the oscillation amplitude increased over several pulse periods indicating, potentially, resonant behaviour. We also observed coupling between bubbles wherein oscillations in a second bubble without an internal discharge were induced by the presence of a streamer in a fixed bubble. (Some figures in this article are in colour only in the electronic version)

Next: NASA's Evolutionary Xenon Thruster development status

NASA’s Glenn Research Center (GRC) is leading the development of NASA’s Evolutionary Xenon Thruster (NEXT) system. The central feature of the NEXT system is an electric propulsion thruster that inherits the knowledge gained through the NSTAR thruster that successfully propelled the Deep Space 1 to asteroid Braille and comet Borrelly, while significantly increasing the thruster power level and making improvements in performance parameters associated with NSTAR. The thruster under development has a 40 cm beam diameter, twice the effective area of the Deep-Space 1 thruster. It incorporates mechanical features and operating conditions to maximize the design heritage established by the flight NSTAR 30 cm thruster, while incorporating new technology where warranted to extend the power and throughput capability. To date three engineering-model thrusters have been manufactured at NASA GRC, and performance, wear, vibration, and integration testing of these thrusters is underway.

The High Power Electric Propulsion (HiPEP) Ion Thruster

John E. Foster, Tom Haag, and Michael PattersonGlenn Research Center, Cleveland, OhioGeorge J. Williams, Jr.Ohio Aerospace Institute, Brook Park, OhioJames S. SoveyAlpha-Port, Inc., Cleveland, OhioChristian CarpenterQSS Group, Inc., Cleveland, OhioHani Kamhawi, Shane Malone, and Fred ElliotGlenn Research Center, Cleveland, Ohio

Perspectives on the Interaction of Plasmas With Liquid Water for Water Purification

Plasma production or plasma injection in liquid water affords one the opportunity to nonthermally inject advanced oxidation processes into water for the purpose of purification or chemical processing. Such technology could potentially revolutionize the treatment of drinking water, as well as current methods of chemical processing through the elimination of physical catalysts. Presented here is an overview of current water treatment technology, its limitations, and the future, which may feature plasma-based advanced oxidation techniques. As such, this field represents an emerging and active area of research. The role that plasma-driven water chemistry can play in addressing emerging threats to the water supply is discussed using case study examples. Limitations of conventional plasma injection approaches include limited throughput capacity, electrode erosion, and reduced process volume. At the University of Michigan, we are investigating two potential approaches designed to circumvent such issues. These include direct plasma injection using an underwater DBD plasma jet and the direct production of plasmas in isolated underwater bubbles via a pulsed electric field. These approaches are presented here, along with the results.

Plasma-based water purification: Challenges and prospects for the future

Freshwater scarcity derived from seasonal weather variations, climate change, and over-development has led to serious consideration for water reuse. Water reuse involves the direct processing of wastewater for either indirect or directly potable water reuse. In either case, advanced water treatment technologies will be required to process the water to the point that it can be reused in a meaningful way. Additionally, there is growing concern regarding micropollutants, such as pharmaceuticals and personal care products, which have been detected in finished drinking water not removed by conventional means. The health impact of these contaminants in low concentration is not well understood. Pending regulatory action, the removal of these contaminants by water treatment plants will also require advanced technology. One new and emerging technology that could potentially address the removal of micropollutants in both finished drinking water as well as wastewater slated for reuse is plasma-based water purificati...

NEXT multi-thruster array test -Engineering demonstration

A multi-thruster array test was executed at NASA Glenn Research Center, focusing on the characterization of individual thruster, and array, performance and behavior – as affected by the simultaneous operation of multiple ion thrusters; a key step in development of the NEXT ion propulsion system. The subject of this characterization effort was a four engineering model NEXT thruster array in a 3+1 flight-representative configuration where one thruster was dormant (a spare). This test was executed concurrent with detailed plasma environments and plume measurements documented elsewhere. The array was operated over a broad range of conditions including the simultaneous firing of 3 thrusters at 20.6 kW total input power, yielding a total thrust of about 710 mN, at 4190 seconds specific impulse and approximately 71 percent efficiency. Major findings from a series of tests include: the performance observed for a thruster during operation in an array configuration appears to be consistent with that measured during singular thruster operation with no apparent deleterious interactions; and, operation of 1 neutralizer to neutralize 2-or-more thruster beams appears to be a potentially viable fault-recovery mode, and viable system architecture with significant system performance advantages. Overall, the results indicating single thruster operations are generally independent of array configuration have potentially significant implications with respect to testing requirements and architectural flexibility for multi-thruster systems.

Underwater operation of a DBD plasma jet

A plasma jet produced in water using a submerged ac excited electrode in a coaxial dielectric barrier discharge configuration was studied. Plasma jet formation was found to occur only while the source was submerged. Plasma jet operation was characterized with and without gas flow. It was found that over 60% of the discharge power was deposited into the water and did not vary appreciably with excitation frequency. Presumably the remaining power fraction went into excitation, ionization and local electrode heating. Emission spectra of the jet revealed nitrogen, hydrogen, hydroxyl and oxygen emission lines. Operation of the plasma jet in water containing the oxidation‐reduction indicator methylene blue dye resulted in a marked clearing of the water as observed visually and with a spectrophotometer, suggesting plasma-induced chemical reactivity. (Some figures in this article are in colour only in the electronic version)

Very-near-field plume study of a 1.35 kW SPT-100

Ion current density and electron number density profiles were measured in the very-nearfield plume of a 1.35 kW stationary plasma thruster (SPT-100) loaned from Space Systems/Loraland Fakel Enterprises. In order to take these measurements without significantly disturbing plasma flow while data were collected, a small Faraday probe and a single Langmuir probe were constructed and used with high-speed electronics for fast spatial sweeps. The data showed that there were distinct peaks in ion current density and electron number density related to the position of the thruster discharge chamber exit in the very-nearfield plume. These peaks decreased and broadened as the axial position from the thruster exit increased. The Faraday probe data showed that a diverging annular ion beam came out of the discharge chamber. The inner boundary converged at or near 100 mm downstream of the exit plane. The Langmuir probe data gave insight to the competing effects between magnetic field confinement and diffusive processes.