Congratulations to Marlene Patino for a successful thesis defense!

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“Plasma Interparticle and Particle-Wall Interactions”

Abstract: Plasma inter-species interactions and plasma-material interactions must be understood to advance the rapidly growing implementation of partially-ionized plasma devices (such as space electric propulsion) and for applications such as fusion and high-power communication devices. Of particular importance are ion-atom collisions occurring within the plasma bulk, and secondary electron emission from plasma-facing materials at the plasma edge.

Collisions between fast ions and slow atoms produce slow charge-exchange ions that are important to understanding the performance and behavior of many plasma devices. For example, in space electric propulsion these charge-exchange ions can produce deleterious effects to spacecraft surfaces and components. The first half of this talk will present results from a simple, well-characterized experiment that carefully measures the effects of high energy xenon ions impacting xenon atoms. These data provide canonical data to which theories and models can be validated. By comparing these data to semi-analytical and fully-computational models, it is found that many existing models do not properly simulate charge-exchange collisions.

The second half of this talk will discuss the interaction of plasma electrons with plasma-confining walls in plasma thrusters, magnetic confinement fusion, and other plasma devices. These interactions cause secondary electron emission that can adversely affect plasma and device performance (e.g., large plasma energy loss to the wall). This talk will present results of the secondary electron emission properties of graphite (used for tokamaks, ion thrusters, and traveling wave tubes) and tungsten (the most promising material for future tokamaks such as ITER) for a wide range of incident electron energies and angles. In particular, secondary electron emission from nanostructured tungsten fuzz was measured and found to be significantly reduced compared to smooth tungsten. This has important implications for fusion devices with plasma facing tungsten components where fuzz may be naturally generated. Thus, measurements show that the self-generation of a low SEE surface such as tungsten fuzz in a tokamak can be desirable for improved performance.

Bio: Marlene Patino is a Ph.D. candidate in the UCLA MAE Department. She is part of the UCLA Plasma & Space Propulsion Laboratory and works with Prof. Richard Wirz. She received her B.S. and M.S. degrees in Aerospace Engineering from UCLA in 2010 and 2012, respectively. Her doctoral research is done in collaboration with the Jet Propulsion Laboratory and Princeton Plasma Physics Laboratory, and has been funded through the Air Force Office of Scientific Research, UCLA Eugene Cota-Robles Fellowship, DOE Office of Science Graduate Student Research Award, and the UCLA Dissertation Year Fellowship.