Collaborative Research: Understanding Sheaths and Presheaths in Magnetized and Unmagnetized Plasmas
The common states of matter on Earth are solids, liquids and gases. Putting energy into gases can result in the 4th state of matter known as plasma, which consists of electrically charged particles (electrons and ions, both positive and negative) and neutral atoms and molecules. While uncommon on the Earth, plasma makes up more than 99\% of the visible matter in the universe. Where plasma comes in contact with material boundaries, a thin region near the plasma boundary usually forms to isolate the plasma from the boundary. This thin region is called the plasma sheath. Experiments performed under aimed at improving our understanding of plasma sheaths and associated phenomena as fundamental to understanding all bounded plasmas. Plasma studied in this work are similar to those used in plasma applications such as the etching of semiconducting materials to make computer chips, in plasma space propulsion satellite engines, and used in experimental plasma fusion devices. The majority of experimental studies were carried out at the University of Wisconsin-Madison in close collaboration with Dr. Severn at the University of San Diego (USD), where most of diagnostic development for laser-induced fluorescence (LIF) measurements were carried out. USD is primarily an undergraduate institution. The award made possible outreach activities that promoted engagement of undergraduate students with diverse backgrounds in science, technology, engineering and mathematics (STEM) disciplines. Experiments addressed important questions associated with sheaths and the Bohm Criterion in multiple ion species plasma, many for the first time. In previous work, this collaborative group discovered anomalous sheath edge velocities while testing the Bohm Criterion in two ion species plasma. This effect has now been theoretically explained via the introduction of ion-ion streaming instabilities that led to something now called instability enhanced collisional friction (IEF). As a result, many different aspects of sheath formation must be reevaluated in light of the new theory, and much of our work involved experimental tests of the theory that were performed for the first time. Moreover, there had been no tests of the Bohm Criterion in magnetized plasmas that involved measurements of ion flow. The experiments performed under this award were the first. We found that currently accepted model of the magnetized plasma boundary was not valid. In what follows, a brief overview of salient results will be given.
- Research Organization:
- Prof. Greg Severn University of San Diego
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Contributing Organization:
- Dr. Noah Hershkowitz, Dept. Engineering Physics, University of Wisconsin, Madison, Madison WI USA; Dr. Oliver Schmitz, Dept. Engineering Physics, University of Wisconsin, Madison, Madison WI USA; Dr. KyuSun Chung, Applied Plasma Laboratory, Department of Nuclear Engineering, Hanyang University, Seoul 133-791
- DOE Contract Number:
- SC0014226
- OSTI ID:
- 1575391
- Report Number(s):
- DOE-USD-SC0014226
- Resource Relation:
- Related Information: Refereed Journal articles and Conference Papers1) Chi-Shung Yip; Hershkowitz, N.; Severn, G. (2017). Ion velocity-locking in the neighborhood of virtual cathodes via instability enhanced collisional friction. Plasma Sources Science and Technology. 26 (1), 015008. Status = PUBLISHED; Acknowledgment of Federal Support = Yes ; Peer Reviewed = Yes ; DOI: DOI: 10.1088/0963-0252/26/1/0150082) Chi-Shung Yip; Hershkowitz, N.; Severn, G.; Baalrud, S.D. (2016). Laser-induced fluorescence measurements of argon and xenon ion velocities near the sheath boundary in 3 ion species plasmas. Physics of Plasmas. 23 (5), 050703. Status = PUBLISHED; Acknowledgment of Federal Support = Yes ; Peer Reviewed = Yes ; DOI: DOI: 10.1063/1.49508233) Green, Jonathan; Schmitz, Oliver; Severn, Greg; Winters, Victoria, (2019). Exploiting Zeeman Effect Symmetries to Measure Ion Velocities in Magnetized Plasmas. Measurement Science and Technology. 30 (5), 055202. Status = PUBLISHED; Acknowledgment of Federal Support = Yes ; Peer Reviewed = Yes ; DOI: DOI: 10.1088/1361-6501/ab0e904) Severn, G.; Chi-Shung Yip; Hershkowitz, N.; Baalrud, S.D. (2017). Experimental studies of ion flow near the sheath edge in multiple ion species plasma including argon, xenon and neon. Plasma Sources Science and Technology. 26 (5), 055021. Status = PUBLISHED; Acknowledgment of Federal Support = Yes ; Peer Reviewed = Yes ; DOI: DOI: 10.1088/1361-6595/aa6776Note: for full list of conference papers, see uploaded report.
- Country of Publication:
- United States
- Language:
- English
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