Collaborative Research: Understanding of Presheaths and Sheaths in Plasmas

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AWARD Public Abstract Proposal Title: Collaborative Research: Understanding Sheaths and Pre-Sheaths in PlasmasPrincipal Investigator: Hershkowitz, Noah / Severn, Greg Institution: University of Wisconsin-Madison / University of San DiegoProposal No: CBET- 0903783 / CBET- 0903832 This research addresses basic science questions concerning the sheath-presheath physics in multispecies plasmas that are central to many fields of plasma science and technology, including plasma thrusters, plasma processing, divertors of fusion devices, Langmuir probes, and RF plasmas. After more than 80 years, many important questions associated with sheaths will be addressed for the first time.Proposed experiments are aimed at establishing the basic properties of sheaths and associated presheaths for a variety of situations for which theoretical predictions and assumptions have not yet been verified. Coordinated studies will be carried out at the University of Wisconsin and San Diego University to determine the presheath and sheath plasma potential profiles and the resulting ion velocity distribution functions associated with ion acceleration. Most of the experiments are to be carried out in the laboratory of Prof. Hershkowitz. However, LIF diagnostic development is being carried out on both campuses and is led by Prof. Severn. Plasma parameters will be determined with two or more techniques; e.g., combinations of emissive probes, Ar and Xe metastable ion LIF, Langmuir probes, the phase velocities of ion acoustic waves, pseudo-wave velocities and optical emission spectroscopy. Agreement of several diagnostics is needed because of the invasive or incomplete nature of the diagnostics due to (e.g.) particle depletion by probes and LIF measurements of metastable rather than ground state ions. Experiments will employ hot-filament multi-dipole, capacitive, inductive, and helicon sources currently in operation in our laboratory. Negative ions will be produced by adding O2, SF6, or Cl2 into Ar and Xe plasmas. As noted above, many plasma-based technologies would benefit. The results of the proposed research will be disseminated broadly in the scientific community and industry through publications and conference presentations. The panel considered it likely that the results will be used in plasma physics textbooks and will be widely referenced for years to come. Graduate and undergraduate students will participate in the research, and the experiments used in these investigations will be used in student laboratory courses. The relatively inexpensive tabletop experiments used in these investigations are suited to student laboratory courses, permitting students to perform state-of-the-art experiments.