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Clemson University

1. Gall, Amy Christina. Inner Shell Atomic Processes in Highly Charged Argon EBIT Plasma Relevant to Astrophysics.

Degree: PhD, Physics and Astronomy, 2019, Clemson University

Astrophysics is a broad and dynamic field that has led to an ever increasing number of incredible discoveries. Just in the past decade or so astrophysicists have detected gravitational waves (and the electromagnetic counterpart) from a neutron star merger, imaged a black hole for the first time, discovered thousands of new planets orbiting stars, and have shown that the expansion of the Universe is accelerating. Many of these discoveries come from new facilities with advanced technologies, an increase in computational capabilities, and creative new analytical techniques. These continued improvements have led to higher quality data that often reveals that our understanding of the processes responsible for the observations is far from complete. It is the field of laboratory astrophysics (experimental and theoretical) that aims to advance our understanding of the underlying processes for more reliable interpretations of astrophysical observations. With this motivation in mind, this work first describes the electron beam ion trap (EBIT), a facility well suited for systematic atomic studies. The EBIT has a nearly mono-energetic electron beam and allows for the injection of a variety of species, including astrophysically relevant elements such as Fe or Ar. Since ions are present almost everywhere in the Universe, and are responsible for much of the measured emission, it is important to note that the tunable electron beam energy can reach up to about 30 keV and is capable of producing basically all charge states of astrophysically relevant elements. The narrow electron beam energy profile allows the user to select the charge state and to an extent the excited state, and is well suited for systematic studies. The EBIT contains a series of electrodes used to manipulate the electron beam and electrostatically trap the ions. The space charge of the electron beam and shape of the trapping electrodes work to radially trap ions. Observation ports are located radially around the trap and are oriented perpendicular to the direction of the electron beam. The non-thermal uni-directional electron beam interacts with stationary ions in the trap. This setup leads to non-statistically populated magnetic sublevels that produce polarized and anisotropic emission, and provides a unique opportunity to study magnetic sublevels which are typically inaccessible in spectroscopic observations. In the second part of this work we take advantage of this capability of the EBIT and report the measurement of the linear polarization of He-like and Li-like Ar transitions. Measurements were taken with two Johann-type crystal spectrometers in different orientations corresponding to the dispersion plane parallel and perpendicular to the electron beam direction. The Li-like transitions result from the resonant dielectronic recombination process while the He-like transitions are produced from electron impact excitation. Our results show a strong positive polarization of the w, j, k, and q transitions (in notation of Gabriel (1972)), and a… Advisors/Committee Members: Endre Takacs, Committee Chair, Chad Sosolik, Marco Ajello, Randall Smith.

Subjects/Keywords: Atomic Physics; Dielectronic Recombination; EBIT; Laboratory Astrophysics; Polarization; Spectroscopy

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APA (6th Edition):

Gall, A. C. (2019). Inner Shell Atomic Processes in Highly Charged Argon EBIT Plasma Relevant to Astrophysics. (Doctoral Dissertation). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/2446

Chicago Manual of Style (16th Edition):

Gall, Amy Christina. “Inner Shell Atomic Processes in Highly Charged Argon EBIT Plasma Relevant to Astrophysics.” 2019. Doctoral Dissertation, Clemson University. Accessed September 19, 2019. https://tigerprints.clemson.edu/all_dissertations/2446.

MLA Handbook (7th Edition):

Gall, Amy Christina. “Inner Shell Atomic Processes in Highly Charged Argon EBIT Plasma Relevant to Astrophysics.” 2019. Web. 19 Sep 2019.

Vancouver:

Gall AC. Inner Shell Atomic Processes in Highly Charged Argon EBIT Plasma Relevant to Astrophysics. [Internet] [Doctoral dissertation]. Clemson University; 2019. [cited 2019 Sep 19]. Available from: https://tigerprints.clemson.edu/all_dissertations/2446.

Council of Science Editors:

Gall AC. Inner Shell Atomic Processes in Highly Charged Argon EBIT Plasma Relevant to Astrophysics. [Doctoral Dissertation]. Clemson University; 2019. Available from: https://tigerprints.clemson.edu/all_dissertations/2446

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