Award Date

May 2023

Degree Type


Degree Name

Master of Science (MS)


Physics and Astronomy

First Committee Member

Zhaohuan Zhu

Second Committee Member

Rebecca Martin

Third Committee Member

Daniel Proga

Fourth Committee Member

Pengtao Sun

Number of Pages



Rings are one of the most ubiquitous substructures observed in protoplanetary disks. They are known to be a robust site for planetesimal formation; thus we look for mechanisms that can originate stable rings. From chemical modelling of snow lines, we expect a bump in the Ambipolar Diffusion (AD) Elssaser number (Am) in the radial direction. We use the Athena++ code to model the non-ideal Magentohydrodynamics (MHD) behavior of an Am bump. We explore a parameter space of Gaussian bumps with Am = 5, 1, 0.5 peak strength and σ = 0.25, 1, 5. The Gaussian profile is inserted into the local shearing box MHD model originally run by Hawley et al. (1995). We run both positive and inverted profile cases to 100 orbits, in an 8H × 8H × 1H box. A variety of Am profiles are capable of concentrating gas up to 2.5 × ρ0 (initial density), beyond zonal flows. We note magnetic flux is concentrated in areas of low gas density. σ = 0.25 Gaussians are inconsistent and can exhibit ideal MHD. In the case of a weak overall magnitude of AD, but a non-flat profile, zonal flows are disrupted. The gas density bumps driven by AD are sufficient to trap particles, and therefore an Am bump can trigger ring formation. We also suggest that zonal flows may be fragile to non-flat Am. The Am − ρ relationship in Bai & Stone (2011) is shown to be accurate to within 30% for all but the σ = 0.25 runs, but could be improved upon.


Ambipolar Diffusion; Athena++; Magnetohydrodynamics; Non-Ideal MHD; Proto-Planetary Disks


Astrophysics and Astronomy | Other Physics | Physics

Degree Grantor

University of Nevada, Las Vegas




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