A phase-shift-periodic parallel boundary condition for low-magnetic-shear scenarios

Plasma Physics and Controlled Fusion IOP Publishing 65:1 (2022) 15016

Authors:

DA St-Onge, Michael Barnes, FI Parra

Abstract:

We formulate a generalized periodic boundary condition as a limit of the standard twist-and-shift parallel boundary condition that is suitable for simulations of plasmas with low magnetic shear. This is done by applying a phase shift in the binormal direction when crossing the parallel boundary. While this phase shift can be set to zero without loss of generality in the local flux-tube limit when employing the twist-and-shift boundary condition, we show that this is not the most general case when employing periodic parallel boundaries, and may not even be the most desirable. A non-zero phase shift can be used to avoid the convective cells that plague simulations of the three-dimensional Hasegawa–Wakatani system, and is shown to have measurable effects in periodic low-magnetic-shear gyrokinetic simulations. We propose a numerical program where a sampling of periodic simulations at random pseudo-irrational flux surfaces are used to determine physical observables in a statistical sense. This approach can serve as an alternative to applying the twist-and-shift boundary condition to low-magnetic-shear scenarios, which, while more straightforward, can be computationally demanding.

Proton Imaging of High-Energy-Density Laboratory Plasmas

(2022)

Authors:

Derek B Schaeffer, Archie FA Bott, Marco Borghesi, Kirk A Flippo, William Fox, Julien Fuchs, Chikang Li, Hye-Sook Park, Fredrick H Seguin, Petros Tzeferacos, Louise Willingale

Black Hole Binary Formation in AGN Discs: From Isolation to Merger

ArXiv 2212.06133 (2022)

Authors:

Connar Rowan, Tjarda Boekholt, Bence Kocsis, Zoltán Haiman

An analytical form of the dispersion function for local linear gyrokinetics in a curved magnetic field

ArXiv 2212.02654 (2022)

Authors:

PG Ivanov, T Adkins

On the Jacobi capture origin of binaries with applications to the Earth-Moon system and black holes in galactic nuclei

Monthly Notices of the Royal Astronomical Society Oxford University Press 518:4 (2022) 5653-5669

Authors:

Tjarda Boekholt, Connar Rowan, Bence Kocsis

Abstract:

Close encounters between two bodies in a disc often result in a single orbital deflection. However, within their Jacobi volumes, where the gravitational forces between the two bodies and the central body become competitive, temporary captures with multiple close encounters become possible outcomes: a Jacobi capture. We perform three-body simulations in order to characterize the dynamics of Jacobi captures in the plane. We find that the phase space structure resembles a Cantor-like set with a fractal dimension of about 0.4. The lifetime distribution decreases exponentially, while the distribution of the closest separation follows a power law with index 0.5. In our first application, we consider the Jacobi capture of the Moon. We demonstrate that both tidal captures and giant impacts are possible outcomes. The impact speed is well approximated by a parabolic encounter, while the impact angles follow that of a uniform beam on a circular target. Jacobi captures at larger heliocentric distances are more likely to result in tidal captures. In our second application, we find that Jacobi captures with gravitational wave dissipation can result in the formation of binary black holes in galactic nuclei. The eccentricity distribution is approximately superthermal and includes both prograde and retrograde orientations. We conclude that dissipative Jacobi captures form an efficient channel for binary formation, which motivates further research into establishing the universality of Jacobi captures across multiple astrophysical scales.