CASPERCenter for Astrophysics, Space Physics & Engineering Researchhttps://hdl.handle.net/2104/55012019-01-17T01:48:09Z2019-01-17T01:48:09ZDiscrete stochastic charging of aggregate grainsMatthews, LorinShotorban, BabakHyde, Truell W.https://hdl.handle.net/2104/104692018-11-26T09:03:38Z2018-05-01T00:00:00ZDiscrete stochastic charging of aggregate grains
Matthews, Lorin; Shotorban, Babak; Hyde, Truell W.
Dust particles immersed in a plasma environment become charged through the collection of electrons and ions at random times, causing the dust charge to fluctuate about an equilibrium value. Small grains (with radii less than 1 µm) or grains in a tenuous plasma environment are sensitive to single additions of electrons or ions. Here we present a numerical model that allows examination of discrete stochastic charge fluctuations on the surface of aggregate grains and determines the effect of these fluctuations on the dynamics of grain aggregation. We show that the mean and standard deviation of charge on aggregate grains follows the same trends as those predicted for spheres having an equivalent radius, though aggregates exhibit larger variations from the predicted values. In some plasma environments, these charge fluctuations occur on timescales which are relevant for dynamics of aggregate growth. Coupled dynamics and charging models show that charge fluctuations tend to produce aggregates which are much more linear or filamentary than aggregates formed in an environment where the charge is stationary.
2018-05-01T00:00:00ZTransport properties of disordered 2D complex plasma crystalKostadinova, EvaGuyton, ForestCameron, AdamBusse, KyleLiaw, ConstanzeMatthews, Lorin S.Hyde, Truell W.https://hdl.handle.net/2104/104682018-11-26T09:02:36Z2018-01-01T00:00:00ZTransport properties of disordered 2D complex plasma crystal
Kostadinova, Eva; Guyton, Forest; Cameron, Adam; Busse, Kyle; Liaw, Constanze; Matthews, Lorin S.; Hyde, Truell W.
In this work, we investigate numerically the transport properties of a 2D complex plasma crystal using diffusion of coplanar dust lattice waves. In the limit where the Hamiltonian interactions can be decoupled from the non-Hamiltonian effects, we identify two distinct types of wave transport: Anderson-type delocalization and long-distance excitation. We use a recently-developed spectral approach to evaluate the contribution of the Anderson problem and compare it to the results of the simulation. The benefit of our approach to transport problems is twofold. First, we employ a highly tunable macroscopic hexagonal crystal, which exhibits many-body interactions and allows for the investigation of transport properties at the kinetic level. Second, the analysis of the transport problem in 2D is provided using an innovative spectral approach, which avoids the use of scaling and boundary conditions. The comparison between the analytically predicted and numerically observed wave dynamics allows for the study of important characteristics of this open system. In our simulations, we observe long-distance lattice excitation, which occurs around lattice defects even when the initial perturbation does not spread from the center to the exterior of the crystal. In the decoupled Hamiltonian regime, this many-body effect can be contributed to the dust lattice interaction with the plasma environment.
2018-01-01T00:00:00ZThe magnetic field inside a protoplanetary disk gap opened by planets of different massesCarballido, AugustoMatthews, LorinHyde, Truell W.https://hdl.handle.net/2104/102072018-02-22T09:00:57Z2017-01-01T00:00:00ZThe magnetic field inside a protoplanetary disk gap opened by planets of different masses
Carballido, Augusto; Matthews, Lorin; Hyde, Truell W.
We perform magnetohydrodynamic simulations of protoplanetary disc gaps opened by planets
of various masses, with the aim of calculating the strength of the vertical magnetic field
threading such gaps. We introduce a gravitational potential at the centre of a shearing box to
compute the tidal interaction between the planets and the disc gas, which is turbulent due to
the magnetorotational instability. Two types of simulations are executed: 1) In type ‘Z’, the
initial magnetic field has only a uniform, vertical component, and ten planet masses between
0.66 and 6.64 thermal masses are used; 2) In type ‘YZ’, the initial magnetic field has both
toroidal and vertical components, and five planet masses covering the same mass range are
used. Our results show that, for low planet masses, higher values of the vertical magnetic field
occur inside the gaps than outside, in agreement with the previous work. However, for massive
planets, we find that the radial profiles of the field show dips near the gap centre. The interior
of the Hill sphere of the most massive planet in the Z runs contains more low-plasma β values
(i.e. high magnetic pressure) compared to lower-mass planets. Values of β at a distance of one
Hill radius from each planet show a moderate decrease with planet mass. These results are
relevant for the magnetic structure of circumplanetary discs and their possible outflows, and
may be refined to aid future observational efforts to infer planet masses from high-resolution
polarimetric observations of discs with gaps.
2017-01-01T00:00:00ZDelocalization in infinite disordered two-dimensional lattices of different geometryKostadinova, EvaBusse, KyleEllis, NaokiPadgett, JoshLiaw, ConstanzeMatthews, Lorin S.Hyde, Truell W.https://hdl.handle.net/2104/102062018-02-22T09:00:55Z2017-12-06T00:00:00ZDelocalization in infinite disordered two-dimensional lattices of different geometry
Kostadinova, Eva; Busse, Kyle; Ellis, Naoki; Padgett, Josh; Liaw, Constanze; Matthews, Lorin S.; Hyde, Truell W.
The spectral approach to infinite disordered crystals is applied to anAnderson-type Hamiltonian to demonstrate the existence of extended states for nonzero disorder in 2D lattices of different geometries. The numerical simulations shown prove that extended states exist for disordered honeycomb, triangular, and square crystals. This observation stands in contrast to the predictions of scaling theory, and aligns with experiments in photonic lattices and electron systems. The method used is the only theoretical approach aimed at showing delocalization. A comparison of the results for the three geometries indicates that the triangular and honeycomb lattices experience transition in the transport behavior for similar levels of disorder, which is to be expected from the planar duality of the lattices. This provides justification for the use of artificially prepared triangular lattices as analogues for honeycomb materials, such as graphene. The analysis also shows that the transition in the honeycomb case happens more abruptly compared to the other two geometries, which can be attributed to the number of nearest neighbors.We outline the advantages of the spectral approach as a viable alternative to scaling theory and discuss its applicability to transport problems in both quantum and classical 2D systems.
2017-12-06T00:00:00Z