Detailed structure and dynamics in particle-in-cell simulations of the lunar wake

Birch, Paul C.; Chapman, Sandra C.

doi:10.1063/1.1398570

Cited by 42 publications

(69 citation statements)

References 16 publications

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“…Given that the mean energy at each position defines the particle velocity, the shape of the ion wake is due to the fact that for positive and negative y, the ions are accelerated and decelerated, respectively. Similar wake structures in ion spectrograms have been observed at the moon Ogilvie et al (1996), and have been reproduced at various lunar-wake simulations (Kallio, 2005;Birch and Chapman, 2001;Travnicek et al, 2005).…”

Section: Kinetic Effects and Phase-space Diagramssupporting

confidence: 60%

“…Through a fully kinetic approach, such as the one by Birch and Chapman (2001), high frequency or small scale phenomena (down to the Debye length, ∼20-30 m for Rhea) could also be studied. In particular, effects resulting from the fast expansion of electrons into the wake and the deviation from charge neutrality could play a significant role in the plasma dynamics downstream of Rhea.…”

Section: Discussionmentioning

confidence: 99%

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Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

et al. 2008

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Abstract. Rhea's magnetospheric interaction is simulated using a three-dimensional, hybrid plasma simulation code, where ions are treated as particles and electrons as a massless, charge-neutralizing fluid. In consistency with Cassini observations, Rhea is modeled as a plasma absorbing obstacle. This leads to the formation of a plasma wake (cavity) behind the moon. We find that this cavity expands with the ion sound speed along the magnetic field lines, resulting in an extended depletion region north and south of the moon, just a few Rhea radii (R Rh ) downstream. This is a direct consequence of the comparable thermal and bulk plasma velocities at Rhea. Perpendicular to the magnetic field lines the wake's extension is constrained by the magnetic field. A magnetic field compression in the wake and the rarefaction in the wake sides is also observed in our results. This configuration reproduces well the signature in the Cassini magnetometer data, acquired during the close flyby to Rhea on November 2005. Almost all plasma and field parameters show an asymmetric distribution along the plane where the corotational electric field is contained. A diamagnetic current system is found running parallel to the wake boundaries. The presence of this current system shows a direct corelation with the magnetic field configuration downstream of Rhea, while the resulting j×B forces on the ions are responsible for the asymmetric structures seen in the velocity and electric field vector fields in the equatorial plane. As Rhea is one of the many plasma absorbing moons of Saturn, we expect that this case study should be relevant for most lunar-type interactions at Saturn.

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Section: Kinetic Effects and Phase-space Diagramssupporting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

et al. 2008

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“…The process of plasma expansion into a vacuum has a lot of details, and instabilities that can form (Birch and Chapman, 2001). Also, the region near the lunar surface probably has strong electric fields, and charge separation effects (Farrell et al, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…However, there are many kinetic processes that cannot be described by fluid models, e.g., the non-Maxwellian particle populations in the wake region, so particle models should capture more of the physical processes. An approximation of the refill of the lunar wake is the general one-dimensional problem where plasma expands into a vacuum (Widner et al, 1971;Samir et al, 1983;Mora, 2003), and such models have specifically been applied to the refill of the lunar wake (Farrell et al, 1998;Birch and Chapman, 2001). A nice property of such models is that even if they are one-dimensional, they can to some degree approximate a two-dimensional model of the lunar wake, where time corresponds to distance downstream the wake, i.e., the one-dimensional model is applied perpendicular to the solar wind flow and convects with the flow.…”

Section: Introductionmentioning

confidence: 99%

The interaction between the Moon and the solar wind

et al. 2012

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We study the interaction between the Moon and the solar wind using a three-dimensional hybrid plasma solver. The proton fluxes and electromagnetical fields are presented for typical solar wind conditions with different magnetic field directions. We find two different wake structures for an interplanetary magnetic field that is perpendicular to the solar wind flow, and for one that is parallell to the flow. The wake for intermediate magnetic field directions will be a mix of these two extreme conditions. Several features are consistent with a fluid interaction, e.g., the presence of a rarefaction cone, and an increased magnetic field in the wake. There are however several kinetic features of the interaction. We find kinks in the magnetic field at the wake boundary. There are also density and magnetic field variations in the far wake, maybe from an ion beam instability related to the wake refill. The results are compared to observations by the WIND spacecraft during a wake crossing. The model magnetic field and ion velocities are in agreement with the measurements. The density and the electron temperature in the central wake are not as well captured by the model, probably from the lack of electron physics in the hybrid model.

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“…To model the solar wind wake behind the Moon, extensive hybrid simulations have previously been carried out using simplified (typically fluid) electron models [3][4][5][6][7][8] , but simulations with kinetic electrons [9][10][11][12][13] have identified important phenomena not captured by such hybrid treatments. In particular, it was recently shown in kinetic 1D simulations 13 that the lunar wake may be unstable much closer to the Moon than expected from hybrid simulations.…”

Section: Introductionmentioning

confidence: 99%

The electron forewake: Shadowing and drift-energization as flowing magnetized plasma encounters an obstacle

Haakonsen

Hutchinson

2015

Physics of Plasmas

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Flow of magnetized plasma past an obstacle creates a traditional wake, but also a forewake region arising from shadowing of electrons. The electron forewakes resulting from supersonic flows past insulating and floating-potential obstacles are explored with 2D electrostatic particle-in-cell simulations, using a physical ion to electron mass ratio. Drift-energization is discovered to give rise to modifications to the electron velocitydistribution, including a slope-reversal, providing a novel drive of forewake instability. The slope-reversal is present at certain locations in all the simulations, and appears to be quite robustly generated. Wings of enhanced electron density are observed in some of the simulations, also associated with drift-energization. In the simulations with a floating-potential obstacle, the specific potential structure behind that obstacle allows fast electrons to cross the wake, giving rise to a more traditional shadowing-driven two-stream instability.Fluctuations associated with such instability are observed in the simulations, but this instability-mechanism is expected to be more sensitive to the plasma parameters than that associated with the slope-reversal.

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Detailed structure and dynamics in particle-in-cell simulations of the lunar wake

Cited by 42 publications

References 16 publications

Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

The interaction between the Moon and the solar wind

The electron forewake: Shadowing and drift-energization as flowing magnetized plasma encounters an obstacle

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