PIC simulations of stable surface waves on a subcritical fast magnetosonic shock front

Dieckmann, M. E. and Huete, C. and Cobos, F. and Bret, A. and Folini, D. and Eliasson, B. and Walder, R. (2023) PIC simulations of stable surface waves on a subcritical fast magnetosonic shock front. Physica Scripta, 98 (9). 095603. ISSN 0031-8949 (https://doi.org/10.1088/1402-4896/ace801)

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Abstract

We study with particle-in-cell (PIC) simulations the stability of fast magnetosonic shocks. They expand across a collisionless plasma and an orthogonal magnetic field that is aligned with one of the directions resolved by the 2D simulations. The shock speed is 1.6 times the fast magnetosonic speed when it enters a layer with a reduced density of mobile ions, which decreases the shock speed by up to 15\% in 1D simulations. In the 2D simulations, the density of mobile ions in the layer varies sinusoidally perpendicularly to the shock normal. We resolve one sine period. This variation only leads to small changes in the shock speed evidencing a restoring force that opposes a shock deformation. As the shock propagates through the layer, the ion density becomes increasingly spatially modulated along the shock front and the magnetic field bulges out where the mobile ion density is lowest. The perturbed shock eventually reaches a steady state. Once it leaves the layer, the perturbations of the ion density and magnetic field oscillate along its front at a frequency close to the lower-hybrid frequency; the shock is mediated by a standing wave composed of obliquely propagating lower-hybrid waves. We perform three 2D simulations with different box lengths along the shock front. The shock front oscillations are aperiodically damped in the smallest box with the fastest variation of the ion density, strongly damped in the intermediate one, and weakly damped in the largest box. The shock front oscillations perturb the magnetic field in a spatial interval that extends by several electron skin depths upstream and downstream of the shock front and could give rise to Whistler waves that propagate along the shock's magnetic field overshoot. Similar waves were observed in hybrid and PIC simulations and by the MMS satellite mission.

  • Item type:Article
    ID code:86192
    Dates:
    Date
    Event
    1 September 2023
    Published
    17 July 2023
    Published Online
    17 July 2023
    Accepted
    7 May 2023
    Submitted
    Subjects:Science > Physics > Plasma physics. Ionized gases
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:20 Jul 2023 09:48
    Last modified:11 Apr 2024 02:44
    URI:https://strathprints.strath.ac.uk/id/eprint/86192
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