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This theoretical study examines weakly collisional plasmas using an advanced 16-moment fluid model that includes heat flux dynamics. The researchers discovered a new type of linear perturbation characterized by a conserved thermo-mechanic invariant—a time-independent structure coupling heat fluxes, velocity, and magnetic field that does not exist in standard models. This invariant reveals a previously unknown stationary behavior in collisionless plasmas, featuring fixed relationships between thermal, kinetic, and magnetic field perturbations that favor localized, filamentary structures.
Why it matters
Understanding these newly identified plasma structures could improve predictions of space plasma behavior and magnetic confinement in fusion reactors. The discovery challenges existing models by demonstrating that heat flux dynamics fundamentally alter plasma behavior in ways not captured by conventional approaches.
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arXiv:2410.20002v3 Announce Type: replace
Abstract: We investigate linear perturbations of an incompressible, weakly collisional, anisotropic plasma in the low frequency limit using an extended 16-moment fluid description that retains parallel and perpendicular heat fluxes. We identify a new class of linear perturbations associated with a conserved thermo-mechanic invariant, a time independent, aperiodic structure involving coupled perturbations of heat fluxes, velocity, and magnetic field. In the standard CGL limit, where heat fluxes are neglected, no direct analogue of this invariant exists. Retaining heat flux dynamics alters the linear structure of the system promoting third order velocity moments to autonomous variables and gives rise to a thermo-mechanic mode with coupled thermal, kinetic, and magnetic components. The associated perturbations are inherently localized, favoring compact, filamentary aperiodic structures. The thermo-mechanic invariant reveals a previously unexplored stationary sector of collisionless anisotropic plasma dynamics, characterized by a fixed algebraic polarization that enforces time independent relations among the relevant perturbation fields.
Source: A conserved thermo-mechanic invariant in extended fluid description of collisionless plasmas