​X-ray composite image of the Perseus Cluster from the Chandra Telescope.
​Image credit: X-ray: NASA/CXC/SAO/E.Bulbul, et al.

Seminar by Gareth Roberg-Clark

Title of talk: Wave generation and heat flux suppression in astrophysical plasma systems
Seminar by Gareth Roberg-Clark, University of Maryland, USA


Thermal conduction in weakly collisional, weakly magnetized plasmas such as the intracluster medium of galaxy clusters and the solar wind is not fully understood. One possibility is that plasma turbulence at the spatial and temporal scales of the electron gyro-orbits can scatter electrons and inhibit thermal fluxes. Here we present particle-in-cell (PIC) simulations and analytic analysis demonstrating this behavior. In our numerical model two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes oblique whistler waves.
The whistlers grow to large amplitude and resonantly scatter the electrons, strongly suppressing the heat flux. The rate of thermal conduction is controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. Unlike classical (Spitzer) thermal conduction, the resulting steady-state heat flux is largely independent of the thermal gradient. The derived scaling law for thermal conduction has been confirmed in solar wind measurements by Tong et al. (arXiv 2018). We have extended our results to lower beta, which is more relevant for the solar wind and corona. In this regime whistlers gradually become subdominant and the heat flux is mostly regulated by electrostatic double layers, which modify the thermal conduction scaling.
Category Seminar
Location: N6115, seminar room, Fysik Origo, Fysik
Starts: 02 May, 2018, 10:00
Ends: 02 May, 2018, 11:00

Published: Wed 18 Apr 2018.