Electron-scale temperature gradients in kinetic equilibrium: MMS observations and Vlasov-Maxwell solutions

Abstract

For an ideal gas, the notion of thermodynamic equilibrium requires that the system's temperature be spatially uniform. We demonstrate that for a collisionless plasma, kinetic equilibrium can be achieved even in the presence of a temperature gradient. Motivated by recent Magnetospheric Multiscale (MMS) magnetopause observations of thin current layers exhibiting electron-scale temperature gradients, here we present an exact solution to the Vlasov-Maxwell system that accounts for the observed electron temperature gradient and reproduces much of the plasma's spatial variation along one dimension. The current layer in the Vlasov-Maxwell model is self-consistently supported by a prominent crescent-shaped electron velocity distribution that naturally arises due to the temperature transition, which agrees with the electron distribution structures measured by MMS during two asymmetric current layers encountered at the magnetopause.