Nonlocal current-driven heat flow in ideal plasmas

Abstract

Electron heat flux is an important and often dominant mechanism of energy transport in a variety of collisional plasmas in a confined fusion or astrophysical context. While nonlocal conductive heat transport, driven by strong temperature gradients, has been investigated extensively in previous literature, nonlocal regimes of the current-driven heat flow and friction have not received the same attention. In this work, a first-principles reduced kinetic method (RKM) is applied to study nonlocal effects on current-driven transport. In addition to nonlocality due to sharp gradients, sufficiently large currents are found to significantly enhance current-driven heat flux due to a novel nonlocal mechanism, with this enhancement being increasingly prevalent for higher effective ionizations $Z^*$. Introducing the dimensionless number $N_u \equiv \vert \boldsymbol{u}_e - \boldsymbol{u}_i \vert / v_{\text{th},e}$, these enhancements occur for even relatively weak flows $N_u \gtrsim 1/100$, analogously to standard nonlocal effects becoming significant for Knudsen numbers $N_K \gtrsim 1/100$.