Nonlocal current-driven heat flow in ideal plasmas

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 Letter, a first-principles reduced kinetic method 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 Nᵤ≡|uₑ-uᵢ|/vth,e, these enhancements occur for even relatively weak flows Nᵤ≳1/100, analogously to standard nonlocal effects becoming significant for Knudsen numbers NK≳1/100.