arXiv subjects

Nicholas Mitchell

Publications and source records attributed to Nicholas Mitchell.

4 recordsLinked to original sources

arXiv2026

Impact of ion-electron collisions on nonlocal ion heat conduction, viscous stress, and diffusion

By applying a first-principles reduced kinetic method, this work demonstrates the impact of ion-electron collisions on ion transport for strongly inhomogeneous plasmas in the nonlocal regime, where collisionality is insufficient to enforce local thermal equilibrium due to sharp gradients. Ion heat conduction and viscous stress in both unmagnetized and magnetized plasmas are considered, as well as inter-species diffusion in multi-species plasmas. Most notably, even for equal ion and electron temperatures, ion-electron collisions are found to substantially modify the peak nonlocal heat flow, whereas nonlocal preheats are strongly suppressed since streaming suprathermal particles are further out in the tail of the cold ion distribution where ion-electron collisions become dominant.

physics.plasm-ph↗

arXiv2026

A First-Principles Closure for Nonlocal Magnetized Transport

A reduced kinetic method (RKM) for describing nonlocal transport in magnetized plasmas is derived from first principles and considered in a 1D3V geometry. Unlike standard nonlocal closures, this RKM uses the Fokker-Planck collision operator, therefore local transport results are naturally reproduced for small Knudsen number. An inhibited peak heat flux and preheat of the conductive heat flux are observed, which are expected from physical arguments and previous kinetic studies. Nonlocal behavior of other transport fluxes, namely the Righi-Leduc, Peltier, Ettingshausen, Nernst, thermal force, friction, cross friction, viscous stress, and gyroviscous stress terms are also demonstrated. Neglecting the nonlinear component of the Fokker-Planck collision operator is justified a posteriori. An especially computationally efficient and analytically simpler version of the RKM is presented.

physics.plasm-ph↗

arXiv2025

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 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 $N_K \gtrsim 1/100$.

physics.plasm-ph↗

arXiv2024

A reduced kinetic method for investigating non-local ion heat transport in ideal multi-species plasmas

A reduced kinetic method (RKM) with a first-principle collision operator is introduced in a 1D2V planar geometry and implemented in a computationally inexpensive code to investigate non-local ion heat transport in multi-species plasmas. The RKM successfully reproduces local results for multi-species ion systems and the important features expected to arise due to non-local effects on the heat flux are captured. In addition to this, novel features associated with multi-species, as opposed to single species, case are found. Effects of non-locality on the heat flux are investigated in mass and charge symmetric and asymmetric ion mixtures with temperature, pressure, and concentration gradients. In particular, the enthalpy flux associated with diffusion is found to be insensitive to sharp pressure and concentration gradients, increasing its significance in comparison to the conductive heat flux driven by temperature gradients in non-local scenarios. The RKM code can be used for investigating other kinetic and non-local effects in a broader plasma physics context. Due to its relatively low computational cost it can also serve as a practical non-local ion heat flux closure in hydrodynamic simulations or as a training tool for machine learning surrogates.

physics.plasm-ph↗