Electrical Resistivity of Collisionless, High-Beta Plasmas

The characteristic reversal scale of amplified magnetic fields during several stages of the fluctuation dynamo is set by the plasma resistivity. In weakly collisional high-beta plasmas, such as in the intracluster medium of galaxy clusters, the nature of this resistivity is likely to be influenced by Larmor-scale kinetic instabilities (firehose, mirror) that are excited by flow-driven pressure anisotropies. The magnetic structures created by these instabilities scatter and trap particles, modifying the plasma resistivity in a way that depends upon extrinsic quantities such as the magnetic-field strength. Using particle-in-cell simulations and scaling arguments, we investigate the changes in plasma resistivity caused by these micro-instabilities. By driving a current through the perturbed plasma, we solve the high-beta collisionless version of the Spitzer-Haerm problem. Our results can be implemented within fluid or hybrid-kinetic treatments to improve the fidelity of large-scale dynamo simulations.