Fluctuation dynamo in a weakly collisional plasma
In plain words
In hot, thin gas such as that between galaxies, turbulence should stretch and amplify weak magnetic fields. Because particles rarely collide there, the usual fluid theory fails, and how strong the field gets is uncertain.
Precise statement
In a plasma whose ion mean free path exceeds the turbulence scale (as in the intracluster medium), pressure anisotropy and mirror and firehose instabilities modify the effective viscosity. Determine the critical magnetic Reynolds number, the growth rate and the saturated field strength relative to equipartition for the fluctuation dynamo, from 3D kinetic or hybrid simulations, and whether near-equipartition fields arise within a cluster age.
What would settle it
Converged 3D kinetic simulations with an analytic saturation model, consistent with Faraday-rotation field estimates in clusters.
Status in the literature
Hybrid-kinetic simulations since 2016 show the dynamo operates in weakly collisional plasma; saturation level and scale remain debated.