Physics of cosmic plasmas from high angular resolution X-ray imaging of galaxy clusters

Galaxy clustersare massive dark matter-dominated systems filled with X-ray emitting, optically thin plasma. Their large size and relative simplicity (at least as astrophysicalobjects go) make them a unique laboratory to measure some of the interesting plasma properties that are inaccessible by other means but fundamentally important for understanding and modeling many astrophysicalphenomena -- from solar flaresto black hole accretion to galaxy formation and the emergence of the cosmological Large Scale Structure. While every cluster astrophysicist is eagerly anticipating the direct gas velocity measurements from the forthcoming microcalorimeters onboard XRISM, Athena and future missions such as Lynx, a number of those plasma properties can best be probed by high-resolution X-ray imaging of galaxy clusters. Chandra has obtained some trailblazing results, but only grazed the surface of such studies. In this white paper, we discuss why we need arcsecond-resolution, high collecting area, low relative background X-ray imagers (with modest spectral resolution), such as the proposed AXIS and the imaging detector of Lynx.