  Galaxy clusters are massive dark matter-dominated systems filled with X-ray
emitting, optically thin plasma. Their large size and relative simplicity (at
least as astrophysical objects 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 astrophysical
phenomena -- from solar flares to 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.
