Saturation mechanism of the fluctuation dynamo in supersonic turbulent
  plasmas
  Magnetic fields in several astrophysical objects are amplified and maintained
by a dynamo mechanism, which is the conversion of the turbulent kinetic energy
to magnetic energy. A dynamo that amplifies magnetic fields at scales $<$ the
driving scale of turbulence is known as the fluctuation dynamo. We study the
properties of the fluctuation dynamo in supersonic turbulent plasmas, which is
of relevance to the ISM, structure formation, and lab experiments of
laser-plasma turbulence. Using simulations, we explore the properties of the
exponentially growing and saturated state of the fluctuation dynamo for
subsonic and supersonic turbulence. We confirm that the fluctuation dynamo
efficiency decreases with compressibility. We show that the fluctuation dynamo
generated magnetic fields are spatially intermittent and the level of
intermittency decreases as the field saturates. We find a stronger back
reaction of the magnetic field on the velocity for the subsonic case as
compared to the supersonic case. Locally, we find that the level of alignment
between vorticity and velocity, velocity and magnetic field, and current
density and magnetic field in the saturated stage is enhanced in comparison to
the exponentially growing phase for the subsonic case, but only the current
density and magnetic field alignment is enhanced for the supersonic case. We
show that both the magnetic field amplification (due to weaker stretching of
field lines) and diffusion decreases when the field saturates, but the
diffusion is enhanced relative to amplification. This occurs throughout the
volume in the subsonic turbulence, but primarily in the strong-field regions
for the supersonic case. This leads to the saturation of the fluctuation
dynamo. Overall, both the amplification and diffusion of magnetic fields are
affected and thus a drastic change in either of them is not required for the
saturation. [Abstract abridged]
