Magnetized Filament Models for Diverging Plasma Lenses
  Spherical plasma lens models are known to suffer from a severe over-pressure
problem, with some observations requiring lenses with central pressures up to
millions of times in excess of the ambient ISM. There are two ways that lens
models can solve the over-pressure problem: a confinement mechanism exists to
counter the internal pressure of the lens, or the lens has a unique geometry,
such that the projected column-density appears large to an observer. This
occurs with highly asymmetric models, such as edge-on sheets or filaments, with
potentially low volume-density. In the first part of this work we investigate
the ability of non-magnetized plasma filaments to mimic the magnification of
sources seen behind spherical lenses and we extend a theorem from gravitational
lens studies regarding this model degeneracy. We find that for plasma lenses,
the theorem produces unphysical charge density distributions. In the second
part of the work, we consider the plasma lens over-pressure problem. Using
magnetohydrodynamics, we develop a non self-gravitating model filament confined
by a helical magnetic field. We use toy models in the force-free limit to
illustrate novel lensing properties. Generally, magnetized filaments may act as
lenses in any orientation with respect to the observer, with the most high
density events produced from filaments with axes near the line of sight. We
focus on filaments that are perpendicular to the line of sight that show the
toroidal magnetic field component may be observed via the lens rotation
measure.
