  A major unexplained feature of the solar atmosphere is the accumulation of
magnetic shear, in the form of filament channels, at photospheric polarity
inversion lines (PILs). In addition to free energy, this shear also represents
magnetic helicity, which is conserved under reconnection. In this paper, we
address the problem of filament channel formation and show how they acquire
their shear and magnetic helicity. The results of 3D simulations using the
Adaptively Refined Magnetohydrodynamics Solver (ARMS) are presented that
support the model of filament channel formation by magnetic helicity
condensation developed by \citet{Antiochos13}. We consider the supergranular
twisting of a quasi-potential flux system that is bounded by a PIL and contains
a coronal hole (CH). The magnetic helicity injected by the small-scale
photospheric motions is shown to inverse-cascade up to the largest allowable
scales that define the closed flux system: the PIL and the CH. This process
produces field lines that are both sheared and smooth, and are sheared in
opposite senses at the PIL and the CH. The accumulated helicity and shear flux
are shown to be in excellent quantitative agreement with the
helicity-condensation model. We present a detailed analysis of the simulations,
including comparisons of our analytical and numerical results, and discuss
their implications for observations.
