  We investigate the crescent-shaped dust trap in the transition disk, Oph IRS
48, using well-resolved (sub)millimeter polarimetric observations at ALMA Band
7 (870 $\mu$m). The dust polarization map reveals patterns consistent with dust
scattering-induced polarization. There is a relative displacement between the
polarized flux and the total flux, which holds the key to understanding the
dust scale heights in this system. We model the polarization observations,
focusing on the effects of dust scale heights. We find that the interplay
between the inclination-induced polarization and the polarization arising from
radiation anisotropy in the crescent determines the observed polarization; the
anisotropy is controlled by the dust optical depth along the midplane, which
is, in turn, determined by the dust scale height in the vertical direction. We
find that the dust grains can neither be completely settled nor well mixed with
the gas. The completely settled case produces little radial displacement
between the total and polarized flux, while the well-mixed case produces an
azimuthal pattern in the outer (radial) edge of the crescent that is not
observed. Our best model has a gas-to-dust scale height ratio of 2, and can
reproduce both the radial displacement and the azimuthal displacement between
the total and polarized flux. We infer an effective turbulence $\alpha$
parameter of approximately $0.0001-0.005$. The scattering-induced polarization
provides insight into a turbulent vortex with a moderate level of dust settling
in the IRS 48 system, which is hard to achieve otherwise.
