  A two-dimensional dust crystal levitated in the sheath of a modified Gaseous
Electronics Conference (GEC) reference cell is manipulated by heating or
cooling the lower electrode. The dust charge is obtained from top-view pictures
of the crystal using a previously developed analytical model. By assuming a
simple force balance, and measuring the radial confining force, the vertical
electric field profile in the sheath is reconstructed. The dust crystal is
shown to levitate on the plasma side of the Bohm point. Finally, it is shown
that the ion drag plays an important role in the vertical force balance, even
for large dust grains.
