  We perform experiments in the Large Plasma Device (LAPD) at the University of
California, Los Angeles, studying how different end-electrode biasing schemes
modify the radial potential profile in the machine. We impose biasing profiles
of different polarities and gradient signs on a set of five concentric
electrodes placed 12 m downstream from the plasma source. We find that imposing
concave-down profiles (negative potential radial gradient) on the electrodes
create radial potential profiles halfway up the plasma column that are
comparable to those imposed on the electrodes, regardless of the biasing
polarity. On the other hand, imposing concave-up profiles (positive potential
radial gradient) leads to non-monotonic radial potential profiles. This
observation can be explained by the current drawn through the electrodes and
the parallel plasma resistivity, highlighting their important role in
controlling the rotation of plasma. Concave-down plasma potential profiles,
obtained by drawing electrons on the axis, are predicted to drive azimuthal
drift velocities that can approach significant fractions of the ion sound speed
in the central region of the plasma column.
