  The external and independent control of plasma flow velocity shears parallel
and perpendicular to magnetic field lines is realized using segmented
collisionless-plasma sources. Electrostatic ion-cyclotron instabilities are
observed to be suppressed by the perpendicular flow velocity shears, the
suppression physics of which is found to be distinguished into two aspects. On
the other hand, the parallel flow velocity shears are demonstrated to
destabilize the ion-cyclotron instabilities depending on the sign of the
parallel shear in the absence of field-aligned electron drift flow.
