  We consider the radial transport of test particles due to the ExB drift
motion in the guiding center approximation. Using an explicit expression to
modify the electrostatic potential, we show that it is possible to construct a
transport barrier which suppresses radial transport. We propose an algorithm
for the implementation of this local modification computed from an
electrostatic potential known on a spatio-temporal grid. The number of
particles which escape the inner region defined by the barrier measures the
efficiency of the control. We show that the control is robust by showing a
significant reduction of radial transport, when applied with a reduced number
of probes aligned on a circle.
