A toner gating apparatus for supplying toner through an aperture to a gas channel
having a propellant stream. The toner gating apparatus has a traveling wave grid
having electrodes. A first gating electrode is located proximate a first side of
the aperture. A second gating electrode is located proximate a second side of the
aperture. A third gating electrode is located in the gas channel. A first voltage
source having a first phase is connected to both the first gating electrode and
a first electrode of the travelling wave grid. A second voltage source having a
second phase is connected to both the second gating electrode and a second electrode
of the travelling wave grid. A third voltage source having a third phase is connected
to both the third gating electrode and a third electrode of the travelling wave grid.