An apparatus and method for scavenging etchant species from a plasma formed of etchant gas prior to the etchant gas entering a primary processing chamber of a plasma reactor. There is at least one scavenging chamber, each of which is connected at an inlet thereof to an etchant gas source and at an outlet thereof to a gas distribution device of the primary processing chamber. Each scavenging chamber has a radiation applicator that irradiates the interior of the scavenging chamber and creates a plasma therein from etchant gas flowing through the chamber from the etchant gas source to the gas distribution apparatus of the primary processing chamber. The applicator uses either an inductive discharge, capacitive discharge, direct current (DC) discharge or microwave discharge to irradiate the interior of the scavenging chamber and ignite the plasma. An etchant species scavenging source is also disposed within the scavenging chamber. This source provides scavenging material that interacts with the plasma to scavenge etchant species created by the dissociation of the etchant gas in the plasma and form etch by-products comprised of substances from both the etchant species and the scavenging source. The scavenging chambers can be employed, as is or in a modified form, as excitation chambers to excite gases at optimal conditions and feed the modified gases into the primary chamber. The scavenging chamber is modified by removing its scavenging source if this source would adversely interact with the gas being excited.