Methods and apparatus are provided for igniting, modulating, and
sustaining a plasma for various plasma processes and treatments. Such
treatments include cleaning and sterilizing parts. In some embodiments, a
plasma is ignited by subjecting a gas in a multi-mode processing cavity
to electromagnetic radiation having a frequency between about 1 MHz and
about 333 GHz in the presence of a plasma catalyst. A part can be cleaned
by, for example, inserting hydrogen into the plasma and exposing the part
to the hydrogen-enriched plasma. A part can be sterilized by heating the
part with the plasma.