Microwave Oven Plasma Reactor Moding and Its Detection

Abstract

Over the last 20 years microwave power supplies in domestic microwave ovens have increasingly found applications in plasma reactors for processing of functional carbon-based nanostructures for engineering materials, electronics and biomedical applications. However, the packaged magnetrons used in the microwave ovens are known to suffer from moding due to frequency pushing and pulling, both of which may limit the efficiency of the plasma treatment process. This paper explores patent records for high voltage doubler circuits, coupled to the cathode filament heater circuit as the magnetron pushing source and the multimode resonant cavity plasma load as the pulling source. These circuits are compared with microwave oven plasma reactor circuits published in peer reviewed journals. This study highlights that a number of academic research groups have investigated power supply design parameters such as the input transformer voltage, as well as the power level using different capacitors values, as a result the transformer output is poorly described. Identification of moding within the plasma reactors due to magnetron warm-up time and changing cavity load conditions is also poorly reported. This work attempts to address this information gap on microwave oven plasma processes, through the extraction of reports on a packaged magnetron warm-up times and near-field E-probe mode measurement within the Cambridge Fluid Systems MRC 200 plasma reactor using a argon and hydrogen plasma.