Experimental and numerical studies of microwave power redistribution during thermal runaway

Plasma-assisted heating of Al2O3 is used to study power redistribution during thermal runaway when two samples are simultaneously heated in a microwave cavity. It is observed that thermal runaway in one of the samples completely suppresses the power availability to the other, demonstrating that thermal runaway in one region of the cavity acts as a “sink” for microwave power. Similar effects were observed during localized thermal runaway in a spatially extended single sample. Experimental trends were explored numerically by calculating the temperature evolution T (t) when one of the samples undergoes thermal runaway. Numerical investigation qualitatively captures the essential feature that thermal instability in one sample rapidly decreases the temperature of the second sample in agreement with the experimental observation. Experimental and numerical results as well as practical implications are discussed in the context of microwave processing of materials.