Microwave excitation of submerged plasma bubbles

Steady-state models were formulated for spherical plasma bubbles, excited in water by an external microwave radiation source. The bubbles were assumed to be at rest relative to the surrounding water, and the energy absorbed by the plasma was balanced by energy loss through thermal conductance and convection to the surrounding water. Two regimes were considered: (1) bubbles with radii R less than the skin depth δ, i.e. R<δ, and (2) bubbles with R>δ. A self-consistent system of equations was formulated. In the R<δ case, a considerable difference was found between electron temperature and the temperature of the heavy plasma components, but this difference decreased with increasing radius. The calculations showed that the bubble radius decreased with increasing electric field amplitude, but R in the R>δ case obtained for strong electric fields was larger than in the R<δ weak field case. The R>δ bubbles had an isothermal core and power from the microwave field was absorbed in a relatively thin layer in the plasma bubble.