Disclosed is an apparatus and a method for fumigation using chlorine dioxide. The packet generator 28A causes the switch 21A to perform ONOFF operation, based on a target voltage, and a voltage estimated as being applied to a load 4A in each of a state where a power packet is supplied to the load and a state where no power packet is supplied to the load. The power transfer system has at least two electrical elements, e. The systems and methods emit radiation at a selected wavelength into the plasma to activate the photoactive material and thereby eradicate the contaminant that is free of entrainment by cellular matter.