An energy coupling device for coupling energy into molten metal. The energy coupling device includes a cavitation source which supplies energy through a cooling medium and through a receptor in contact with the molten metal. The cavitation source includes a probe disposed in a cooling channel. The probe has at least one injection port for injection of a cooling medium between a bottom of the probe and the receptor. The probe under operation produces cavitations in the cooling medium. The cavitations are directed through the cooling medium to the receptor.