A toroidal, inductively coupled plasma processing apparatus, the apparatus comprising: a vessel (510a, 510b, 510c, 510d; 610; 1210; 1510) defining an enclosed channel, wherein the channel defines a toroidal shape; at least one heat sink segment (630;1220) adjacent to the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510) and having a dimension aligned with an adjacent portion of the channel, a total length of the dimension of the at least one heat sink segment being greater than 10% of a length of the channel, a thermal interface disposed between the vessel and the heat sink segment, wherein the thermal interface defines a space between the heat sink and the vessel that accommodates a movement of at least one of the thermal interface, the heat sink, and the vessel in response to thermally induced dimensional changes; wherein the at least one heat sink segment serves as a capacitively coupled ignition electrode to apply an electric field to a gas in the channel to initiate plasma discharge of the gas, and a reference electrode adjacent to the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510), wherein the at least one heat sink segment and the reference electrode cooperate to apply an electric field to the gas in the channel to initiate plasma discharge of the gas, the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510) having at least four surfaces at least partly covered by the heat sink segment and the reference electrode; characterized by the reference electrode covering at least a portion of each of three of the at least four surfaces, and the heat sink segment (630; 1220) covering at least a portion of a remaining surface of the four surfaces of the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510). a vessel (510a, 510b, 510c, 510d; 610; 1210; 1510) defining an enclosed channel, wherein the channel defines a toroidal shape; at least one heat sink segment (630;1220) adjacent to the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510) and having a dimension aligned with an adjacent portion of the channel, a total length of the dimension of the at least one heat sink segment being greater than 10% of a length of the channel, a thermal interface disposed between the vessel and the heat sink segment, wherein the thermal interface defines a space between the heat sink and the vessel that accommodates a movement of at least one of the thermal interface, the heat sink, and the vessel in response to thermally induced dimensional changes; wherein the at least one heat sink segment serves as a capacitively coupled ignition electrode to apply an electric field to a gas in the channel to initiate plasma discharge of the gas, and a reference electrode adjacent to the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510), wherein the at least one heat sink segment and the reference electrode cooperate to apply an electric field to the gas in the channel to initiate plasma discharge of the gas, the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510) having at least four surfaces at least partly covered by the heat sink segment and the reference electrode; characterized by the reference electrode covering at least a portion of each of three of the at least four surfaces, and the heat sink segment (630; 1220) covering at least a portion of a remaining surface of the four surfaces of the vessel (510a, 510b, 510c, 510d; 610; 1210; 1510).