A refrigeration system includes a compressor. In the method, a plurality of data packets from the data stream are analyzed in order to generate profile data which indicates how one or more parts of each of the plurality of data packets varies from data packet to data packet. A second type dopant is doped into at least one of the second barrier layers, and a concentration of the second dopant in the second barrier layer is higher than that of the second dopant in the second type nitride semiconductor layer. The superconducting preforms are moved from the carrier onto the drawn carbon nanotube film by applying an electric field between the drawn carbon nanotube film and the carrier.