Abstract: A two-stage pulse tube cryocooler, having compact size, less vibration and lower manufacturing cost is disclosed, in which at least a first stage of the cryocooler is coaxial, but in which first and second stages may be coaxial by locating circular regenerators of each stage inside of corresponding annular pulse tubes. A second stage circular regenerator is installed below a first stage regenerator. This configuration allows preassembly of the regenerator assembly and a base tube assembly in one or more stages. The pulse tube, which is annular, is coaxially formed with an outside surface of the assembled regenerator assembly and an inner surface of the outer tube of the base tube assembly after installation of the regenerator assembly.