Patent ID: 7437878

Claim:
An improved, pulse tube cryocooler having cascaded, multiple stages in which each stage includes a cold head comprising a regenerator connected to one end of a pulse tube and an acoustic impedance connected to the cold head at the opposite end of the pulse tube in order to properly phase the internal gas pressure and velocity, each cold head having a cold region for accepting heat and a warm region for rejecting heat, the cold heads being staged by thermally connecting the cold region of a lower stage to the warm region of a higher stage, wherein the improvement comprises: at least a portion of the acoustic impedance of a selected stage, higher than the first stage, spaced outwardly from and surrounding the cold head of the selected stage; wherein the acoustic impedance is formed of a metal having a thermal diffusivity of at least 20E-06 m 2 /s; wherein the acoustic impedance of the selected stage is mounted in thermally conductive connection to the warm region of the selected stage for cooling the acoustic impedance; wherein the selected stage is a U-tube configuration; wherein the acoustic impedance is annular; and wherein the acoustic impedance comprises an annular reservoir and an inertance tube wound around within the reservoir.