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Because acoustic power density is proportional to frequency, the size of pulse tube cryocoolers for a given
refrigeration power can be reduced by operating them at higher frequencies. A frequency of about 60 Hz had been
considered the maximum frequency that could be used while maintaining high efficiency. Recently, we have shown
through modeling that by decreasing the volume and hydraulic diameter of the regenerator and increasing the average
pressure, it is possible to maintain high efficiency even for frequencies of several hundred hertz. Subsequent
experimental results have demonstrated high efficiencies for frequencies of 100 to 140 Hz. The very high power density
achieved at higher pressures and higher frequencies leads to very short cooldown times and very compact devices. The
use of even higher frequencies requires the development of special compressors designed for such conditions and the
development of regenerator matrices with hydraulic diameters less than about 30 Μm. To demonstrate the advantages of
higher frequency operation, we discuss here the development of a miniature pulse tube cryocooler designed to operate at
80 K with a frequency of 150 Hz and an average pressure of 5.0 MPa. The regenerator diameter and length are 4.4 mm
and 27 mm, respectively. The lowest temperature achieved to date has been 97 K, but a net refrigeration power of 530
mW was achieved at 120 K. Acoustic mismatches with existing compressors significantly limit the efficiency, but
necessary modifications to improve the acoustic impedance match between the compressor and the cold head are
discussed briefly.
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