  Here we report the performance of a small scale 4 K pulse tube cryocooler
operating with a low input power reaching a minimum temperature of 2.2 K, as
well as a cooling capacity of over 240 mW at 4.2 K. The compressor is air
cooled and can be supplied by single phase power sockets. With an input power
of about 1.3 kW the coefficient of performance reaches values of up to 185
mW/kW, which is among the highest currently reported values for small to medium
power pulse tubes. The combination of an oil-free Helium compressor and low
maintenance pulse tube cryocooler provides a unique miniaturized, energy
efficient and mobile cooling tool for applications at 4 K and below.
