Pressure Wave Systems has demonstrated the 4K operation of a Sumitomo RDK-101 GM cold head and the Pressure Wave Systems PWG500 bellows compressor with an electrical input power of 550W reaching 30mW @ 4.2K. This result opens up a new window of operation for many applications needing  only limited cooling power at low temperature. The very low energy consumption also results in an excellent noise performance of the compressor. Ask for a demo at your site!