This paper reviews the recent progress of the small cryocoolers operating near 4K, for the application of small scale superconducting magnets or superconducting devices.
The research and development scheme of cryocoolers can be classified into two categories. The first one is related to the investigation of reliability, compactness and cutting costs of the well known cryocooler systems. Stirling or G-M cycle cryocoolers with a J-T loop and small scale claude cycle also belong in this category. The second one is a fundamental approach to the novel refrigeration systems such as a magnetic refrigerator or regenerative cryocoolers which can be cooled down to liquid Helium temperature without J-T loop. A cascade J-T system using gas adsorption compressor is also included.
