Cryogenic Systems

In this lecture we discuss the principle of method of cooling to a very low temperature, i.e. cryogenic. The "gas molecular model" will be introduced to explain the mechanism cooling by the expansion engine and the Joule-Thomson expansion valve. These two expansion processes are normally used in helium refrigeration systems to cool the process gas to cryogenic temperature. The reverse Carnot cycle will be discussed in detail as an ideal refrigeration cycle. First the fundamental process of liquefaction and refrigeration cycles will be discussed, and then the practical helium refrigeration system. The process flow of the system and the key components; -compressor, expander, and heat exchanger- will be discussed. As an example of an actual refrigeration system, we will use the cryogenic system for the KEKB superconducting RF cavity. We will also discuss the liquid helium distribution system, which is very important, especially for the cryogenic systems used in accelerator applications.

1 Principles of Cooling and Fundamental Cooling Cycle

2 Expansion engine, Joule-Thomson expansion, kinetic molecular theory, and enthalpy

3 Liquefaction Systems

4 Refrigeration Systems

5 Practical helium liquefier/refrigeration system

6 Cryogenic System for TRISTAN Superconducting RF Cavity