Thermodynamic Booster for the CERN Omega Cryoplant

Publisher Summary This chapter provides a brief description of the OMEGA refrigeration cycle. It analyzes the problems encountered and explains the technical approach of "thermodynamic boosting". It presents the flow scheme of the cycles. The 800 W at 4.5 K cryoplant, commissioned in 1971 for the superconducting magnet of the OMEGA particle detector, uses a large reciprocating compressor designed for the delivery of helium at a rate of 216 g/s at 20 bar. A recurrent problem, which overshadowed the good performance of the plant, is the rapid wear of the labyrinth-type, compressor piston seals. This is due to the high temperature of the compressed gas, a consequence of the rather high compression ratio per stage. A costly replacement of the compressor, by a better suited modern machine, is foreseen. Eventually, however, the problem is solved in a much cheaper way by inserting an auxiliary cooling stage between the compressor and the cold box. This is done with a commercial, fully automated, R22 refrigerator which reduced the helium temperature, at compressor suction and delivery, from ambient to about 10°C. The result is not only an increase in cooling power of nearly 10%, but also a reduction in the labyrinth wear to a level hardly expected.