THE RELATIVISTIC HEAVY ION COLLIDER (RHIC) REFRIGERATOR SYSTEM AT BROOKHAVEN NATIONAL LABORATORY: SYSTEM PERFORMANCE AND OPERATIONS UPGRADES FOR 2003

The main function of the RHIC cryogenic system is to maintain the superconducting magnets in the two rings of the new collider-accelerator at Brookhaven National Laboratory at or below 4.5K. The main feature in the RHIC cryogenic system is the helium refrigerator. A new process control philosophy was implemented that allows this system to track the actual load from the accelerator rings and lets it respond accordingly. The refrigerator capacity decreases as the load decreases and increases as the load increases. This has resulted in the following improvements in the operation of the system: (1) Higher reliability because the rotating equipment does not have to run at full load continuously. (2) Greater stability because the system tracks the load continuously and responds quickly to any transients such as a quench. (3) Reduced power consumption because the discharge pressure of the system is adjusted continuously to match the load; therefore, the compressors draw less power when the load fi-om the accelerator rings decreases. This paper also addresses other modifications introduced that added to the efficiency, stability, and reliability of the system. As a result of this upgrade the Carnot efficiency of the refrigerator system has increased to 15% from around 10%