Recent Operating Experience with the Fermilab Central Helium Liquefier

Operating experience since the last report, Aug. 1983, is covered. The current mode of supplying liquid helium to the superconducting accelerator ring is explained including a discussion of the interaction of the system with upsets in the ring. The method of controlling helium flow to the dewars, liquid helium pump, helium subcooler, and cold box is very stable and largely automatic. The capacity of the plant is 136 g/s at the current operating point with a peak demand flow of greater than 250 g/s using liquid pumped from dewar storage. The design specifications of the major equipment are tabulated giving the main characteristics of the compressors, cold box, and helium and nitrogen storage. The operating history is analyzed to yield a lifetime efficiency of 97% in 19840 hours of running, and a breakdown of major failures and their causes is given. The major sources of downtime have been contamination of the helium stream by dust, water, and nitrogen. The solutions to these problems are discussed. A new liquid helium pump has been commissioned which has improved the system reliability and performance. This reciprocating pump is described and test data is presented. A third compressor has been commissioned as a backup for the two original compressors. A new control system utilizing a Texas Instruments PM550 programmable controller is used to monitor and control the third compressor. The performance of the PM550 has been excellent, and it is being implemented to control other parts of the system.