BaBar helium liquefier and superconducting magnet control system

The BaBar 27 MJ superconducting solenoid and 1000 W helium liquefier at the Stanford Linear Accelerator Center (SLAC) have been operating with high reliability since October 1998. The control system consists of two Allen Bradley SLC 500/4 PLC controllers and two Windows NT PCs running BridgeView as the Graphical User Interface (GUI) all connected via a common Data Highway Plus network. A third 500/4 PLC and PC have been recently added to the network, integrating control of a second compressor system that is used with another helium liquefier. Separate hardwired protection systems for both the solenoid and liquefier are provided. All GUI screens are viewable over the Web. Operating, upgrading and commissioning experience of this control system is discussed. Control system hardware, software technical performance, and instrumentation and wiring issues are detailed. Operator interaction issues are also included.