The Sns Cryogenic Control System: Experiences in Collaboration [1]

The cryogenic system for the Spallation Neutron Source (SNS) is designed by Jefferson Laboratory (JLab) personnel and is based on the existing JLab facility. Our task is to use the JLab control system design [2] as much as practical while remaining consistent with SNS control system standards. Some aspects of the systems are very similar, including equipment to be controlled, the need for PID loops and automatic sequences, and the use of EPICS. There are differences in device naming, system hardware, and software tools. The cryogenic system is the first SNS system to be developed using SNS standards. This paper reports on our experiences in integrating the new and the old. 1 PROJECT DESCRIPTION The SNS project is a partnership involving six DOE national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge. The project is described in more detail on the SNS website and elsewhere in these proceedings [3, 4]. The cryogenic system provides the refrigeration necessary to supply the 2.1° Kelvin liquid helium required for operation of the SNS accelerator superconducting cavities. Once the cryogenic refrigerator system is placed in service, it is expected to run continuously. Shutting down the cryogenic system is very expensive due to the loss of beam time and helium. Cryogenic refrigerator systems operate best with a fairly constant load. There are very few independent control loops; a change to any one control variable affects the entire system. The Cryogenic Control System (CCS) provides the coordinated control algorithms to support the complex operation of the cryogenic refrigeration system. 2 CONTROL SYSTEM OVERVIEW The top-level Integrated Control System (ICS) for the entire SNS project is based on the Experimental Physics and Industrial Control System (EPICS) suite of monitoring and control software. For the cryogenic systems, EPICS provides the operator interface for control and monitoring, alarming and archiving of selected signals, and routines to analyze real-time and historic data. All high level control algorithms, control loops and automatic sequences reside in EPICS. EPICS routines constantly monitor the state of the cryogenic system and update control outputs to keep the refrigerator system stable and the load constant. Programmable Logic Controllers (PLC) are used to interface signals from sensors and actuators to the EPICS Input/Output Controllers (IOC). PLCs perform low level interlocks, control loops and sequences. 3 DESIGN COLLABORATION JLab is designing and procuring the cryogenic plant and cryomodules including all mechanical equipment, instrumentation, and control devices. The control system at JLab uses EPICS. The SNS CCS duplicates the JLab system as much as practicable. The SNS Integrated Control System Group at the Oak Ridge National Laboratory (ORNL) is producing the CCS from the sensors and actuators up. This includes cables, signal conditioning, PLCs, VME based IOCs, boot servers, operator interface workstations, network hardware, and all control room equipment. Los Alamos National Laboratory (LANL) provides general EPICS support. LANL also provides the RF control system for the cryomodules and the RF signals needed by the CCS for use in heater control. Figure 1: Collaboration on the SNS Cryogenic System. Due to advances in hardware and software, there are differences in the CCS implementation between JLab and SNS. JLab has used their experience with an operating cryogenic system to provide invaluable 8th International Conference on Accelerator & Large Experimental Physics Control Systems, 2001, San Jose, California