A.D.Cox
Beam Line 9, currently under construction with XAS and crystallography stations for structural molecular biology, will break new ground in its control system.
Instead of the VAX/VMS + CAMAC arrangement which is currently the `norm' at SSRL, Beam Line 9 will use Unix workstations and VME-based data acquisition and control hardware. The basis for the control system is a software package called EPICS, an acronym for Experimental Physics and Industrial Control System. EPICS was developed originally at Los Alamos and Argonne national laboratories, but has recently been adopted and extended by several other DOE laboratories and a number of other educational institutions. The Advanced Photon Source has adopted EPICS for both synchrotron control and beam line data acquisition, as have most of the APS CATS (Collaborative Access Team). SSRL is contributing to the continuing software development effort by implementing EPICS on the 64-bit Alpha/Unix platform.
In an EPICS system, the `real-time' aspects of data collection are performed in a VME-based computer system running a small, dedicated, real-time operating system. The hardware; motors, scalers and timers are directly attached to the VME backplane.
Since this computer system is dedicated exclusively to the data collection and control, it is possible to implement reliable `stand-alone' algorithms to implement such features as adaptive optic control and beam line monitoring as well as running experiments.
The other half of an EPICS system is the Unix workstation. This computer system provides not only `boot-time' services for the VME-based computers, but also runs programs to alignment, testing, logging, and eventually, experimental data collection. The workstation and the real-time processors are connected over the network.
We aim to integrate existing programs running on VMS/ALPHA systems, with the EPICS system, but the long-term aim is to implement new program code, sharing developments with other synchrotron laboratories. Implementation of a common software framework (EPICS) will allow us to improve productivity and eventually to provide a common interface (or a number of common interfaces) over many different synchrotron laboratories. Experience with the implementation of Beam Line 9 will show us if this approach can be successfully extended to other beam lines at SSRL.