Simulation Using Xorbit with EPICS

The accelerator code Xorbit has an interface to the Experimental Physics and Industrial Control System (EPICS). This means that machine data such as magnet settings can be sent to Xorbit via EPICS, and the resulting orbit parameters such as beta functions, etc., can be calculated. In addition, Xorbit can be made to simulate the real machine, whether the latter is running or not. To accomplish this for the APS, there is a database of process variables in an IOC corresponding to each APS ring and beamline. These process variables are very similar to the real process variables that read and set power supplies and read monitors, except that when a setting is changed, Xorbit is notified via a callback, calculates a new orbit, and outputs the appropriate readbacks to the database. By attaching the string ``Xorbit:`` to a control name the control system will respond to the simulation rather than the real system. This allows the testing of control algorithms, orbit diagnostics, and many other components of the control system (as well as EPICS itself). It is fast enough to be visually similar to accessing the real system.