Model - Based Expert Systems for Linac Computer Controls

The use of machine modeling and beam simulation programs for the control of accelerator operation has become standard practice. The success of a model-based control operation depends on how the parameter to be controlled is measured, how the measured data is analyzed, how the result of the analysis is interpreted, and how a solution is implemented. There is considerable interest in applying expert systems technology that can automate all of these processes. The design of an expert system to control the beam trajectory in linear accelerators will be -discussed as an illustration of this approach. MODEL-BASED CONTROL PROGRAMS The design of linear accelerators requires the use of computer programs in a variety of roles. At the most basic level, the designers use these programs to est.imate the effects of various beamline configurations on observable beam parameters of interest with the goal of finding an “ideal” configuration that yields beam parameters meeting specific design requirements. At another level, the designers use the programs to compute the effects of configuration errors on the observable beam parameters and to find correction schemes that compensate such effects. At the highest level, these programs, used as components of the monitoring and control systems, allow the beamline operator to efficiently achieve and maintain proper machine operation. The primary function of the modeling programs is to compute a number of machine functions and beam properties at various positions for given beamline configurations. Here, “configuration” is defined as the location and parameter values for each beamline element. In general, the beam properties are computed from the machine functions. As an example, the beam trajectory is a typical beam property that is computed from the machine function called the Transport Matrix which specifies the relationship between the beam coordinates at one point with those at another. For linear accelerators the beam properties also depend on the launch conditions, the beam parameter values at the entrance of the beam line. Typical launch parameters are the beam coordinates and momenta at the beginning