Digital cryogenic control system for superconducting RF cavities in CESR

Effective cryomodule control and monitoring are essential components to successful operation of CESR (Cornell Electron Storage Ring). The ability to quickly diagnose system problems can have a dramatic effect on machine down time. The CESR SRF Digital Cryomodule control system, employing a PC and a commercial PLC and user interface, is presented. With these tools, system status is available at a glance or, if needed, detailed system information can be displayed. Straightforward configuration of PID (Proportional Integral Derivative) control loops, safety interlocks, signal display, and data acquisition is the main feature of the system. The SRF cryomodules have several modes of operation. For example, under normal machine running conditions, liquid helium level is regulated using a liquid-level signal as the process variable (PV). For cryostat cool-down, the flow rate of cold helium gas returning to the refrigerator directly reflects cryomodule cooling rate and is a more useful process variable. Both these operational modes use the same control variable (CV): the liquid helium supply valve control signal. Other operational modes include warm-up and RF processing. This control system can be reconfigured quickly to meet the conditions of different operational modes.