What Are the Controls Requirements for the Global Accelerator Network?

The Global Accelerator Network is a proposed model for remote operation of a future large accelerator by the partners of an international collaboration. The remote functionality would include not only routine operation and machine studies, but also hardware diagnostic tests and software maintenance and development, so the control system must offer both high and low level remote access to the accelerator and its components. We discuss in this paper some of the special requirements, and how they might be satisfied using current or developing technology, such as web-based applications and industrial automation standards. The choices made must be acceptable to the collaboration, but will also have a strong influence on its effectiveness. The biggest technical challenge is likely to be the middle layer software which is responsible for system integration, automation, and presentation of the machine state to the operating staff.