The Clinical Neutron Therapy System (CNTS) at the University of Washington is a computer controlled cyclotron and neutron therapy treatment facility. It provides particle beams for cancer treatments with fast neutrons, production of medical isotopes, and experiments in medical physics and radiobiology. Its control system includes six processors and handles over one thousand input and output signals. It must meet demanding requirements for availability, equipment protection, and human safety. Devices under computer control include a 900 amp electromagnet and a 39 ton rotating gantry.

This document is the introduction to the functional specification of the CNTS control system. It is intended for an audience including physicists, engineers, computer science researchers and computer programmers. It contains much material describing the the cyclotron and treatment apparatus and explaining how the whole system works. This is necessary to enable the specification to be understood by readers with diverse backgrounds. It is also necessary to explain the rationale for many features, particularly those concerned with safety and equipment protection.

We created an informal specification. We describe the control system as thoroughly as is practical using standard technical English, supplemented by tables and diagrams. The only mathematical, or formal, contents are some algebraic equations and a few Petri net diagrams (which are explained prior to their use).

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