Managing the real-time behaviour of a particle beam factory: the CERN Proton Synchrotron complex and its timing system principles

In the CERN 26 GeV Proton Synchrotron (PS) accelerator network, super-cycles are defined as sequences of different kinds of beams produced repetitively. Each of these beams is characterised by attributes such as particle type, beam energy, its route through the accelerator network, and the final end user. The super-cycle is programmed by means of an editor through which the operational requirements of the physics programme can be described. Each beam in the normal sequence may later be replaced by a set of spare beams automatically depending on software and hardware interlocks and requests presented to the Master Timing Generator. The MTG calculates at run time how each beam is to be manufactured, and sends a telegram message to each accelerator, just before each cycle, describing what it should be doing now and during the next cycle. These messages, together with key machine timing events and clocks are encoded onto a timing distribution drop net where they are distributed around the PS complex to VME-standard timing reception TG8 modules which generate output pulses and VME bus interrupts for task synchronisation. The TG8 modules are able to use accelerator-related clocks such as the incremental/decremental magnetic field trains, or the beam revolution and radio frequencies to produce high precision beam synchronous timing. Timing Surveillance Modules (TSM) monitor these timings, which give high precision interval measurements used for the machine tuning, beam diagnostics, and fault detection systems.