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Tune, chromaticity and orbit of the LHC beams have to be precisely controlled by synchronising the magnetic field of quadrupole, sextupole and corrector magnets.This is a challenging task for an accelerator using superconducting magnets, whose field and field errors will have large dynamic effects.The accelerator physics requirements are tight due to the limited dynamic aperture and the large energy stored in the beams.The power converters need to be programmed in order to generate the magnetic functions with defined tolerances. During the injection process and the energy ramp the magnetic performance cannot be predicted with sufficient accuracy, and therefore real-time feedback systems based on magnetic measurements and beam observations are proposed. Beam measurements are used to determine a correction factor for some of the power converters. From magnetic measurements the excitation of small magnets to compensate the sextupolar (b 3 ) and decapolar (b 5 ) field components in the dipole magnets will be derived. To meet these requirements a deterministic control system is envisaged.

The field quality of the main magnets in the LHC will be, in part, dependent upon the shape of the magnetic field as a function of time. A theoretical optimisation of this function has been carried-out with the aim of minimising the dynamic errors [3]. This work resulted in the definition of a current ramp function composed of mathematically defined, smoothly joining segments. A prototype digital controller based on a DSP has been developed and built [4]. In this equipment the current ramp is computed from the segment equations in real time. The user need only supply the characteristic parameters for the segments in order to define the ramp. In this paper, the effect of the ramp function on the error terms is discussed and the corresponding segment equations are given.The prototype implementation is described and actual results are shown.

SummaryThe CERN PS Booster (PSB) has been connected to the new computer control system (NORD-CAMAC) during the four months' shutdown in summer and autumn 1980. Subsequently the PSB had to furnish beams of high quality, particularly for the Antiproton Accumulator (AA). To make the change-over efficient and possible within the time and manpower limitations, local autonomous microcomputer-aided test facilities were used for more than a year.These were designed (i) for the development of process equipment including its electronics, (ii) for equipment commissioning, (iii) for fault diagnosis and (iv) for the improvement of the future machine performances.The specifications, the detailed implementation and the results are reported.

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