Instrumentation and diagnostics used in LEP commissioning, with accent on the LEP beam orbit measurement system

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Abstract
The LEP machine is equipped with a very complete instrumentation [1,2] for beam position intensity and profile, tune and optic parameters, interaction rate, from which a summary is first presented. Second, the largest instrument for beam orbit measurement is described in more depgh. The Beam Orbit Measurement (BOM) System with its 504 Beam Position Monitors and 40 Processing Electronics Racks distributed along the 27 km of the LEP tunnel and linked by the Control System’s Token Ring has been installed and pre‐tested with simulated beam signals. The signal processing equipment must guarantee high reliability and precision despite high γ‐irradiation and long cable transmission. In addition most of the electronics will not be accessible during operation. The analog signal processing is based on normalizers using phase modulation and on Flash ADC’s. Local memories allow the recording of data at each bunch passage for more than 1000 revolutions. It is followed by digital signal processing in local VME crates equipped with MC68000 microprocessor. The BOM system will be able to acquire data of up to bunches from which injection trajectories, average orbits, integer and fractional part of Q, β function and post event analysis will be processed. A first test with beam was successfully performed on a single station equipped for 12 monitors during the injection test of July 1988. It did validate the hardware and processing design. But complete results could only be reached in July 1989 when the proper triggering of all electronic stations could be adjusted on the circulating beam, via the Beam Synchronous Timing System. Most of the data analysis is done simultaneously in 40 microprocessors which communicate with a data Collector. Operational results are presented. The BOM System has been a key instrument for the success of LEP performance.

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