The SPS Beam Instrumentation and Closed Orbit Correction

For the running-in and the operation of a large accelerator like the SPS, the beam instrumentation plays a prominent part. Though limiting the beam detectors to where they are strictly necessary, their number is still considerable, leading to a large amount of data to be treated simultaneously. To do this efficiently, hardware and software are equally important and the design of the hardware had to be done jointly with the software. The type of detectors is determined by their function, intensity, position, profile, loss, etc... whereas the type of associated electronics and acquisition systems has to be restricted to a minimum for simplicity, production cost, easy maintenance and fast data treatment. Furthermore the small number of access shafts to the accelerator (6 for 7 km SPS ring circumference) and to the beam transfer lines leads to the transport of tiny signals over long distances (several hundred metres) in a noisy and irradiated environment. This paper summarizes the performance of the main types of detectors giving some particularities of their hardware and software with some emphasis on the closed orbit measurement and correction system.