Diagnostics and Control of the Time Evolution of Beam Parameters

Measurement tools for the betatron tunes, chromaticity and coupling exists in every circular accelerator. This article reviews diagnostic tools for the time evolution of these beam parameters in view of potential online feedbacks on magnetic elements in the LHC. For chromaticity measurements a new development made at CERN based on the detection of the phase difference between head and tail betatron oscillations is presented

Tune scans in LEP

Luminosity optimization in LEP required systematic studies of the dependence of some beam parameters on the values of the betatron tunes. For this purpose a measurement sequencer was conceived in the environment of the LEP control system which : a) changed the betatron tunes at a speed of about 0.5 Hz and b) acquired data from various beam instruments, such as transverse emittances, beam lifetimes and tunes, at a rate of about 2 Hz. This paper summarizes the experimental procedure and the subsequent data treatment. Results on the beam sizes as a function of the betatron tunes are shown

LHC technological challenges: use of digital signal processors in the power converters for the LHC particle accelerator

The Large Hadron Collider (LHC) is the next accelerator being constructed on the CERN site. It will be installed in a 27 km circumference tunnel, about 100 m underground. The LHC design is based on superconducting magnets (up to 9 T) which operate in a superfluid helium bath at 1.9 K. This machine is scheduled to come into operation in 2008. In all, there will be 1720 power converters having a total steady-state input power of 63 MW and a peak power of 86 MW. They will supply a total current of about 1850 kA and are, in general, characterized by having high current (up to 20 kA) and low voltage with very high precision. We describe the main components of the LHC powering and their challenges. The performance, design constraints, and topologies of the power converters will be presented. We discuss in detail the use of CERN-designed digital signal processor boards with the main emphasis being on the control loop design

Highlights from Beam Diagnostics

The quality of beam diagnostics is very important in accelerators for the optimization of machine performance and for the understanding of accelerator physics issues. Many examples of successful and outstanding beam instrumen-tation at different accelerators will be shown highlighting the following aspects: ultimate measurement resolution in space and time obtained exploiting different detection principles clever use of standard instrumentation tools benefit for beam instrumentation obtained from introducing digital signal treatment techniques

The measurement of Q' and Q'' in the CERN-SPS by head-tail phase shift analysis

A so-called "Head-Tail" chromaticity measurement system has recently been installed in the CERN-SPS, which allows the chromaticity (Q') to be calculated from several hundred turns of data after transverse excitation. The measurement relies on the periodic dephasing and rephasing that occurs between the head and tail of a single bunch for non-zero chromaticity. By measuring the turn-by-turn position data from two longitudinal positions in a bunch it is possible to extract the relative dephasing of the head and the tail, and so to determine the chromaticity. In addition, by changing the orbit of the circulating beam this technique allows the variation of chromaticity with radial position (Q'') to be measured with a much higher resolution than is currently possible using RF modulation. This paper describes this "Head-Tail" measurement technique and discusses some recent results obtained using prototype LHC beam (25ns spacing) in the CERN-SPS