CERN, the European Organization for NuclearResearch, is close to starting operation of the Large Hadron Collider (LHC). A beam dumping system must protect the LHC machine from damage, by reliably and safely extracting and absorbing the circulating beams when requested. For this purpose a beam extraction system has been designed, built, installed and tested. It is composed of 15 fast kicker magnets per beam line to extract the particles in one turn of the collider. Each magnet is powered by a dedicated pulse generator through special low impedance coaxial cables. The generator charging voltage is proportional to the beam momentum, which is 450 GeV/c at injection and will be 7 TeV/c at top energy. The current pulse has a maximum amplitude of 19 kA with a rise time of 2.8 μs and a fall time of 2 ms; the first 89 μs of the fall time are used to dump the beam. Each kicker magnet consists of a window frame of Si-Fe tape wound cores and high voltage insulated single turn conductors. They are built around a ceramic vacuum chamber which is metallized on the inside. The measures taken to ensure a high reliability of the system, which was one of the main considerations during the design, construction and testing of the system, are discussed. Results of measurements on the series systems are presented.
Abstract-Fast-pulsed magnets, also called kickers, are used in particle accelerators for beam injection, extraction and similar applications. To excite these magnets, typically current pulses with rise and fall times in the range of 100 ns to 10 s are used, with a pulse duration of up to 100 s and amplitudes in the order of kilo amperes. The short rise time imposes low-inductance circuits and high-voltage operation. The yokes are usually made out of ferrite, with field saturation being reached at about 0.5 T. To remove the 7-TeV proton beams safely from the large hadron collider (LHC), 15 beam-dump kickers are used for each of the two rings which must provide an overall bending strength of 6.2 T m with a rise time of about 3 s and a flat top duration of 90 s. For the first time steel with saturation above 1.5 T has been used as yoke material for such a short rise time. Due to eddy current losses the yokes must be laminated. The lamination thickness of 50 m is determined by the frequency spectrum of the current pulse and by the steel quality. The insulation layer of the laminations shall withstand a voltage of 1 V/layer, which is difficult to achieve at the cut edges. As stamping, handling and assembly of 1.2-m-long magnets with such thin sheets would be extremely difficult, the concept of tape-wound C-shaped cut cores was developed. Two cores are moulded together in charged epoxy resin with a thin intermediate insulator. The yoke is finally assembled from a series of such "twin packs," using threaded inserts for precision mounting. This paper discusses the choice of the steel quality and lamination thickness, and addresses technical challenges related to the manufacturing of the C-cores, arising from the tight mechanical, electrical and magnetic requirements.
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