Dual branch high voltage pulse generator for the beam extraction of the Large Hadron Collider

The LHC beam extraction kicker system, MKD, is composed of 15 fast kicker magnets per beam to extract the particles in one turn from the collider and to dispose them, after dilution, on an external absorber. Each magnet is powered by a separate pulse generator. The original single branch generator consisted of a discharge capacitor in series with a solid state closing switch operating at 30 kV. In combination with a parallel freewheel diode stack this generator produced a current pulse of 2.7 μs rise time, 18.5 kA amplitude and about 1.8 ms fall time, of which only about 90 μs are needed to dump the beam. The freewheel diode circuit is equipiped with a flat top current droop compensation network, consisting of a low voltage, low stray inductance, high current discharge capacitor. Extensive reliability studies have meanwhile suggested to further increase the operational safety of this crucial system by equipping each generator with two parallel branches. This paper presents the re-designed dual branch generator and addresses technical difficulties, and approaches related to this design change, as well as further efforts intended to improve the overall reliability of the system. The final magnet current flat top compensation is also discussed, together with the low impedance transmission line between generator and magnet. This line consists of 8 parallel 18 Ohm coaxial power cables per magnet, each 19 m long, and is an important part of the circuit.