A Kicker Pulse Generator for Measurement of the Tune and Dynamic Aperture in the LHC

Abstract

The large hadron collider (LHC) at CERN will be equipped with fast pulsed two-function magnets, which will be part of the measurement system for the tune and the dynamic aperture. For the tune measurement, the magnets will excite coherent oscillations of part of the beam. This is achieved by means of a generator producing a 5.1 mus base half-sine pulse of 1.2 kA amplitude, superimposed with a 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic to produce a -2 mus flat top. A kick repetition rate of 2 Hz is possible. The maximum generator voltage is 3.3 kV, with a dynamic range of about 20. A 5.2 kV press-pack capsule IGBT is used as switching element. A fast 30 A gate driver is used for triggering. The generator pulse current interruption is obtained with an extra-fast small recovery series diode. Several advantages of the press-pack IGBT construction with respect to conventional IGBT modules will be discussed. To measure the dynamic aperture of the LHC at different beam energies, the same magnets will also be driven by a more powerful generator which produces a 43 mus base half-sine current pulse of 3.8 kA. The maximum generator voltage is 890 V and the dynamic range of this system is about 10. A fast 2.5 kV thyristor is used as switching element. For reliability reasons, self-healing type capacitors are employed in both generators. Various interlocks have been introduced in the circuits to assure a safe functioning. A prototype pulse generator has been successfully tested both in the Q-measurement and in the dynamic aperture measurement modes. Measurements are satisfactory compared to PSpice previous simulation calculations