Operation Modes of the Fast 60 kV Resonant Charging Power Supply for the LHC Inflectors

CERN, the European Laboratory for Particle Physics, is constructing a Large Hadron Collider (LHC) to be installed in the existing LEP tunnel of 27 km circumference. The LHC will accelerate two proton beams, injected at 450 GeV, in opposite directions and will collide them at a centre of mass energy of 14 TeV. The injection kicker systems will consist of four travelling wave type magnets and four pulse forming networks (PFN's) for each beam, discharged by thyratron switches. Resonant Charging Systems (RCS), located with the switches and PFN's in a gallery parallel to the LHC tunnel, are employed to charge the PFN's within 1 ms to 60 kV. The aim of this fast charging is to minimise the number of spontaneous firings of the thyratron.The stability and pulse to pulse reproducibility of the charging voltage must be maintained to a precision of ± 0.1%. Each resonant charging system consists of a 2.4 mF primary capacitor bank, charged to 2.5 kV, and connected via a Gate Turn-Off thyristor (GTO) and a 1:23 step-up transformer to two PFN's of 5 Ohms characteristic impedance, each with a total capacitance of 0.96 µF. The PFN's are discharged 400 µs after the end of the charging period into the kicker magnets. The GTO switch is used in Gate Assisted Turn-off (GAT) mode and the pulse transformer has a particularly low leakage inductance. In this paper special attention is paid to analogue circuit simulations of the RCS showing both normal and abnormal operating modes. Furthermore the choice of electrical components is presented and discussed. These RCS's are designed, constructed and tested at TRIUMF in collaboration with CERN as part of the Canadian contribution to the LHC project.