E. Carlier

Solid state switch application for the LHC extraction kicker pulse generator

A semiconductor solid state switch has been constructed and tested in the prototype extraction kicker pulse generator of CERNs Large Hadron Collider (LHC). The switch is made of 10 modified 4.5 kV, 66 mm symmetric GTOs (also called FHCT-fast high current thyristor), connected in series. It holds off a DC voltage of 30 kV and conducts a 5 /spl mu/s half-sine wave current of 20 kA with an initial di/dt of 10 kA//spl mu/s. Major advantages of the switch are the extremely low self-firing hazard, no power consumption during the ready-to-go status, instantaneous availability, simple condition control, very low noise emission during soft turn-on switching and easy maintenance. However, the inherent soft, relatively slow turn-on time is a nonnegligible part of the required rise time and this involves adaptation of generator components. A dynamic current range of 16 is achieved with variations in rise time, which stay within acceptable limits. Important generator improvements have been made with the series diodes and freewheel diodes. A more efficient droop compensation circuit is being studied. It is directly connected in series with the freewheel diode stack and maintains an acceptable flattop variation of 5% of the magnet current during 90 /spl mu/s. This paper presents the complete generator, in particular the solid state switch, and discusses related electrical measurements.

Construction and 60 kV tests of the prototype pulser for the LHC injection kicker system

The European Laboratory for Particle Physics (CERN) is constructing the Large Hadron Collider (LHC). Two counter-rotating proton beams will be injected into the LHC at an energy of 450 GeV by two kicker magnet systems, producing magnetic field pulses of approximately 900 ns rise time and 6.6 /spl mu/s flat top duration with a ripple of less than /spl plusmn/0.5%. Both injection systems are composed of 4 travelling wave kicker magnets of 2.17 m length each, powered by pulse forming networks (PFNs). To achieve the high-required kick strength of 1.2 Tm, for a compact and cost efficient design, a characteristic impedance of 5 Ohms has been chosen. The design strategy for the magnets and generators has been defined after detailed analysis of existing systems. The electrical circuit has been optimised using the circuit analysis software PSpice. Most known parasitics have been modelled. A prototype PFN has been constructed at CERN and successfully tested at 60 kV. A calibration procedure has been developed and utilised for obtaining correction data for a high voltage probe and oscilloscope amplifier. Measurements carried out with a precision of approximately /spl plusmn/0.1% show that the prototype PFN conforms to the specifications and the PSpice predictions.

Design aspects related to the reliability of the LHC beam dump kicker systems

The two LHC beam dump kicker systems consist each of 14 pulse generator and magnet subsystems. Their task is to extract on request the beams in synchronisation with the gap in the beam. This operation must be fail-safe to avoid disastrous consequences due to loss of the beam inside the LHC. Only a failing operation of one of the 14 pulse generators is allowed. To preserve this tolerance premature beam dumps are forced immediately after early detection of internal faults. However, these faults should occur rarely in order not to be a source of undesirable downtime of the LHC. The report determines first the level of reliability required for the main components of the system. In particular faults which could cause spontaneously non-synchronised beam identified. Then, technical solutions are evaluated on failure behaviour. Those having a most likely failure mode which does not cause dump triggers are favoured. These solutions need redundancy and are more complex but have the advantage to be fault tolerant. The design goal can be achieved with a combination of high quality components, redundant signal paths, fault tolerant subsystems, continuous surveillance and check-list validation tests before the start of the injection of beam in the LHC.

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

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 3rd 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

Operation modes of the fast 60 kV resonant charging power supply for the LHC inflectors

CERN 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 (PFNs) for each beam, discharged by thyratron switches. Resonant charging systems (RCS), located with the switches and PFNs in a gallery parallel to the LHC tunnel, are employed to charge the PFNs 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 /spl les/+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 PFNs of 5 /spl Omega/ characteristic impedance, each with a total capacitance of 0.96 /spl mu/F. The PFNs are discharged 400 /spl mu/s 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 RCSs are designed, constructed and tested at TRIUMF in collaboration with CERN as part of the Canadian contribution to the LHC project.

A high power pulse generator for the beam dumping kicker system of cern's large electron positron co

CERN is upgrading its 55 GeV Large Electron Positron storage ring (LEP) to an energy of up to 100 GeV per beam and to higher intensities. Adequate equipment for rapid dumping of the counter-rotating beam bunches at the end of the storage period or in an emergency situation is therefore required. A fast kicker magnet system has been built for this purpose. The magnet is energized by the discharge of a storage capacitor, located close to the magnet in the LEP tunnel. The charging voltage of the capacitor is proportional to the beam momentum which is 20 GeV/c at injection and will be I00 GeV/c at top energy. The current pulse has a rnaxiinum amplitude of 9.S kA with a rise time of 9.2 ps and a fall time constant of 285 ps. The generator consists of a pulse capacitor discharged by a gas switch in series with a stack of blocking diodes, specially selected for very low reverse recovery energy. A free-wheel diode stack, in series with a small series resistor for slope control, bypasses the generator output. These free-wheel diodes have a very low dynamic forward resistance. After a short presentation of the layout of the dumping system and its kicker magnet this paper discusses in more detail the pulse generator with emphasis on the performances of the fast diode stacks. Results of measurements on the operational generator at design voltage will also be discussed.