Eugène B Vossenberg

CERN, Genève, Geneva, Switzerland

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Publications (47)0 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: CERN, the European Organization for Nuclear Research, 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 2.8degs and a fall time of 2 ms; the first 89degs 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.
    IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008; 01/2008
  • E. Carlier, L. Ducimetiere, E. Vossenberg
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    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>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
    Power Modulator Symposium, 2006. Conference Record of the 2006 Twenty-Seventh International; 06/2006
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    ABSTRACT: The SPS LSS4 fast extraction system will serve both the anti-clockwise ring of the LHC and the long baseline neutrino (CNGS) facility. For the latter two extractions spaced by 50 ms, each affecting half of the SPS, are foreseen. During the shutdown 2003-2004 the performance of the fast extraction kickers has been improved in order to match more closely the specifications required for the CNGS and LHC extractions. The kick rise and fall times were significantly reduced, as well as the post-pulse kick ripple. However, the latter remained outside specifications and oscillations were induced in the leading bunches of the batch remaining in the machine at the moment of the first extraction. While further improving the kicker pulse shape, the possibility of damping the beam oscillations using the transverse feedback system has been explored. Recent pulse improvements and results of beam tests are reported.
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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    E. Vossenberg, G. Grawer
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    ABSTRACT: The LHC beam extraction system is composed of 15 fast kicker magnets per beam to extract the particles in one turn of the collider and to safely dispose them on external absorbers. Each magnet is powered by a separate pulse generator. The generator produces a magnet current pulse with 3 us rise time, 20 kA amplitude and 1.8 ms fall time, of which 90 us are needed to dump the beam E. B. Vossenberg et al., (2002). The beam extraction system requires a high level of reliability. To detect any change in the magnet current characteristics, which might indicate a slow degradation of the pulse generator, a high precision wideband current transformer will be installed. For redundancy reasons, the results obtained with this device will be cross-checked with a Rogowski coil, installed adjacent to the transformer. A prototype transformer has been successfully tested at nominal current levels and showed satisfactory results compared with the output of a high frequency resistive coaxial shunt. The annular core of the ring type transformer is composed of a relatively low cost commercially available nanocrystalline strip material on an iron base. The characteristic feature of this material is a structure in which a fine-crystalline grain with an average diameter of 20 nm is embedded in an amorphous residual phase. This structure gives the material a high permeability. In addition, the small strip thickness (approx. 20 μm) and the relatively high electrical resistivity, result in extremely low eddy current losses and excellent frequency behaviour. With saturation flux density of 1.2 T this material becomes even superior to Permalloys, ferrites or amorphous based alloys. In this particular application the transformer core is exposed to a unipolar induction. With normal magnetic materials this type of flux causes a relative high remanent induction. However this material allows controlling the magnetic properties, so called B-H curve shaping. It is obtained during annealing of the material by an external applied cross field and as a result the remanence ratio is less than 10%, which is excellent for this application. This paper presents the magnetic material, its incorporation in the design of the current transformer, comparative measurements of a prototype with a coaxia- l shunt precision resistor and explains why this device is an essential part of the LHC beam extraction system.
    Power Modulator Symposium, 2004 and 2004 High-Voltage Workshop. Conference Record of the Twenty-Sixth International; 06/2004
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    ABSTRACT: 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.
    Power Modulator Symposium, 2002 and 2002 High-Voltage Workshop. Conference Record of the Twenty-Fifth International; 01/2002
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    J. Bonthond, L. Ducimetiere, P. Faure, E.B. Vossenberg
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    ABSTRACT: Horizontal deflection of the beam in the dump kicker system of the CERN SPS accelerator is obtained with a series of fast pulsed magnets. The high current pulses of 50 kA per magnet are generated with capacitor discharge type generators which, combined with a resistive freewheel diode circuit, deliver a critically damped half-sine current with a rise-time of 25 μs. Each generator consists of two 25 kA units, connected in parallel to a magnet via a low inductance transmission line. Originally the pulse generators were equipped with ignitron switches. Unfortunately ignitron switches suffer sporadically from self-firing. In addition these mercury filled devices present a serious danger of environmental pollution in case of an accident. Since the development of new power semiconductor devices now offers an alternative, replacement of the ignitron switches was decided. A suitable semiconductor switch was developed with the same dimensions as the ignitron and compatible with its trigger unit. It consists of a stack of four Fast High Current Thyristor (FHCT) devices with snubber capacitors, a voltage divider and a specially designed trigger transformer. This paper gives a description of the circuit and the construction of the switches, together with measurement results, which were found to be in good agreement with simulation results.
    Pulsed Power Plasma Science, 2001. PPPS-2001. Digest of Technical Papers; 02/2001
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    ABSTRACT: CERN is constructing the Large Hadron Collider (LHC), a superconducting accelerator that will collide protons at a center of mass energy of 14 TeV. The two colliding beams will each store an energy of up to 540 MJ, which must be safely deposited within one beam revolution of 89 /spl mu/s on two external absorbers located about 700 m from the extraction points at the end of dedicated extraction tunnels. To avoid evaporation of the graphite absorber material by the very high energy density of the incident beams, the deposition area of the beams on the absorber front face will be increased. This is done by a pair of sinusoidally powered orthogonal magnet systems producing approximately an e-shape figure of about 35 mm diameter, with a minimum velocity of 10 mm//spl mu/s during the dumping process. The pulse generators of the horizontally and vertically deflecting diluter magnets are composed of capacitor banks, discharged by stacks of solid state closing switches. They are connected to the magnets by 28 m long low inductance transmission lines. The discharge switches of both generators are triggered simultaneously. The generators of the vertical magnets include additional elements to obtain an automatic phase shift of 90 degrees with respect to the horizontal magnets. The capacitor banks, charged to a voltage of 10 and 22 kV, produce a damped sinusoidal oscillation of 27 kA maximum amplitude with a period of 73 and 79 /spl mu/s. This oscillation is stopped after 90 and 115 /spl mu/s. The fast solid state closing switches are designed for a hold-off voltage of 30 kV and are of the same type as those developed for the LHC beam extraction generators.
    Power Modulator Symposium, 2000. Conference Record of the 2000 Twenty-Fourth International; 07/2000
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    ABSTRACT: A new East Fast-Extraction System is under construction in the SPS, to supply particles with a maximum batch length of 7.8 us and 10.5 us to the LHC and to CNGS (CERN Neutrino to Gran Sasso), respectively. The extraction septum magnets actually used at the SPS have been designed for slow extraction over several seconds, have large cooling and electrical power demands and need frequently maintenance in a high radiation environment. A fast system of only 250 us pulse duration has therefore been developed, using a half-sine excitation pulse with a superimposed third harmonic. The short pulse duration requires very thin magnetic yoke laminations, which can not easily be stamped and stacked. Profiting from a development for the LHC beam dump kicker magnets, the yoke is therefore built-up from tape-wound cylindrical cores, employing 50 um thick Si-steel tape. Thirty two cores are stacked longitudinally to produce a yoke of 3.2 meter length. The aperture is cut radial into each cylinder. The cores are radial compressed by spring-loaded pistons inserted in strong stainless-steel frames to provide mechanical stability. The 5+1 mm thick copper/iron septum is separated from the excitation current loop and acts as a passive eddy current screen. This allows separating the vacuum of the magnet from that of the circulating-beam channel, avoiding the need of using UHV material. This paper presents the magnet and generator prototype design as well as simulation and measurement results.
    01/2000;
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    Marcel Gyr, Eugene B. Vossenberg
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    ABSTRACT: Neutrino experiments at the SPS require short bursts of protons which are extracted by a fast resonant mechanism once or twice per cycle. The extraction process is triggered by a thyristor controlled pulse generator, discharging a capacitor bank into an extraction quadrupole. The beam being pushed onto resonance at nearly constant speed during the "linear" part of the rising ramp, the time signal of the spill (i.e. the number of particles extracted per time unit) is almost Gaussian, according to the particle distribution in the momentum and horizontal tune Q<sub>H</sub>-space. A relatively simple and inexpensive modification of the pulse generator allowed to improve this Gaussian spill time structure such as to become more rectangular.
    02/1999;
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    ABSTRACT: 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 μs flat top duration with a ripple of less than ±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 ±0.1% show that the prototype PFN conforms to the specifications and the PSpice predictions
    Pulsed Power Conference, 1999. Digest of Technical Papers. 12th IEEE International; 02/1999
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    ABSTRACT: Two LHC injection kicker magnet systems must produce a kick of 1.3 T.m each with a flattop duration of 4.25 μs or 6.5 μs, a rise time of 900 ns, and a fall time of 3 μs. The ripple in the field must be less than ±0.5%. The electrical circuit of the complete system has been simulated with PSpice. The model includes a 66 kV resonant charging power supply (RCPS), a 5 Ω pulse forming network (PFN), a terminated 5 Ω kicker magnet, and all known parasitic quantities. Component selection for the PEN was made on the basis of models in which a theoretical field ripple of less than ±0.1% was attained. A prototype 66 kV RCPS was built at TRIUMF and shipped to CERN. A prototype 5 Ω system including a PFN, thyratron switches, and terminating resistors, was built at CERN. The system (without a kicker magnet) was assembled as designed without trimming of any PFN component values. The PFN was charged to 60 kV via the RCPS operating at 0.1 Hz. The thyratron timing was adjusted to provide a 30 kV, 5.5 μs duration pulse on a 5 Ω terminating resistor. Measurement data is presented for the prototype PFN, connected to resistive terminators. A procedure has been developed for compensating the probe and oscilloscope amplifier calibration errors. The top of the 30 kV pulse is flat to ±0.3% after an initial oscillation of 600 ns total duration. The post-pulse period is flat to within ±0.1% after approximately 600 ns from the bottom of the falling edge of the pulse. A calculation was performed in which a measured 27.5 kV pulse with a 5.5 μs flattop was fed into a PSpice model of a kicker magnet with a 690 ns delay length. The resultant predicted kick rise time, from 0.2% to 99.8%, is 834 ns and the fall time 2.94 μs, for a field pulse with a flattop of 4.69 μs and a ripple of less than ±0.2%
    Particle Accelerator Conference, 1999. Proceedings of the 1999; 02/1999
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    L. Ducimetiere, G. Schroder, E. Vossenberg
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    ABSTRACT: The beam dumping system of CERN's Large Hadron Collider (LHC) is equipped with fast solid state closing switches, designed for a hold-off voltage of 30 kV and a quasi-half sine wave current of 20 kA, with 3 μs rise time, a maximum di/dt of 12 kA/μs and 2 μs fall time. The design repetition rate is 20 s. The switch is composed of ten fast high current thyristors (FHCTs), which are modified symmetric 4.5 kV GTO thyristors of WESTCODE. Recent studies aiming at improving the turn-on delay, switching speed and at decreasing the switch losses, have led to tests on an asymmetric not fully optimised GTO thyristor of WESTCODE and an optimised device of GEC PLESSEY Semiconductor (GPS), UK. The GPS FHCT, which gave the best results, is a nonirradiated device of 64 mm diameter with a hold-off voltage of 4.5 kV like the symmetric FHCT. Tests results of the GPS FHCT show a reduction in turn-on delay of 40% and in switching losses of almost 50% with respect to the symmetric FHCT of WESTCODE. The GPS device can sustain an important reverse current during a short period. This eliminates the need for an anti-parallel diode stack in the final switch. Extrapolation of the test results onto the final switch result in a turn-on delay of 600 ns and 64 J total conduction losses from turn-on to 20 kA peak current. Further tests on the GPS FHCT at 4.4 kV, 60 kA peak current and a repetition rate of 10 s resulted in a di/dt of 50 kA/μs with a turn-on delay of 700 ns. These encouraging results, obtained with a slightly modified standard device and based on several hundred thousand discharges, open a wide field of fast high current, high voltage applications where presently thyratrons and ignitrons are used
    Power Modulator Symposium, 1998. Conference Record of the 1998 Twenty-Third International; 07/1998
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    ABSTRACT: The injection kicker system of CERN's Large Hadron Collider (LHC) will consist of two sets of four kicker magnet systems each producing a magnetic field pulse of 1.3 T.m. with a duration of 6.5 μs, a rise time of 900 ns, and flat top ripple of less than ±0.5%. The electrical circuit of the complete system, including all known parasitic quantities, has been simulated with PSpice. Many parasitic elements were determined from Opera2D simulations which included eddy-currents. Equivalent circuits which simulate the frequency dependence of inductance and resistance of the Pulse Forming Network (PFN) have been derived. PSpice has been utilised to carry out a sensitivity analysis of the field to the value of both individual and groups of circuit components. Capacitors for a prototype 5 Ω PFN have been purchased and, based on the measured values of these capacitors, the diameter of the PFN coil has been re-optimised. The results of the sensitivity analysis have been used to define component tolerances for a prototype PFN. Low and high voltage measurements have commenced on the prototype PFN, and the results of the sensitivity analysis will be used to determine the source of any excessive ripple. This paper presents the results of both the analyses and measurements
    Power Modulator Symposium, 1998. Conference Record of the 1998 Twenty-Third International; 07/1998
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    ABSTRACT: A prototype of a fast pulsed eddy current septum magnet for one of the beam extraction' s from the SPS towards LHC is under development. The precision of the magnetic field must be better than 1.0 10 -4 during a flat top of 30 s. The current pulse is generated by discharging the capacitors of a LC circuit that resonates on the 1 st and on the 3 rd harmonic of a sine wave with a repetition rate of 15 s. The parameters of the circuit and the voltage on the capacitors must be carefully adjusted to meet the specifications. Drifts during operation must be corrected between two pulses by mechanically adjusting the inductance of the coil in the generator as well as the primary capacitor voltage. This adjustment process is automated by acquiring the current pulse waveform with sufficient time and amplitude resolution, calculating the corrections needed and applying these corrections to the hardware for the next pulse. A very cost-effective and practical solution for this adjustment proc...
    06/1998;
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    ABSTRACT: The injection kicker systems for the two LHC beams will each consist of four magnets and four pulse forming networks (PFNs), discharged by thyratron switches. Fast resonant charging systems (RCS) are used to charge the PFNs within 1 ms to 60 kV: fast charging minimises the number of unwanted erratically thyratron discharges. The stability and pulse to pulse reproducibility of the PFN voltage must be maintained to a precision of &les;±0.1%. Each RCS consists of a 2.4 mF primary capacitor bank, connected via a Gate Turn-Off thyristor (GTO) and a 1:23 step-up transformer to two PFNs, each with an effective capacitance of 0.96 μF. The PFNs are discharged 400 μs after the end of the charging period into the kicker magnets. The RCS include novel features such as a GTO used in Gate Assisted Turn-off (GAT) mode and a low-leakage inductance, high voltage, step-up pulse transformer. This paper presents a basic design for the RCS, and the optimisation of the electrical circuit using PSpice. The RCS are designed, constructed and tested at TRIUMF in collaboration with CERN as part of the Canadian contribution to the LHC project
    Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
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    ABSTRACT: 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
    Particle Accelerator Conference, 1997. Proceedings of the 1997; 06/1997
  • E.B. Vossenberg
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    ABSTRACT: Power semiconductors-diodes, thyristors, insulated gate bipolar transistors (IGBTs) and GTOs-are key components in pulsed power applications in the SUBT/FP-EC sections of CERN. This paper mentions these types of semiconductor devices available today and mentions future developments. Since the subject is very large, the physics of the devices are not be discussed in detail but more attention is paid to an overview concerning the device properties and applications in the pulse power circuits at CERN
    Pulsed Power '97 (Digest No: 1997/075), IEE Colloquium on; 04/1997
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    ABSTRACT: 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 &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 Ω characteristic impedance, each with a total capacitance of 0.96 μF. The PFNs 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 RCSs are designed, constructed and tested at TRIUMF in collaboration with CERN as part of the Canadian contribution to the LHC project
    Pulsed Power Conference, 1997. Digest of Technical Papers. 1997 11th IEEE International; 01/1997
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    ABSTRACT: Two sets of four LHC inflector magnet systems must produce a kick of 1.36 Tm each with a duration of 6.5 µs, a rise time of 750 ns, and an overall stability of ± 0.5%. The electrical circuit of the complete system, including all known stray quantities, has been simulated with PSpice. Many stray elements were determined from Opera2D simulations which included eddy-currents. 3D analyses have also been carried out for the kicker magnet using the electromagnetic analysis code Opera3D. Equivalent circuits which simulate the frequency dependence of inductance and resistance of the Pulse Forming Network (PFN) have been derived. The dimensions of the PFN coil have been selected to give the correct pulse response. The end cells of the PFN have also been optimised. The discharge stability of various PFN capacitors has been measured. This paper presents the results of both the analyses and measurements.
    12/1996;
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    ABSTRACT: CERN, the European Laboratory for Particle Physics, has started construction of the Large Hadron Collider (LHC), a superconducting accelerator that will collide protons at a center of mass energy of 14 TeV from the year 2005 onwards. The kicker magnet pulse generators of the LHC beam extraction system require fast high power switches. One possible type is the pseudospark switch (PSS) which has several advantages for this application. A PSS fulfilling most of the requirements has been developed in the past years. Two outstanding problems, prefiring at high operating voltages and sudden current interruptions (quenching) at low voltage could have been solved recently. Prefiring can be avoided for this special application by conditioning the switch at two times the nominal voltage after each power pulse. Quenching can be suppressed by choosing an appropriate electrode geometry and by mixing Krypton to the D<sub>2</sub> gas atmosphere. One remaining problem, related to the required large dynamic voltage range (1.7 kV to 30 kV), is under active investigation; steps in forward voltage during conduction, occurring at low operation voltage at irregular time instants and causing a pulse to pulse jitter of the peak current. This paper presents results of electrical measurements concerning prefiring and quenching and explains how these problems have been solved. Furthermore the plans to cure the forward voltage step problem are discussed
    Power Modulator Symposium, 1996., Twenty-Second International; 07/1996