Frederick Bordry

A novel 60 MW pulsed power system based on capacitive energy storage for particle accelerators

Large Physics experimentation as in particle accelerators or in nuclear fusion is often characterised by a strong and modulated power demand, incompatible with the power availability of the grid. Therefore, large facilities for short-term energy storage have been used, traditionally based on rotating machine. Several new solutions of power supply are studied and especially a new solution for energy storage is presented, where capacitors are used as energy storage elements. They are integrated in the static power converter. The energy- and instantaneous power-demand are presented, and then the global storage system with a dedicated multilevel DC/DC converter with flying capacitors is described. A specific control strategy for voltage balance, together with an adapted loss compensation method is also introduced and developed.

The Energy calibration of LEP in the 1993 scan

This report summarizes the procedure for providing the absolute energy calibration of the LEP beams during the energy scan in 1993. The average beam energy around the LEP ring was measured in 25 calibrations with the resonant depolarization technique. The time variation of this average beam energy is well described by a model of the accelerator based on monitored quantities. The absolute calibration of the centre of mass energies of the off-peak points is determined with a precision of 2 parts in 105 resulting in a systematic error on the Z-mass of about 1.4 MeV and on the Z-width of about 1.5 MeV.

A Multilevel Power Converter with Integrated Storage for Particle Accelerators

The PS accelerator (proton-synchrotron) at CERN (European Organization for Nuclear Research) is composed of one hundred magnets connected in series. During a cycle of 2.4 seconds, the active power at the magnets terminals varies from plus to minus 40 MW. As this large active power variation was not acceptable to the electrical network, a motor-generator set (M-G) was inserted between the grid and the load in 1968. The M-G set acts as a fly-wheel with a stored kinetic energy of 233 MJ and the magnets are fed by two 12-pulse thyristor rectifiers. After forty years of operation, the system has to be replaced. This paper presents a possible solution for a power system based on capacitive storage.

A 4-quadrant 300kW-peak high precision and bandwidth switch mode power converter for particle accelerator magnets supply

A switch mode AC/DC-DC power conversion topology is proposed for the supply of particle accelerator correction magnets, requiring simultaneously high peak power (300 kW), high bandwidths (1 kHz in voltage, 300 Hz in current), high current precision (10-4), EMC emissions according to international standards and current/voltage reversibility (4-quadrants operation). The power part dimensioning key issues are presented, including semiconductor power cycling design, high frequency power filtering, DC-link bus stability analysis. The feedback controls strategy and suited PWM techniques are reported. Experimental results are presented and commented.

Power converters for particle accelerators

In 1905 Albert Einstein wrote his legendary articles which provided the basis for three fundamental fields in physics: the theory of special relativity, quantum theory and the theory of Brownian motion. Subsequently, particle physics made dramatic progress in the understanding of the fundamental forces and particles, and underlying symmetries of nature. These achievements were based on intensive interaction between the development of powerful theories, experimental discoveries and precision measurements with particle accelerators. Power converters play a crucial role in accelerators and the evolution of power electronics is one of the important ingredients that has allowed the attainable energy to be increased by a large factor every decade. This exponential growth has enabled physicists to resolve ever smaller objects and to produce ever heavier particles. For every new generation of accelerators, improvements in beam quality impose new and more severe requirements on power converter performance. In response, a more diverse set of converter ratings and topologies are necessary; from watts to megawatts and from pulsed to DC. This paper highlights specific power converter applications that illustrate the evolution of power electronics used in particle accelerators. It also presents the future challenges facing the power electronics community in response to the demands of the particle physicists

Dynamic effects and their control at the LHC

Tune, chromaticity and orbit of the LHC beams have to be precisely controlled by synchronising the magnetic field of quadrupole, sextupole and corrector magnets. This is a challenging task for an accelerator using superconducting magnets, whose field and field errors will have large dynamic effects. The accelerator physics requirements are tight due to the limited dynamic aperture and the large energy stored in the beams. The power converters need to be programmed in order to generate the magnetic functions with defined tolerances. During the injection process and the energy ramp the magnetic performance cannot be predicted with sufficient accuracy, and therefore real-time feedback systems based on magnetic measurements and beam observations are proposed. Beam measurements are used to determine a correction factor for some of the power converters. From magnetic measurements the excitation of small magnets to compensate the sextupolar (b/sub 3/) and decapolar (b/sub 5/) field components in the dipole magnets will be derived. To meet these requirements a deterministic control system is envisaged.

The commissioning of the LHC test string 2

String 2 is a full-size model of an LHC cell of the regular part of the arc. It is composed of six dipole magnets with their correctors, two short straight sections with their orbit and lattice corrector magnets, and a cryogenic distribution line running alongside the magnets. The commissioning of String 2 Phase 1, with one half-cell and the following quadrupole, has started in April 2001. As for String 1, the facility was built to individually validate the LHC systems and to investigate their collective behaviour during normal operation (pumpdown, cool-down and powering) as well as during exceptional conditions such as quenches. String 2 is a stepping stone towards the commissioning of the first sector (one eight of LHC) planned for 2004. It is expected to yield precious information on the infrastructures, the installation, the tooling and the procedures for the assembly, the testing and the commissioning of the individual systems, as well as the global commissioning of the technical systems. This paper describes the procedures followed for the commissioning and details the preparation for the first cool-down and for the powering.

The LHC magnet string programme: status and future plans

String 1, with one twin aperture quadrupole and three twin aperture 10-m dipoles (MB1, MB2 and MB3) powered in series and operating at 1.9 K, has recently been dismantled after four years of operation interrupted by technical stops and shutdowns for upgrading or exchanging equipment. Following the validation of the main LHC systems (cryogenics, magnet protection, vacuum, powering and energy extraction) the experimental programme was oriented towards the optimisation of the design and the observation of artificially induced fatigue effects. The design study for String 2 has been completed. This facility, which will be commissioned in December 2000, is composed of two LHC half-cells each consisting of one twin aperture quadrupole and three 15-m twin aperture dipoles. A cryogenic distribution line housing the supply and recovery headers runs parallel to the string of magnets. An electrical feedbox is used to power, with high temperature superconductor current leads, the circuits as in the regular part of an LHC arc. This paper reviews the experiments carried-out with String 1 and summarises the results obtained after more than 12800 hours of operation below 1.9 K and 172 quenches. It also describes the layout and the components of String 2 and explains the objectives pursued by its designers.

Effects of tidal forces on the beam energy in LEP

The e/sup +/e/sup -/ collider LEP is used to investigate the Z particle and to measure its energy and width. This requires energy calibrations with /spl sim/20 ppm precision achieved by measuring the frequency of a resonance which destroys the transverse beam polarization established by synchrotron radiation. To make this calibration valid over a longer period all effects causing an energy change have to be corrected for. Among those are the terrestrial tides due to the Moon and Sun. They move the Earth surface up and down by as much as /spl sim/0.25 m which represents a relative local change of the Earth radius of 0.04 ppm. This motion has also lateral components resulting in a change of the LEP circumference (C/sub c/=26.7 km) by a similar relative amount. Since the length of the beam orbit is fixed by the constant RF-frequency the change of the machine circumference will force the beam to go off-center through the quadrupoles and receive an extra, deflection leading to an energy change given by /spl Delta/C/sub cC/sub cspl sim/-(/spl alphasub cspl Deltasub c/E/E. With the momentum compaction /spl alphasub c/=1.85 10/sup -4/ for the present LEP optics this gives tide-driven p.t.p. Energy excursion up to about 220 ppm, corresponding to /spl sim/18.5 MeV for the Z energy. A beam energy measurement carried out over a 24 hour period perfectly confirmed the effects expected from a more detailed calculation of the tides. A corresponding correction can be applied to energy calibrations.<<ETX>>

Development, test and large production of soft switching high current power converters for particle accelerators

The large hadron collider (LHC) is the next particle accelerator being constructed on the CERN site. The 27 km long accelerator requires many high current (multi-kA) power converters to supply the superconducting magnets. This paper describes the development of a modular high current power converter, capable of supplying up to [8 kA, 8 V] using several current sources of [2 kA, 8 V] in parallel. Production aspects and test results of 200 power converters are presented and analysed