Methods and results of modeling and transmission-line calculations of the superconducting dipole chains of CERN's LHC collider

Electrical modeling and simulation of the LHC magnet strings are being used to determine the key parameters that are needed for the design of the powering and energy extraction equipment. Poles and zeros of the Laplace expression approximating the Bode plot of the measured coil impedance are used to synthesize an R/L/C model of the magnet. Subsequently, this model is used to simulate the behavior of the LHC main dipole magnet string. Lumped transmission line behavior, impedance, resonance, propagation of the power supply ripple, ramping errors, energy extraction transients and their damping are presented in this paper. (3 refs)

Evaluation of Impact from Ripple and Transient Phenomena in the LHC Dipole Strings

Based on measurements of the A.C. electrical characteristics of prototype magnets, synthesized computer models of the principal, individual, superconducting magnetic elements of the Large Hadron Collider have been elaborated. The models constitute the basic elements for the determination of the transfer functions of the magnet chains. This tool provides the possibility to evaluate the resonance spectrum of the chains and to determine the needs for additional damping. Results of the analysis of transmission line effects in the LHC main dipole chains are presented. In particular, data from ripple calculations and ramping studies are discussed. Computer simulations of the quench protection circuit provide information about the transient phenomena occurring in the dipole chains during normal operation of the fast de-excitation switches and under abnormal conditions

A 20 kA Test Bench for High-Precision Current Measurements

The d.c. currents in the LHC dipole and quadrupole chains will require settings and adjustments with a precision of a few ppm. For an ultimate current level of 13 kA this represents an unprecedented accuracy. Compared to the requirements of previous accelerators at CERN, such as the LEP, this is a factor of ten better in accuracy at more than twice the current. State-of-the-art, zero-flux current transducers from Industry will be used for the precision measurements. As no existing laboratory would be capable of performing the calibrations of these transducers to the required precision, a major upgrading of the current Standards laboratory at CERN was decided. The paper describes the various phases of the project, from field calculations and design to construction and final commissioning of this unique test bench. The highly automated facility allows determination of off-sets, linearity and drift of transducers up to 20 kA but provides equally the means to study the sensitivity of the transducers to external stray fields as generated by currents in adjacent busbars

Electronic Systems for the Protection of Superconducting Devices in the LHC

The Large Hadron Collider LHC [1] incorporates an unprecedented amount of superconducting components: magnets, bus-bars, and current leads. Most of them require active protection in case of a transition from the superconducting to the resistive state, the so-called quench. The electronic systems ensuring the reliable quench detection and further protection of these devices have been developed and produced over the last years and are currently being put into operatio

Results from Commissioning of the Energy Extraction Facilities of the LHC Machine

The risk of damage to the superconducting magnets, bus bars and current leads of the LHC machine in case of a resistive transition (quench) is being minimized by adequate protection. The protection is based on early quench detection, bypassing the quenching magnets by cold diodes, energy density dilution in the quenching magnets using heaters and, eventually, energy extraction. For two hundred and twenty-six LHC circuits (600 A and 13 kA) extraction of the stored magnetic energy to external dump resistors was required. All these systems are now installed in the machine and the final hardware commissioning has been undertaken. After a short description of the topology and definitive features, layouts and parameters of these systems the paper will focus on the results from their successful commissioning and an analysis of the system performance

Cooling process of the LHC energy extraction resistors

The energy stored in all the LHC dipoles, about 11 GJ, can potentially cause severe damage to the magnets, bus bars and current leads. In order to protect the superconducting elements after a resistive transition, the energy is dissipated into dump resistors switched in series with the magnet chains. This paper describes the cooling process of the resistors and explains the choice process for the main components of the cooling equipment

Energy Extraction for the LHC Superconducting Circuits

The superconducting magnets of the LHC will be powered in about 1700 electrical circuits. The energy stored in circuits, up to 1.3 GJ, can potentially cause severe damage of magnets, bus bars and current leads. In order to protect the superconducting elements after a resistive transition, the energy is dissipated into a dump resistor installed in series with the magnet chain that is switched into the circuit by opening current breakers. Experiments and simulation studies have been performed to identify the LHC circuits that need energy extraction. The required values of the extraction resistors have been computed. The outcome of the experimental results and the simulation studies are presented and the design of the different energy extraction systems that operate at 600 A and at 13 kA is described

Modeling and Computer Simulation of the Pulsed Powering of Mechanical D.C. Circuit Breakers for the CERN/LHC Superconducting Magnet Energy Extraction System

This article presents the results of modeling and computer simulation of non-linear devices such as the Electromagnetic Driver of a D.C. Circuit Breaker. The mechanical and electromagnetic parts of the Driver are represented as equivalent electrical circuits and all basic processes of the Driver's magnetic circuit are calculated

Upgrade of the protection system for superconducting circuits in the LHC

Prior to the re-start of the Large Hadron Collider LHC in 2009 the protection system for superconducting magnets and bus-bars QPS will be substantially upgraded. The foreseen modifications will enhance the capability of the system in detecting problems related to the electrical interconnections between superconducting magnets as well as the detection of so-called aperture symmetric quenches in the LHC main magnets

Energy Extraction Resistors for the Main Dipole and Quadrupole Circuits of the LHC

When the LHC will be operating at its maximum beam energy, its superconducting dipole chains store a total magnetic energy of more than 11 GJ. At the same time, the QF and QD quadrupole circuits store a total energy of 400 MJ. Even with the sectorisation of each of the three principal power circuits into eight individually powered segments, the stored energy of a single circuit is considerable. During normal operation the energy in the dipole circuits is safely returned to the mains grid, using the thyristor-based, 'booster' unit of the power converters, operating in inversion. For the quadrupole chains, where the converter is of a mono-polar topology, the stored energy is dissipated into the resistive part of the warm d.c. power lines (busbars and cables) in a slow, controlled run-down. When a magnet quenches, however, such a slow energy transfer, taking 20 minutes from the rated LHC current, will not be possible. The 'cold' diode, taking over the magnet current in case of a quench, will not survive this slow current decay. For this reason, energy extraction facilities will be inserted into the power circuits. These systems are being designed to absorb the total circuit energy and de-excite the chains with a current decay time constant of 104 s for the dipoles and 40 s for the quadrupoles. The resulting maximum decay rates (-125 A/s and -325 A/s respectively) are comfortably below the levels where quench-back will occur. The energy extraction systems are based on an array of special, mechanical d.c. circuit breakers and absorber resistors, which are switched into the circuit by opening of the breakers. The design and construction of these large power resistors of a unique concept are the topics of this paper. The project is being realised as collaboration between, IHEP-Protvino, CERN and European Industry