Krainz, G Quench Protection and Powering in a String of Superconducting Magnets for the Large Hadron Collider Practical experience has been attained on the LHC Test String (String~1), composed of one 3~m long superconducting twin-aperture prototype quadrupole and three 10~m long superconducting twin-aperture prototype dipoles. The protection diodes are housed in the cold mass of the short straight section. The quench protection system acts on the half-cell level. During the operation of the LHC Test String, magnet quenches have been provoked manually by firing the quench heaters or occured manually by exceeding the critical temperature or critical current density of the superconductor. Most of the data could be measured while some parameters (magnet current, diode current, average temperature, etc.) cannot be directly measured. A simulation progam has been developed to calculate the missing data. The validation of the model has been performed by comparing measured and simulated data. The modelling of the quench behaviour of the final version of the LHC magnets show that hot-spot temperatures and voltages to ground can be kept within safe limits as long as the variations in heater delay values of RRR are not too large. eng CERN Geneva 1997

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2002-003; http://cds.cern.ch/record/537775/files/thesis-2002-003.pdf; http://cds.cern.ch/record/537775/files/thesis-2002-003.ps.gz;

Imported from Invenio. Wikus, P Dilution Refrigeration of Multi-Ton Cold Masses Dilution refrigeration is the only means to provide continuous cooling at temperatures below 250 mK. Future experiments featuring multi-ton cold masses require a new generation of dilution refrigeration systems, capable of providing a heat sink below 10 mK at cooling powers which exceed the performance of present systems considerably. This thesis presents some advances towards dilution refrigeration of multi-ton masses in this temperature range. A new method using numerical simulation to predict the cooling power of a dilution refrigerator of a given design has been developed in the framework of this thesis project. This method does not only allow to take into account the differences between an actual and an ideal continuous heat exchanger, but also to quantify the impact of an additional heat load on an intermediate section of the dilute stream. In addition, transient behavior can be simulated. The numerical model has been experimentally verified with a dilution refrigeration system which has been designed, built and tested at CERN in the framework of this doctoral thesis project. Furthermore, the determination of the residual heat load to the cold mass of a very low temperature (VLT) experiment is addressed. The results of this analysis can be used to predict the required cooling power for large future experiments. Based on the experience gained with the dilution refrigeration system at CERN, design rules for large dilution refrigerators have been derived. They are consequently used in a design and feasibility study of a refrigeration system, which is tailored for the future cryogenic dark matter search EURECA and meets the requirements of low background experiments and operation in remote underground laboratories. This doctoral thesis project has been funded CERN and by the Austrian Federal Ministry for Education, Science and Culture. eng Wien TU Vienna 2007

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2007-040; http://cds.cern.ch/record/1036217/files/thesis-2007-040.pdf;

Imported from Invenio. La China, M Shape Stability of the LHC Superconducting Dipole: Mechanical Model and Experimental Investigations The aim of this work is the study of the geometry of the main superconducting dipole for the Large Hadron Collider from the manufacturing process throughout the pre-operative stages to predict the respect of the tight tolerance, imposed by the beam dynamic, in both nominal and chancy working conditions. Expected and unexpected situations have been approached through the development of dedicate models and tests with the purpose of evaluating their impact on magnet geometry. In our study we used structural models of different complexity for different purposes. For example we used analytical models in conjunction with the cold mass geometry database to simulate the overall effect of individual geometry corrections or to discriminate elastic from inelastic measured deformations. By means of finite element models, instead, we investigated the effect of mechanic loads as induced by road transport, or the effect of electro-magnetic forces arising in working conditions. As the assembly complexity prevents from deducing some of the main mechanical properties we set-up different tests and we evaluated the desired properties from the comparison with analytical or finite element models. eng Genoa U. Genoa 2006

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2007-036; http://cds.cern.ch/record/1034374/files/thesis-2007-036.pdf;

Imported from Invenio. Bettoni, S Design and integration of superconducting undulators for the LHCbeam diagnostics eng Milano U. Milano 2006

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2006-071; http://cds.cern.ch/record/1005179/files/thesis-2006-071.pdf;

Imported from Invenio. Tratnik, H Electron Stimulated Desorption of Condensed Gases on Cryogenic Surfaces In ultra-high vacuum systems outgassing from vacuum chamber walls and desorption from surface adsorbates are usually the factors which in°uence pressure and residual gas composition. In particular in beam vacuum systems of accelerators like the LHC, where surfaces are exposed to intense synchro- tron radiation and bombardment by energetic ions and electrons, properties like the molecular desorption yield or secondary electron yield can strongly in°uence the performance of the accelerator. In high-energy particle accelerators operating at liquid helium temperature, cold surfaces are exposed to the bombardment of energetic photons, electrons and ions. The gases released by the subsequent desorption are re-condensed on the cold surfaces and can be re-desorbed by the impinging electrons and ions. The equilibrium coverage reached on the surfaces exposed to the impact of energetic particles depends on the desorption yield of the condensed gases and can a®ect the operation of the accelerator by modifying the secondary electron yield of these surfaces. The desorption yields under electron impact of various gases condensed on a copper surface cooled at 4.2K have been measured and will be presented together with the values of the sticking coe±cient of these gases on a 4.2K condensing surface. A model to explain the variation of the desorption yields with the surface coverage will also be described. In this work the electron stimulated desorption yield (ESDY) at cryogenic temperatures has been measured. This parameter is of importance to un- derstand and predict the vacuum behavior in the LHC, in the presence of an electron cloud, as in that case the electron induced desorption will be the main gas source. Of particular interest is the variation of the electron induced desorption yield with the gas coverage as most gases (with the exception of hydrogen) condense on the beam screen surface, which leads to an increased density of molecules per unit area. The measurement of the ESDY requires a measuring system where ¯rst a known amount of electrons can be accelerated to a target cooled at helium temperature, second the nature and the number of desorbed molecules can be measured and third a predetermined quantity of gas can be injected and condensed on the cold target. eng Vienna, Tech. U. Vienna 2005

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2006-038; http://cds.cern.ch/record/976630/files/thesis-2006-038.pdf;

Imported from Invenio. Schwerg, N Electromagnetic Design Study for a Large Bore 15T Superconducting Dipole Magnet In the framework of research and development (R&D) activities at CERN the Next European Dipole (NED) program is one which is to the development of a high-field dipole magnet using Nb_3Sn superconductors. Part of the NED activities is a design study of different possible dipole configurations which is shared amongst the collaborating institutes. This thesis covers the electromagnetic design study of an 88 mm large bore superconducting 15 T dipole magnet with a coil cross section in cos-theta-layer design. Based on analytically describable geometries the sources of multipole errors are studied and elementary estimations of the magnet are carried out, e.g., the required amount of superconductors or the influence of the iron yoke thickness on the field quality. The magnet cross section for NED is optimized by means of the CERN field computation program ROXIE. The preliminary NED design serves as starting point for the coil cross section optimization with respect to field quality and a radial positioning of the conductor blocks. Due to the high field of magnetic induction, the surrounding iron yoke saturates for high transport currents and the multipole errors vary with excitation. In order to reduce the variation, modifications of the iron yoke shape are studied, like, e.g., holes punched into the yoke laminations, a change of the outer yoke contour or an inner contour of elliptical shape. For an elliptically shaped inner iron yoke contour the coil cross section is again optimized resulting in the Reference Design V. 2 for the NED collaboration. The persistent current induced field errors are estimated for the present design and NED cable. Based on these results different compensation methods are investigated including ferromagnetic shims inside the cables, mounted on the cold bore tube or on the copper wedges. eng Berlin TU Berlin 2005

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2005-055; http://cds.cern.ch/record/914515/files/thesis-2005-055.pdf;

Imported from Invenio. Lozano Bernal, María Pilar Estudio de la desorción estimulada por iones de adsorbatos en superficies de interés tecnológico (Al, Cu) spa Madrid U. Madrid 2004

http://cds.cern.ch/record/817301/files/Thesis-2004-LozanoBernal.pdf;

Imported from Invenio. Vergara-Fernández, A Reliability of the Quench Protection System for the LHC Superconducting Elements The huge energy stored in the Large Hadron Collider (LHC) could potentially cause severe damage when the superconducting state disappears (quench) if precautions are not taken. Most of the superconducting elements in this accelerator require protection in case of resistive transition. The reliability of the Quench Protection System will have a very important impact on the overall LHC performance. Existing high energy accelerators were conceived as prototypes whose main objective was not the efficiency but to push the performance to the limit. The LHC will be the first large accelerator with reliability oriented design. This thesis focuses on adapting the reliability theory and methods that are currently used by the industry and small accelerators to the protection systems of larger and more complex machines like the LHC. Two main contributions have been achieved. Firstly, the author has developed an analytical model for a general multi-state protection system, which is able to include the specific characteristics of a large superconducting accelerator. In order to provide a tool for its implementation and related computations, the simulation program RESQP (REliability Software for Quench Protection studies) has been developed. Secondly, a theoretical and experimental analysis of the LHC Quench Protection System dependability has been carried out. eng CERN Geneva 2003

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2004-019; http://cds.cern.ch/record/740804/files/thesis-2004-019.pdf;

Imported from Invenio. Haverkamp, M Decay and Snapback in Superconducting Accelerator Magnets This thesis deals with the explanation and compensation of the effects 'decay' and 'snapback' in superconducting accelerator magnets, in particular in those used in the new Large Hardron Collider at CERN. During periods of constant magnet excitation, as for example during the injection of particles in the storage ring, the magnetic field in superconducting accelerator magnets shows a decay behavior. As soon as the particles are accelerated, the magnets are ramped, and the magnetic field 'snaps back' to the original hysteresis curve. Decay and snapback affect the beam in the machine and have tobe compensated precisely in order to avoid losses of particles. The research presented in this thesis is a step towards a better understanding of 'decay' and 'snapback' in superconducting particle accelerators. The thesis provides tools for the prediction and compensation of both effects in the magnets, and for the analysis of correlations between different magnet parameters. eng Twente U., Enschede Enschede 2003

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2003-030; http://cds.cern.ch/record/677979/files/thesis-2003-030.pdf;

Imported from Invenio. Schnizer, P Measuring system qualification for LHC arc quadrupole magnets Currently the LHC Project at CERN has reached the construction phase. The superconducting magnets of this new accelerator work at superfluid helium temperature. The "arc quadrupoles" (360 pieces), which focus the beam have to be measured at a temperature of 1.9 Kelvin with outstanding precision: The measurement aims to reach a reproducibility of 1.5 · 10^-4 for the field integral, 2 ppm for the harmonic content of the main field and 0.15mm for the position of the axis. A specially developed scanner allows the simultaneous measurement of the field axis and quality. This thesis demonstrates that the system as it stands fulfils the high requirements with respect to the magnetic measurement and the magnetic axis and thus provides the desired unique versatile equipment. The assessment was performed based on experimental results, direct calibration and using a new simulation tool. The main defects treated are mechanical torsion and vibration of moving parts, electrical noise and power supply ripple. eng CERN Geneva 2002

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2003-006; http://cds.cern.ch/record/605602/files/thesis-2003-006.pdf;

Imported from Invenio. Milani, D Quench propagation in High Temperature Superconducting materials integrated in high current leads High temperature superconductors (HTS) have been integrated in the high current leads for the Large Hadron Collider (LHC), under construction at CERN, in order to reduce the heat leak into the liquid helium bath due to the joule effect. The use of the HTS technology in the lower part of the current leads allowed to significantly reduce the heat charge on the cryogenic system. Hybrid current leads have been designed to fulfill the LHC requirements with respect to thermal load; several tests have been performed to study the lead behavior especially during a quench transient. Quench experiments have been performed at CERN on 13 kA prototypes to determine the adequate design and protection. In all the tests it is possible to know the temperature profile of the HTS only with the help of quench simulations that model the thermo-hydraulic processes during quench. The development of a theoretical model for the simulation allows reducing the number of test to perform and to scale the experimental result to other current lead sizes. In this work a theoretical quench model and a numerical code have been developed to compute the quench process and the thermal analysis in the HTS part of the current leads. The model approximates the heat balance equations with the finite difference method and considers the temperature dependence of material's properties. With this model it is possible to perform a thermal analysis of the HTS assembly in steady working condition as well as to study the resistive transition known as quench. The numerical approach is much more accurate than the analytical one, which involves a more approximated model with more physical approximations. In this work are given: the theoretical description of the model, its numerical implementation, the experimental validation and some simulation results. eng CERN Geneva 2001

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2002-015; http://cds.cern.ch/record/548605/files/thesis-2002-015.pdf; http://cds.cern.ch/record/548605/files/thesis-2002-015.ps.gz;

Imported from Invenio. Vorlaufer, G Modification of Ultra-High Vacuum Surfaces Using Free Radicals In ultra-high vacuum systems outgassing from vacuum chamber walls and desorption of surface adsorbates are usually the factors which determine pressure and residual gas composition. In particular in beam vacuum systems of accelerators like the LHC, where surfaces are exposed to intense synchrotron radiation and bombardment by energetic ions and electrons, surface properties like the molecular desorption yield or secondary electron yield can strongly influence the performance of the accelerator. Well-established treatment methods like vacuum bake-out or glow-discharge cleaning have been successfully applied in the past to condition ultra-high vacuum surfaces, but these methods are sometimes difficult to carry out, for example if the vacuum chambers are not accessible. In this work, an alternative treatment method is investigated. This method is based on the strong chemical reactivity of free radicals, electrically neutral fragments of molecules. Free radicals (in the case of this work, nitrogen and oxygen radicals) are generated in a microwave plasma source and pumped through a vacuum chamber where they can react with the surface in various ways, thereby removing surface adsorbates and/or changing the chemical composition of the surface. In order to assess the effect of radical treatment, surfaces of radical treated samples have been analysed using various techniques and compared with surfaces of non-treated samples of the same material. Special emphasis has been put on the measurement of the molecular desorption yield. For this purpose an experimental vacuum system has been set up which permits measurements of the molecular desorption yield induced by electron bombardment (ESD) \emph{in situ}, i.e. without exposing the sample to atmosphere between radical treatment and measurement. In view of a possible application to accelerator beam pipes, the distribution of radicals in cylindrical tubes has been studied in detail by means of a computer simulation whose underlying physical model incorporates concepts of fluid dynamics and chemical kinetics. Radical distributions have also been determined experimentally from measurements of the heat of recombination. Results of these measurements are compared with those from the computer simulation. This work has been carried out in the vacuum group of the LHC division at CERN with the aim to investigate the radical treatment method in general and its application for the conditioning of surfaces in the LHC beam vacuum system in particular. With the experimental and simulation results presented in this work, it is possible to demonstrate capabilities and limitations of the radical treatment method and to specify favourable operating conditions for practical applications. eng CERN Geneva 2002

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2002-014; http://cds.cern.ch/record/547706/files/thesis-2002-014.pdf; http://cds.cern.ch/record/547706/files/thesis-2002-014.ps.gz;

Imported from Invenio. Schreiner, T Current distribution inside Rutherford-type superconducting cables and impact on performance of LHC dipoles The windings of high--field superconducting accelerator magnets are usually made of Rutherford--type cables. The magnetic field distribution along the axis of such magnets exhibits a periodic modulation with a wavelength equal to the twist pitch length of the cable used in the winding. Such a Periodic Field Pattern (PFP) has already been observed in number of superconducting accelerator magnets. Additional unbalanced currents in individual strands of the cable appear to be causing this effect. The present thesis describes the investigation of the PFPs performed with a Hall probes array inserted inside the aperture of the LHC superconducting dipoles, both in the small--scale model magnets with a length of one meter and in full--scale prototypes and pre--series magnets with fifteen meters of length. The amplitude and the time dependence of this periodic field oscillation have been studied as a function of the magnet current history. One of the main parameters influencing the properties of the PFP is the cross--contact resistance between the strands of the cable. An estimation for these values is achieved by the so--called Field Advance (FA) measurements performed again with a Hall probes set--up. Due to eddy currents a difference in the field values for the ramp--up and the ramp--down of a current cycle is generated, which is a linear function of the applied ramp rate. The resulting slope is furthermore indirectly proportional to the corresponding cross--contact resistance. Two types of so--called interstrand coupling currents, uniform and non--uniform, are induced by a changing magnetic field and flow not only within the individual strands but also between the strands of the cable. Therefore some parts of the strands can carry a total current which is larger than the transport current. This phenomenon locally reduces the difference between the total strand current and the critical current of the superconductor and can provoke a premature quench of the superconducting magnet, i.e. a transition to the normal state. Considering theoretical models and experimental results the impact of the current distribution on the quench performance of the LHC dipoles is discussed. Finally an estimation for the influence of these currents on the magnet stability with respect to quench during operation conditions is given. eng CERN Geneva 2002

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2002-006; http://cds.cern.ch/record/539635/files/thesis-2002-006.pdf; http://cds.cern.ch/record/539635/files/thesis-2002-006.ps.gz;

Imported from Invenio. Verweij, A P Electrodynamics of superconducting cables in accelerator magnets eng Twente U. Twente 1995

http://cds.cern.ch/record/292595/files/Thesis-1995-Verweij.pdf;

Imported from Invenio. Hatchadourian, E Thermohydraulique des écoulements d'hélium faiblement supercritique en conduite: application au refroidissement des écrans de faisceau du LHC Au cours d'observations, au-delà de la mise en évidence d'un effet inattendu, l'effort de compréhension porte tout d'abord vers une description qualitative du phénomène et ensuite quantitative. Puis, lorsque ce phénomène est compris, le travail peut s'orienter vers une étape d'exploitation o le mécanisme est utilisé pour développer de nouvelles voies de recherche ou encore apporter des solutions à des besoins d'ordre technologique. L'étude établie sur le projet du futur collisionneur de particules du CERN en est un exemple convaincant : il s'agit dans un premier temps de définir un modèle simplifié sur l'écoulement d'hélium supercritique dans des tubes soumis à des apports de chaleur, afin de permettre la compréhension des mécanismes essentiels puis developper un modèle plus précis, mais également plus complet, pour l'étude quantitative. L'application directe de cette étude thermohydraulique concerne le refroidissement des écrans de faisceau du LHC. Ces écrans, maintenus à une température comprise approximativement entre 5 K et 20 K par circulation d'hélium supercritique dans de longs et étroits tubes, seront installés dans les ouvertures des électro-aimants supraconducteurs dans le but d'intercepter les charges thermiques dynamiques. Cette solution permet d'éviter le régime diphasique mais présente néanmoins un risque d'instabilité thermohydraulique... fre 2000

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2001-009; http://cds.cern.ch/record/504486/files/thesis-2001-009.pdf; http://cds.cern.ch/record/504486/files/thesis-2001-009.ps.gz;

Imported from Invenio. Sonnemann, F Resistive transition and protection of LHC superconducting cables and magnets Superconductivity and superfluidity are macroscopic quantum-effects that are used in technology. One of the most important applications of superconductivity is the design of strong magnets, which guide particles at very high energies in circular accelerators. In the Large Hadron Collider (LHC), which is being constructed at the European Laboratory for Particle Physics (CERN) close to Geneva, magnets wound with conventional superconductors are cooled with superfluid helium to access even higher magnetic field strengths. The resistive transition from the superconducting to the normal-conducting state (known as a quench) can be characterised by mechanical, electrodynamic and thermodynamic processes. Due to the high amount of stored magnetic energy, a quench can potentially cause damage in superconducting elements by overheating or excessive voltages. A detailed description of the related mechanisms is needed to understand the quench process better and to design a reliable protection system. This requires analytical and more importantly numerical models, which include the heat generation of the superconductor, cooling by helium, the thermodynamic propagation of the normal-conducting zone, as well as the impact of induced eddy currents. In the framework of this thesis, a new numerical algorithm has been developed. The improvements and advancements made in the quench modelling are explained in this thesis. It also includes detailed analyses and simulation studies of the quench processes in LHC superconducting cables and magnets. The LHC protection system that has been optimised by the outcome of this thesis is presented. The results and consequences of the performed analyses and simulations are summarised. eng CERN Geneva 2001

http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2001-004; http://cds.cern.ch/record/499591/files/thesis-2001-004.pdf; http://cds.cern.ch/record/499591/files/thesis-2001-004.ps.gz; http://cds.cern.ch/record/499591/files/thesis-2001-004_phd.thesis.ps.gz;

Imported from Invenio. Komorowski, P A Electro-topological analysis and diagnostics of the superconducting magnet systems for the Large Hadron Collider eng CERN Geneva 2000

http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=CM-P&id=CM-P00068853; http://cds.cern.ch/record/497232/files/CM-P00068853.pdf;

Imported from Invenio. Ramberger, S Conceptual design of superconducting magnets for the LHC using genetic optimization algorithms eng Wien TU Wien 1999

http://cds.cern.ch/record/492618/files/cer-002247074.pdf;

Imported from Invenio. Vlachoudis, V Taux De Capture De Fission Du $^{232}$th, $^{238}$u, $^{237}$np Et $^{239}$pu Par Des Neutrons De Spallation Dans Un Grand Massif De Plomb eng Bordeaux 1. Cent. Etud. Nucl. Talence 1999

Imported from Invenio. Pivi, M Beam Induced Electron Multipacting in the CERN Large Hadron Collider Accelerator LHC Electron multiplication driven by the electric field of the proton bunches is expected to occur in the Large Hadron Collider (LHC), according to previous studies performed at CERN with two computer simulation codes. Electrons, secondary electrons and photo-electrons created by the beam will be accelerated in the electric field of the proton beam and will produce a large heat load at the surface, space charge in the chamber, coupling between the electrons and the beam and a pressure increase, which ultimately could cause the loss of the proton beam. It is, therefore, fundamental to study the phenomenon. The Ph.D. thesis work included studies and planning for the laboratory experimental setup to reproduce the electron multipacting induced by radio frequency, performing data aquisitionand analysis, modelization and simulations of the phenomenon, furthermore, to study the parameters influencing the effect, such as vacuum chamber material, cleaning, surface treatments, to better understand multipacting and determine the most effective ways to avoid this critical effect for the LHC accelerator. eng 2000
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2000-018; http://cds.cern.ch/record/444457/files/thesis-2000-018.pdf; http://cds.cern.ch/record/444457/files/thesis-2000-018.ps.gz;
Imported from Invenio. Le Pimpec, F Etude de la désorption moléculaire induite par transitions électroniques dans les surfaces techniques L'étude des particules créées lors des collisions protons-protons à 7 TeV, qui se produiront dans le Large Hadron Collider (LHC), permettra aux physiciens des hautes énergies de mieux comprendre la structure de la matière et de notre univers. Pour construire une telle machine, de nouvelles technologies vont devoir être développées. Ces technologies nécessitent de mieux comprendre les problèmes physiques qui se produiront dans l'accélérateur. Un des problèmes est de s'assurer de la durée de vie des faisceaux. Celle-ci est directement liée au nombre de molécules présentes dans les chambres à vide.. fre CERN Geneva 2000
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2000-017; http://cds.cern.ch/record/444304/files/thesis-2000-017.pdf;
Imported from Invenio. Flemsæter, Bjorn Investigation, modelling and control of the 1.9 K cooling loop for superconducting magnets for the Large Hadron Collider The temperature of the superconducting magnets for the 27 km LHC particle accelerator under construction at CERN is a control parameter with strict operating constraints imposed by (a) the maximum temperature at which the magnets can operate, (b) the cooling capacity of the cryogenic system, (c) the variability of applied heat loads and (d) the accuracy of the instrumentation. A pilot plant for studying aspects beyond single magnet testing has been constructed. This magnet test string is a 35-m full-scale model if the LHC and consists of four superconducting cryogmagnets operating in a static bath of He II at 1.9 K. An experimental investigation of the properties dynamic characteristics of the 1.9 K cooling loop of the magnet test string has been carried out. A first principle model of the system has been created. A series of experiments designed for system identification purposes have been carried out, and black box models of the system have been created on the basis on the recorded data. A Model Predictive Controller has been implemented for controlling the temperature of the 1.9 K level, using models obtained in the system identification. A temperature control with a narrower control band can in principle be achieved with an MPC-type controller than when using a PID controller. Experiments show that the controller has promising properties for tackling the dynamic challenges posed by the design of the 1.9 K cooling loop. Through the experimental investigation it has been found that: - the amount of pressurised He II in the cold mass is 180 kg - the thermal conductance of the heat exchanger tube is 74 W/Km - the velocity of the advancing liquid in the heat exchanger is in the order of 10 cm/s. The interaction between the gas and liquid phase is weak - longitudinal and transverse heat transfer capability is very high The system is found to be: - strongly non-linear primarily through He II and the density of the helium gas - non-minimum phase and exhibiting inverse response - open loop unstable, also denoted non self-regulating - containing variable transport delay The first principle model is capable of reproducing steady state and transient characteristics of the system. Of particular importance the pressure drop calculation in the heat exchanger is verified to be in good agreement with observed behaviour. Linear black box models are verified to satisfactory represent the system around the working point. Using linear models the performance of the MPC controller was found to be as good as or better than the classical PID control structure used up to date. Results indicate that improved performance will offset the increased initial cost and technical complexity of the control system and add to a robust and fault tolerant operation of the system. eng 1.9; CERN Geneva 2000
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2000-013; http://cds.cern.ch/record/433397/files/thesis-2000-013.pdf; http://cds.cern.ch/record/433397/files/thesis-2000-013.ps.gz;
Imported from Invenio. Herleb, U Neutralisation der Raumladung eines Aluminiumionenstrahls mit gepulsten Elektronenstrahlen ger Erlangen - Nuremberg U. Erlangen 1997
http://cds.cern.ch/record/401830/files/Thesis-1997-Herleb.pdf;
Imported from Invenio. Schneider, M Decay and snapback studies on the LHC dipole model magnets: a scaling law eng Wien TU Wien 1998
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=CM-P&id=CM-P00068841; http://cds.cern.ch/record/401684/files/CM-P00068841.pdf;
Imported from Invenio. Peón-Hernández, G Thermo-mechanical study and optimization of vertical vapour shielded cryostats for SMES applications: design of components for the main LHC cryostat eng CERN Geneva 1997
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=thesis-99-002; http://cds.cern.ch/record/387733/files/Thesis-1997-Peon-Hernandez.pdf;
Imported from Invenio. Riddone, G Theoretical Modeling and Experimental Investigation of the Thermal Performance of the LHC Prototype Lattice Cryostats This thesis presents the thermal performance of the LHC (Large Hadron Collider) prototype cryostats both in steady-state and in transient conditions. LHC will be built in the 27 km LEP tunnel and will provide proton-proton collisions. It will make use of superconducting magnets operating in static bath of superfluid helium at 1.9 K. The thesis is mainly divided in three parts. The first part cont ains three chapters which present a brief overview of the LHC project. Part 1-Chapter 1 gives a short introduction to the LHC design layout and performance. Part 1-Chapter 2 refers to LHC cryogenic s ystem and describes the general architecture of the cryogenic plants, the temperature levels and the heat loads. The 50 m long LHC prototype half-cell contains one twin-bore quadrupole and four twin-a perture dipoles. In Part 1-Chapter 3 the design and construction of the prototype dipole and quadrupole cryostats are presented. The LHC prototype cryostats have integrated cryogenic lines, while the final LHC cryostats have separate distribution lines. The second part of the thesis illustrates the steady-state cryostat thermal performance beginning with a short description of the heat transfer p rocesses involved in the cryostat thermal budget (Part 2-Chapter 1). An overview of material and helium properties is given in Annexes 2 and 3. The mathematical model used to simulate the cryostat the rmal performance has been validated and the experimental tools used to accomplish this aim are presented in Part 2-Chapter 2. Full-scale prototype cryostats have been designed, constructed and use to assess the cryogenic behaviour. The thermal performance of the cryostats has been investigated both in nominal and in degraded operating conditions and is presented in Part 2-Chapter 3. Screen tempera ture and residual gas pressure have been varied in order to investigate their influence on the total thermal budget. The heat load due to resistive heating in the non-superconducting cable splices h as been analysed and results form electrical measurements have been compared with those from calorimetric measurements. The list of detailed heat loads for the CTM and the string test is given in Anne x 1. The heat interceptions play a very important role in the cryostat thermal performance, since low heat inleaks can be maintained only with a very efficient thermalisation. The main components whic h need to be cooled at intermediate temperatures are the screens, the support posts, the cryogenic valves and the vacuum barrier. The thermal contacts between these components and the cooling pipes ha ve been studied in different cryostats and results of their thermal impedances are presented. Annex 4 describes the basic concept of thermal contacts and gives a few empirical correlations which may b e applied in specific cases. The last chapter in Part 2 presents the potential of an actively cooled "soft" screen with respect to the "floating" insulation system. The efficiency of a soft screen dep ends on the quality of the heat interception and the insulation to the cold mass. test set-ups have been constructed to measure the thermal impedance of shrink-fitted type thermal contacts a nd the conduction through net-type insulating spacers. Test set-up and measurements results are described. The third part explains the cryostat thermal performance in transient modes. Forced flow coo ldown and warmup have been tested in the LHC prototype magnet string and calculated and experimental results are exposed in Part 3-Chapter 1. Natural warmup with and without active pumping on the insu lation system is described in Part 3-Chapter 2 as well as the simulation of accidental loss of insulation vacuum. For each case a one-dimensional non-linear mathematical model has been developed and validated against measured data. eng CERN Geneva 1997
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=CM-P&id=CM-P00069602; http://cds.cern.ch/record/359357/files/CM-P00069602.pdf;
Imported from Invenio. Paul, C Numerical calculation of the saturation induced field errors in the main dipole of CERN's future Large Hadron Collider eng Graz TU Graz 1997
http://preprints.cern.ch/cgi-bin/setlink?base=preprint&categ=CM-P&id=CM-P00068802; http://cds.cern.ch/record/339467/files/CM-P00068802.pdf;
Imported from Invenio. Meineke, A Laserinduzierte Elektronenemission von Ferroelektrika ger Berlin TU Berlin 1995
http://cds.cern.ch/record/298116/files/Thesis-1995-Meineke.pdf;
Imported from Invenio. Schwerg, N Determination of a Fit Function for the Critical Current Density for NbTi Cables used in LHC Main Bending Magnets: Student Research Project For the construction of the LHC at CERN the main dipoles and the superconducting cables are produced in industry. As part of the quality control the field quality of the magnets is measured both at warm and at cold conditions at CERN. In superconducting accelerator magnets field errors are mainly created by the positioning of the conductors, but also by so-called persistent currents. These currents are linked to the superconductor magnetization and they are an inevitable property of type II superconducting materials. The superconductor magnetization behavior of each strand used for the LHC main dipoles is tested at CERN and the cable has to be approved before use. It has been observed that the dependency of the superconductor magnetization on the applied magnetic induction is different for the different manufacturers. Based on the magnetization measurements and the critical state model the persistent current effects can be calculated by means of a model for superconducting filaments. For this thesis the intersecting ellipse model is used which is implemented in the CERN field computation program ROXIE and is used for the calculation of the expected field errors in the LHC magnets. In this work a new fit function for the critical current density of NbTi cables for the LHC main dipoles is presented. This newly developed fit function is used as input for the existing sc model and complete magnet cross-sections have been calculated. The simulation results have been compared with measurements at cold of the LHC main dipoles. A very good agreement with measurements for small and intermediate field values could be observed. eng CERN Geneva 2005
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2005-020; http://cds.cern.ch/record/835157/files/thesis-2005-020.pdf;
Imported from Invenio. Völlinger, C Superconductor Magnetization Modeling for the Numerical Calculation of Field Errors in Accelerator Magnets Superconducting magnets are obligatory today in order to provide the high magnetic fields that are needed for the acceleration of heavy particles in particle accelerators. The coils of such magnets are made of type II superconducting material and are exposed to a changing magnetic field which induces a so-called persistent current. Persistent currents are bipolar screening currents that do not decay, but persist due to the lack of resistivity in the superconductor. This way, they are the source of a superconductor magnetization in the coil which disturbs the field quality in the magnet aperture. In the framework of this thesis, a macroscopic superconductor model for the calculation of the magnetization of a thin superconducting cylinder of type II material has been developed. The model considers the dependency of the induced current density on the applied field as well as the local distribution of the magnetic induction within the superconductor. Both, the one-dimensional case of a homogeneous change of an external field as well as the case of rotating magnetic inductions with arbitrary excercising angles in the plane are considered. The repercussion of the screening field on the applied field is considered by means of a fixed-point iteration. A relaxation method accelerates and stabilizes the convergence of the iteration. Hysteresis effects that occur in the superconductor in case of a change in the external field are fully re-produced. The model has been incorporated into the CERN field computation program ROXIE and in such a way is combined with numerical methods as the coupled method of finite elements and boundary elements. This way, the calculation of field errors resulting from non-linear materials as used in accelerator magnets, is possible in combination with the superconductor model. The model has been verified by comparing the calculated field errors with measurements for various magnet types, typically for use in particle accelerators, today. Different methods for compensating the persistent current effect are discussed and one method of inserting a ferromagnetic sheet has been tested and experimentally confirmed the predicted compensatory effect. eng CERN Geneva 2002
http://documents.cern.ch/cgi-bin/setlink?base=preprint&categ=cern&id=cern-thesis-2003-022; http://cds.cern.ch/record/633599/files/thesis-2003-022.pdf; http://cds.cern.ch/record/633599/files/thesis-2003-022.ps.gz;
Imported from Invenio.