Accurate calculation of fringe fields in the LHC main dipoles

The ROXIE program developed at CERN for the design and optimization of the superconducting LHC magnets has been recently extended in a collaboration with the University of Stuttgart, Germany, with a field computation method based on the coupling between the boundary element (BEM) and the finite element (FEM) technique. This avoids the meshing of the coils and the air regions, and avoids the artificial far field boundary conditions. The method is therefore specially suited for the accurate calculation of fields in the superconducting magnets in which the field is dominated by the coil. We will present the fringe field calculations in both 2d and 3d geometries to evaluate the effect of connections and the cryostat on the field quality and the flux density to which auxiliary bus-bars are exposed     

Production follow-up of the LHC main dipoles through magnetic measurements at room temperature

In this paper, we review the tools used for controlling the production of the LHC main dipoles through warm magnetic measurements. For the collared coil measurements, control limits are based on the statistics relative to the pre-series production. For the cold mass, the difference between collared coil and cold mass is considered, allowing a very stringent test. In both cases, measurements are split in straight part average, variations and coil ends contributions. Two different alarm levels exist in case the measured field is out of limits. The analysis can be carried out at the manufacturer and allows detection of anomalies in the measured magnetic field. These can be either due to wrong measurements or caused by assembly defects. Techniques used to work out information on the magnet assembly from the field harmonics are outlined. We summarize the experience gathered on about 180 collared coils and 120 cold masses, pointing out the bad cases and investigating the reliability of the measurements.     

Shape analysis of the LHC pre-series dipoles

This paper presents the results of a comprehensive analysis, from the geometric point of view, of the pre-series LHC dipoles. The progressive change of the imposed magnet shape has been monitored from the first assembly stage until after the cold test. Data concerning the error on sagitta, extremity positions and sextupolar corrector positions are provided for the pre-series magnets. Implications of aligning out-of-tolerance dipoles by the extremities are also discussed.     

Correlations between field quality and geometry of components in the collared coils of the LHC main dipoles

The Large Hadron Collider (LHC) (1995), a proton-proton superconducting accelerator, will consist of about 8400 superconducting magnet units, all operating in superfluid helium at a temperature of 1.9 K. The design of the superconducting main dipole magnets for the LHC is guided by the requirement of an extremely high field quality in the magnet aperture which is mainly defined by the layout of the superconducting coil and the position of the conductors. In order to avoid conductor movements within the magnet cross-section, the superconducting coils are held in place by surrounding stainless steel collars. In this paper, we review the dependence of field harmonics in the LHC main dipoles on dimensions of the hardware components of the collared coils. An analysis of the dimensional measurements of these components which are used in the collared coils produced so far is given. Sensitivity tables which are worked out through a coupled magneto-static model give the variation of the multipoles on collars, copper wedge dimensions and cable geometry. A Monte Carlo method is used to simulate the effects of possible errors on the multipoles.     

Quench performance and field quality of the LHC preseries superconducting dipoles

The preseries production of the LHC main superconducting dipoles is presently being tested at CERN. The foremost features of these magnets are: twin structure, six block two layer coils wound from 15.1 mm wide graded NbTi cables, 56 mm aperture, polyimide insulation and stainless steel collars. The paper reviews the main test results of magnets tested to day in both normal and superfluid helium. The results of training performance, magnet protection, electrical integrity and the field quality are presented in terms of the specifications and expected performance of these magnets in the future accelerator.     

Loss and dynamic magnetic field measurements in LHC dipoles

Knowledge of AC loss and dynamic magnetic field distortion in the main LHC dipoles is both important for the assessment of the accelerator performance and providing insight into the properties of assembled magnets. We measured the loss due to the current cycling in a few 1-meter long model dipoles, 15-meter long dipole prototypes and pre-series magnets. As expected the loss depends linearly on the rate of the current change. From the slope of this dependence, the contact resistance between the strands of the opposite layers of the cable, R/sub c/, was evaluated for the inner winding of the dipole. We discuss the method to estimate the R/sub c/ value in the outer winding. The R/sub c/ value has been also derived independently from measurements of the magnetic field. For this, the ramp rate dependent component of the main field as well as of the harmonics has been measured. The main magnetic field measurements were performed using both stationary coils and Hall probes. Rotating coils were used to perform the harmonic measurements.     

Superconducting magnets for the LHC main lattice

The main lattice of the Large Hadron Collider (LHC) employs about 1600 main magnets and more than 4000 corrector magnets. All superconducting and working in pressurized superfluid helium bath, these impressive line of magnets fills more than 20 km of the underground tunnel. With almost 70 main dipoles already delivered and 10 main quadrupoles almost completed, we passed the 5% of the production and now all manufacturers have fully entered into series production. In this paper the most critical issues encountered in the ramping up in such a real large scale fabrication is addressed; uniformity of the coil size and of prestress, special welding technique, tolerances on curvature (dipoles) or straightness (quadrupoles) and of the cold mass extremities, harmonic content and, most important, the integrated field uniformity among magnets. The actual limits and the solution for improvements are discussed. Finally a realistic schedule based on actual achievements is presented.     

Selection of the cross-section design for the LHC main dipole

With the aim of selecting the most suitable design for the series production of the LHC main dipoles, several possible configurations were analysed with respect to admissible component tolerances and structural stability, field level, field quality, number and weight of parts. Two alternatives designs, featuring common collars made out of aluminium alloy and austenitic steel, respectively, were finally compared in detail, Although both designs are almost equivalent at nominal conditions, the austenitic steel collar structure turned out to be far less sensitive to components dimensional variations. This paper reports the main results of the above evaluations, which lead to the choice of austenitic steel collars for the LHC main dipoles     

Deformations and displacements of the LHC superconducting dipoles induced by standard and nonstandard operational modes

A full-scale and fully-instrumented working model of the LHC lattice cell has been tested at CERN between March and December 2002. Aside of the current, pressure and temperature sensors controlled by an industrial supervision system, a novel device has been set to monitor magnet positions with respect to the surrounding cryostat. The series of operating modes to test cryogenics, current leads and quench recovery electronics offered the chance to investigate potentially harmful deformations of the superconducting structure. In this paper, we present a survey of displacements and deformations experienced by the LHC cell magnets during thermal cycles, current ramps and resistive transitions. Although the system complexity prevented from complete modeling, a preliminary phenomena explanation is given.     

Statistical studies of the robustness of the LHC main dipolemechanical structure

This paper describes two methods used to study the effect of the tolerances of the components on the structure of the LHC main dipole. The first method, called semi-statistical, is useful for the determination of the acceptable variance of the dimensions of magnet components. The second one, fully statistical, allows the study of the combined effect of many parameters. The use of these two methods allowed to evaluate with good confidence the robustness of two different dipole cross-section designs, featuring austenitic and aluminium alloy collars, respectively     

Stress analysis of 3-dimensional IC package as function of structural design parameters

Solid Liquid Inter-Diffusion (SLID) is a technology that has recently been utilized to fabricate 3D ICs. Since application of this technology is in its infancy stages, manufacturability and reliability of these bonds are still under heavy investigations. This study presents an elastic-plastic finite element and analytical analyses that were implemented to evaluate effect of package design parameters on thermo-mechanical reliability of the SLID bonds and copper interconnects. A numerical experiment is designed in which several design parameters; die thickness, bond size, underfill stiffness and substrate thickness, are varied in 3 levels. Stress in SLID bonds and in copper interconnects were evaluated using the 3-dimensional finite element analysis as well as an analytical approach. The results show that die and substrate thicknesses are the most influential factors among the selected parameters on stress at the interface and on copper interconnects. Main effect results for stress analysis in SLID bonds using finite element shows that die thickness and underfill stiffness are the most influential factors in defining stress at SLID bonds. Results of the analytical approach confirm the finite element analysis. It is shown that effect of interconnect size and pitch is very small compared to die thickness. In average increasing die thickness increases both shear and peeling stresses at the interfaces and copper interconnects.     

Industrialization of LHC main quadrupole cold masses up to series production

Whereas the prototypes of the main quadrupoles had been pursued at CEA Saclay under contract with CERN, the contract to build all MQ magnets and the complete cold masses had been placed with ACCEL Instruments GmbH. After careful evaluation of design concepts and fabrication processes some revisions have been introduced to ease an industrial fabrication of the 400 MQ magnets and cold masses to be delivered to CERN. First batches of magnets were successfully cold tested. We report about the upgrading of the fabrication facility including the MQ specific layout of all machinery, the upgrading and qualifying of personnel resources and processes, the technical performance of the products and main activities and experiences on the way to series production.     

Measurement and analysis of axial end forces in a full-lengthprototype of LHC main dipole magnets

A full-length, twin aperture prototype (MBP2N1) dipole magnet for the LHC project was assembled at CERN with collared coils delivered by industry. The design of this prototype is close to that foreseen for the dipole series manufacture as far the coil geometry and that of the yoke components are concerned. The bolts that transfer the axial magnetic forces from the coil ends to the cold mass end plates were instrumented to verify the axial coil support. These axial forces were initially measured after partial assembly, during a standard and an accelerated cool down introduction to 1.9 K, and during magnet excitation up to 9.2 T. High force levels were observed, triggering a comparison with analytical models and measurements routinely made on 1-m single aperture dipole models. The prototype magnet was re-assembled with lower initial axial force settings and with additional instrumentation, to monitor these forces during the entire assembly process, and re-tested, to possibly correlate axial forces with training behaviour. This paper reports about the experimental observation and provides models towards their understanding     

The Interconnections of the LHC Cryomagnets at CERN: Strategy Applied and First Results of the Industrialization Process

The final interconnections of the LHC superconducting magnets in the underground tunnel are performed by a contractor on a result-oriented basis. A consortium of firms was awarded the contract after competitive tendering based on a technical and commercial specification. The implementation of the specific technologies and tooling developed and qualified by CERN has required an important effort to transfer the know-how and implement the follow-up of the contractor. This paper summarizes the start-up phase and the difficulties encountered. The organization and management tools put in place during the ramping-up phase are presented. In addition to contractual adaptations of the workforce, several configuration changes to the workflows were necessary to reach production rates compatible with the overall schedule and with the different constraints: availability of magnets, co-activities with magnets transport and alignment, handling of non-conformities, etc. Also the QA procedures underwent many changes to reach the high level of quality mandatory to ensure the LHC performance. The specificities of this worksite are underlined and first figures of merit of the learning process are presented.     

三维大区域电子沙盘实现技术研究

建立电子沙盘的关键在于如何真实地表现大区域地形地貌特征和如何在三维虚拟大场景中进行实时标绘。给出了基于CTS/Creator/Vega Prime的解决方案和软件的系统开发结构,并深入研究了实现电子沙盘的关键技术:利用CTS生成真实地形、利用VSG生成动态模型、基于碰撞检测的地表坐标获取和利用OpenGL在Vega Prime中显示汉字。最后结合研发实例阐述了电子沙盘的态势编辑、态势保存、场景浏览、地形分析、显示模式选择、图像输出等主要功能。     

Architecture level optimization of 3-dimensional tree-based FPGA

We describe a methodology to design and optimize Three-dimensional (3D) Tree-based FPGA by introducing a break-point at particular tree level interconnect to optimize the speed, area, and power consumption. The ability of the design flow to decide a horizontal or vertical network break-point based on design specifications is a defining feature of our design methodology. The vertical partitioning is organized in such a way to balance the placement of logic blocks and switch blocks into multiple tiers while the horizontal partitioning optimizes the interconnect delay by segregating the logic blocks and programmable interconnect resources into multiple tiers to build a 3D stacked Tree-based FPGA. We finally evaluate the effect of Look-Up-Table (LUT) size, cluster size, speed, area and power consumption of the proposed 3D Tree-based FPGA using our home grown experimental flow and show that the horizontal partitioned 3D stacked Tree-based FPGA with LUT and cluster sizes equal to 4 has the best area-delay product to design and manufacture 3D Tree-based FPGA.     

Radiation properties of microstrip dipoles

The fundamental problem of printed antennas is addressed. The printed or microstrip dipole is considered, and its radiation characteristics are investigated. The Green's function to the problem is obtained in dyadic form by solving the problem of a Hertzian dipole printed on a grounded substrate. Input impedance computations are presented, and the numerical solution for the Sommerfeld integrals is discussed.