Identification of Assembly Faults through the Detection of Magnetic Field Anomalies in the Production of the LHC Dipoles

Magnetic measurements at room temperature have been used to monitor the production of the superconducting coils of the Large Hadron Collider main dipoles. They have made it possible to identify several assembly errors, e.g. cases of bad gluing of the coil layers, bad conductor positioning, missing pole shims and other problems related to faulty procedures. This paper reviews the experience accumulated so far considering almost 1000 dipoles. After a short outline of the method used to pin out field anomalies and deduce realistic deformation of the coil, an exhaustive list of the cases met during the production is given. A discussion follows on the findings after decollaring as compared to the predictions, including the still open cases

Building the impedance model of a real machine

A reliable impedance model of a particle accelerator can be built by combining the beam coupling impedances of all the components. This is a necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an impedance reduction is required, and study the interaction with other mechanisms such as optics nonlinearities, transverse damper, noise, space charge, electron cloud, beam-beam (in a collider). The main phases to create a realistic impedance model, and verify it experimentally, will be reviewed, highlighting the main challenges. Some examples will be presented revealing the levels of precision of machine impedance models that have been achieved

A Study on New Trial Mode Regarding Real Estate Registration Civil-Administrative Interweaving Case

不动产登记案件中民事争议与行政争议交叉现象日渐显现，但目前我国法律尚未具体规定民事与行政交叉案件的审理办法，司法解释也未对此提出周详的解决方案，如何正确审理此类案件成为司法界一大难点问题。本文以实践中产生争议最大、问题最多的一类民行交叉案件——不动产登记纠纷为研究视角，在现有法律框架下，澄清实践中一些错误的观念和看法，提出并行诉讼模式，为解决当事人的民事、行政争议并使登记记载与事实归于一致提供了一种新鲜的模式。全文除引言和结语外，分为四章： 第一章从四个常见案例入手对不动产登记纠纷进行类型化研究，介绍了现行民事、行政交叉案件的五种常见的审理模式，并对这五种审理模式遭遇的困境进行反思。现有的五...The interweaving of civil and administrative disputes is becoming more and more apparent in real estate registration cases. To date, legislations in our country have specifically not dealt with how to hear civil and administrative interweaving cases, and judicial interpretations does not render detailed solutions either. As a result, how to correctly adjudicate such cases has become a difficulty f...学位：法律硕士院系专业：法学院法律系_法律硕士(JM)学号：X200712004

Enlargement of Tuning Range in a Ferrite-Tuned Cavity Through Superposed Orthogonal and Parallel Magnetic Bias

Conventional ferrite-tuned cavities operate either with bias fields that are orthogonal or parallel to the magnetic RF-field. For a cavity that tunes rapidly over an overall frequency range around 100-400 MHz with high Q, we use ferrite garnets exposed to an innovative new biasing method consisting of a superposition of perpendicular and parallel magnetic fields. This method leads to a significant enlargement of the high-Q cavity tuning range by defining an operation point close to the magnetic saturation and thus improving ferrite material behaviour. A further advantage of this technique is the fast tuning speed resulting from the fact that tuning is carried out either with pure parallel biasing, or together with a very small change of operating point from perpendicular bias. In this paper, several scaled test models of ferrite-filled resonators are shown; measurements on the set-ups are compared and discussed

Improved HOM-mitigation for future SPS 33-Cell 200 MHz traveling-wave accelerating structures

The CERN SPS 200 MHz traveling-wave (TW) accelerating structures pose an intensity limitation for the planned High Luminosity (HL-) LHC upgrade. Higher-order modes (HOMs) around 630 MHz have been identified as one of the main sources of longitudinal multi-bunch instabilities. Improved mitigation of these HOMs with respect to today’s HOM-damping scheme is therefore an essential part of the LHC injectors upgrade (LIU) project. The basic principles of HOM-couplers in cavities and today’s damping scheme are reviewed. Before illustrating the numerous requirements, an improved damping scheme for the future 33-cell structures must be fulfilled. These are, among others, the mitigation of HOMs situated in the lower part of the structure where there are no access ports for extraction, a sufficient overall damping performance and an acceptable influence on the fundamental accelerating passband (FPB). Different approaches tackling these challenges are investigated and their performance, advantages and pitfalls are evaluated by ACE3P and CST electromagnetic (EM) field solver suites

Studies for the SPS Travelling Wave Cavities Upgrade

The Super Proton Synchrotron\,(SPS) 200\,MHz accelerating system poses an intensity limitation for the planned High Luminosity\,(HL)-LHC upgrade due to excessive beam loading as well as higher-order modes\,(HOMs) contributing to a longitudinal multi-bunch instability. The mitigation of these HOMs together with a shortening of the cavities is therefore an essential part of the LHC Injectors Upgrade\,(LIU) project. A brief introduction to the accelerating structure as well as its present and future cavity configurations is given. First conclusions are drawn from lab measurements performed on three spare cavity sections regarding tuning and beam impedances. The following studies on longitudinal impedance are targeted towards the shorter cavity configuration used in the future. The particular difficulties inherent to the HOM-damping of this configuration are identified and illustrated. Taking these findings into account, a first improved HOM-damping scheme with regard to the scheme in use today is developed

A Large Aperture Superconducting Dipole for Beta Beams to Minimize Heat Deposition in the Coil

The aim of beta beams in a decay ring is to produce highly energetic pure electron neutrino and anti-neutrino beams coming from b-decay of 18Ne10+ and 6He2+ ion beams. The decay products, having different magnetic rigidities than the ion beam, are deviated inside the dipole. The aperture and the length of the magnet have to be optimized to avoid that the decay products hit the coil. The decay products are intercepted by absorber blocks inside the beam pipe between the dipoles to protect the following dipole. A first design of a 6T arc dipole using a cosine theta layout of the coil with an aperture of 80 mm fulfils the optics requirements. Heat deposition in the coil has been calculated using different absorber materials to find a solution to efficiently protect the coil. Aspects of impedance minimization for the case of having the absorbers inside the beam pipe have also been addressed

The Effect of 2-Directional Magnetic Biasing Used for Tuning of a Ferrite-Loaded Re-entrant Cavity

Cavities that are partially filled with ferrite material provide a tunable resonance frequency by making use of the changing μ-characteristics of ferrites when exposed to an external magnetic bias field. The concept of using either parallel or perpendicular magnetic biasing to reach a certain resonance frequency of a cavity has been known for many years. However, a cavity based on superposition of perpendicular and parallel magnetic fields to obtain improved ferrite characteristics was suggested in [1], but to our knowledge was neither tested nor built. Such a 2-directional biasing is expected to provide a reduction in RF losses for an identical tuning range as compared with the classical 1-directional magnetic bias. We have successfully tested this theory with a measurement set-up consisting of a ferrite-filled cavity, exposed to external biases that allow the clear separation of the two orientations of superposed magnetic bias fields. The outcome is an enlargement of tuning range with high cavity Q and the possibility of fast tuning. In this paper, we describe the measurement set-up and present the tuning ranges that we attained by applying different bias schemes

Permittivity and permeability measurements methods for particle accelerator related materials

For the special requirements related to particle accelerators, knowledge of the different material parameters of dielectrics and other materials are needed in order to carry out simulations during the design process of accelerator components. This includes also properties of magnetically biased ferrites of which usually little information is available about material characteristics, especially in magnetic bias fields. Several methods of measurement are discussed and compared of which some require delicate sample preparation whereas others can work with unmodified material shapes that makes those methods also suited for acceptance checks on incoming materials delivered by industry. Applications include characterization of different materials, as absorbers in which dielectric losses play an increasing role, as well as low frequency measurements on ferrites that are used for tunable cavities. We present results obtained from both broadband and resonant measurements on different materials determined in the same sample holder. Where possible, the results were confirmed with alternative methods