Design and Performance Optimization of the LHC Collimation System

The Large Hadron Collider (LHC) is presently under construction at CERN. The LHC is a circular accelerator that stores proton beams and accelerates them to a 7 TeV beam energy. The required bending fields are achieved with super-conducting magnets. The stored proton beams are collided in experimental detectors and produce a design luminosity of 1E+34 cm-2.s-1. Every storage ring encounters unavoidable proton losses. The protons that diffuse into the so-called beam halo can touch accelerator components. In order to avoid quenches of the superconducting magnets, the halo protons must be removed before reaching the magnets. This is achieved with a multi-stage cleaning system, built out of two-sided collimators that are located at adequate positions in the machine. Due to the high stored beam intensity (required for high luminosity), the efficiency of the LHC beam cleaning must be much better than in any other exisiting machine: not more than 0.00002% of protons hitting the collimators may escape and impact on any meter of super-conducting magnet at 7 TeV. Detailed simulations of realistic operational conditions were performed to address the performance of the cleaning system. Beam loss maps show the distribution of proton losses around the machine down to the 10 cm level. The simulations were used for optimizing the system design and improving its overall efficiency by more than a factor of 10. The final performance of the so-called "phase 1" collimation system is discussed for the ideal LHC machine and for a case with a realistically perturbed orbit. For the phase 1 system, it is predicted that the allowable LHC intensity is limited to 43% (ideal case) or 27% (nominal orbit) of the nominal design value. The limitations and the assumptions used to derive theses limits are explained, including a list of characteristic loss locations around the ring. A prototype LHC collimator was tested in the SPS with LHC-like proton beam conditions (injection energy). The control and beam-based alignment of the collimator gap was demonstrated down to the 50 um level. Interesting results on the beam dynamics for halo particles were obtained, including slowly decaying beam losses after movement of collimator jaws. The robustness of the CFC (fiber-reinforced graphite) collimator jaws was experimentally confirmed and results were compared with predictions from numerical models

Design and Performance Optimization of the LHC Collimation System (CERN-THESIS-2006-069)

The Large Hadron Collider (LHC) is presently under construction at CERN. The LHC is a circular accelerator that stores proton beams and accelerates them to a 7 TeV beam energy. The required bending fields are achieved with super-conducting magnets. The stored proton beams are collided in experimental detectors and produce a design luminosity of 1034 cmâ2sâ1. Every storage ring encounters unavoidable proton losses. The protons that diffuse into the so-called beam halo can touch accelerator components. In order to avoid quenches of the superconducting magnets, the halo protons must be removed before reaching the magnets. This is achieved with a multi-stage cleaning system, built out of two-sided collimators that are located at adequate positions in the machine. Due to the high stored beam intensity (required for high luminosity), the efficiency of the LHC beam cleaning must be much better than in any other exisiting machine: not more than 0.00002 % of protons hitting the collimators may escape and impact on any meter of super-conducting magnet at 7 TeV. Detailed simulations of realistic operational conditions were performed to address the performance of the cleaning system. Beam loss maps show the distribution of proton losses around the machine down to the 10 cm level. The simulations were used for optimizing the system design and improving its overall efficiency by more than a factor of 10. The final performance of the so-called âphase 1â collimation system is discussed for the ideal LHC machine and for a case with a realistically perturbed orbit. For the phase 1 system, it is predicted that the allowable LHC intensity is limited to 43 % (ideal case) or 27 % (nominal orbit) of the nominal design value. The limitations and the assumptions used to derive theses limits are explained, including a list of characteristic loss locations around the ring. A prototype LHC collimator was tested in the SPS with LHC-like proton beam conditions (injection energy). The control and beam-based alignment of the collimator gap was demonstrated down to the 50 μm level. Interesting results on the beam dynamics for halo particles were obtained, including slowly decaying beam losses after movement of collimator jaws. The robustness of the CFC (fiber-reinforced graphite) collimator jaws was experimentally confirmed and results were compared with predictions from numerical models

Loss maps of RHIC

State-of-the-art tracking tools were recently developed at CERN to study the cleaning efficiency of the Large Hadron Collider (LHC) collimation system . These tools are fully transportable, meaning that any accelerator lattice that includes a collimation systemcan be simulated. Each of the two Relativistic Heavy Ion Collider (RHIC) beam lines features a multi-stage collimation system, therefore dedicated datasets from RHIC operations with proton beams can be used to benchmark the tracking codes and assess the accuracy of the predicted hot spots along the LHC

Comparison between measured and simulated beam loss patterns in the CERN SPS

A prototype of an LHC collimator has been tested with proton beams at the CERN SPS. The interaction of the circulating proton beam with the carbon collimator jaws generated secondary proton beams that were lost in the downstream SPS aperture. The measured beam loss patterns are compared with the results of dedicated loss simulations. The simulation package includes (1) a 6D particle tracking through the SPS lattice; (2) the scattering interaction of protons with the collimator jaw material; (3) the timedependent displacement of the collimator jaws with respect to the beam orbit; (4) a detailed aperture model of the full SPS ring. It is shown that the simulation tools can reliably predict the measured location of losses. This provides an important assessment of the simulation tools in view of the beam loss studies for the Large Hadron Collider (LHC)

Tertiary halo and tertiary background in the low luminosity experimental insertion IR8 of the LHC

In our report we present the results for numerical simulation of tertiary halo and tertiary background in the LHC. We study the case of the proton losses in the betatron cleaning insertion IR7 with the subsequent tertiary halo generation in the downstream experimental insertion IR8. We analyze the formation of tertiary background in the experimental area of the IR8 and evaluate the performance of the machine-detector interface shielding with respect to this source of the background. The results obtained are compared with the previous estimates of the machine-induced background in the low luminosity insertions of the LHC, and the balance between different sources of the background is discussed

LHC collimation efficiency during commissioning

The design of the LHC collimation system requires understanding and maximizing the ultimate performance with all collimators. However, for the commissioning of the LHC it is important to analyze the collimation efficiency with certain subsets of collimators, with increased collimator gaps and relaxed set-up tolerances. Special studies on halo tracking and energy deposition have been performed in order to address this question. The expected cleaning performance and intensity limits are discussed for various collimation scenarios which might be used during commissioning of the LHC

Beam Halo on the LHC TCDQ Diluter System and Thermal Load on the Downstream Superconducting Magnets

The moveable single-jawed graphite TCDQ diluter must be positioned very close to the circulating LHC beam in order to prevent damage to downstream components in the event of an unsynchronised beam abort. A two-jawed graphite TCS.IR6 collimator forms part of the TCDQ system. The requirement to place the jaws close to the beam means that the system can intercept a substantial beam halo load. Initial investigations indicated a worryingly high heat load on the Q4 coils. This paper presents the updated load cases, shielding and simulation geometry, and the results of simulations of the energy deposition in the TCDQ system and in the downstream superconducting Q4 magnet. The implications for the operation of the LHC are discussed

Study on Probationary System

缓刑制度是现代刑事政策的一项重要内容，也是世界各国普遍采用的一项行刑制度。它具有避免短期自由刑的弊端、帮助犯罪人再社会化和节约国家的经济支出等多项优点，在一般预防和特殊预防两方面都发挥了重要作用。作为一种人道主义的行刑方式，缓刑符合行刑经济性、轻刑化和社会化的原则，挽救了大批的犯罪人。由于受重刑传统的影响，我国的缓刑制度尚存在立法和司法上的缺陷，这些缺陷大大削弱了缓刑价值。因此，我国的缓刑制度亟待完善。 本文对中外缓刑制度进行了比较研究，并以此为基础，指出中国现行缓刑制度的弊端，同时结合中国的实际国情，着重对缓刑制度的根据进行了梳理和总结，并对在司法理论和实践中出现的种种问题进行深入地思考与...The probationary system, an important part of modern criminal polices and a popular system of execution adopted worldwide, is helpful in overcoming disadvantages of short-term punishment against liberty, saving governments' spending and in criminals’ resocialization. At the same time, it plays a significant role both in general prevention and in special prevention. As a form of execution out of hu...学位：法律硕士院系专业：法学院法律系_法律硕士(JM)学号：X20030818