Operational results with fast automatic beam-based LHC collimator alignment

The CERN Large Hadron Collider (LHC) is the largest and highest-energy particle accelerator ever built. It is designed to collide particles at a centre-of-mass energy of 14 TeV to explore the fundamental forces and constituents of matter. Due to the potentially destructive high-energy particle beams, with a total design energy of 362 MJ, the collider is equipped with a series of machine protection systems. The beam cleaning or collimation system is designed to passively intercept and absorb particles at large amplitudes. The cleaning efficiency depends heavily on the accurate positioning of the jaws with respect to the beam trajectory. Beam-based collimator alignment is currently the only feasible technique that can be used to determine the beam centre and beam size at the collimator locations. If the alignment is performed without any automation, it can require up to 30 hours to complete for all collimators. This reduces the beam time available for physics experiments. This article provides a brief recap of the algorithms and software developed to automate and speed up the alignment procedure, and presents the operational results achieved with fast automatic beam-based alignment in the 2011-2013 LHC runs.peer-reviewe

Self-calibration technique for characterization of integrated THz waveguides

Emerging high-frequency accelerator technology in the terahertz regime is promising for the development of compact high-brightness accelerators and high resolution-power beam diagnostics. One resounding challenge when scaling to higher frequencies and to smaller structures is the proportional scaling of tolerances which can hinder the overall performance of the structure. Consequently, characterizing these structures is essential for nominal operation. Here, we present a novel and simple self-calibration technique to characterize the dispersion relation of integrated hollow THz-waveguides. The developed model is verified in simulation by extracting dispersion characteristics of a standard waveguide a priori known by theory. The extracted phase velocity does not deviate from the true value by more than $9 \times 10^{-5} ~\%$. In experiments the method demonstrates its ability to measure dispersion characteristics of non-standard waveguides embedded with their couplers with an accuracy below $\approx 0.5~\%$ and precision of $\approx 0.05~\%$. Equipped with dielectric lining the metallic waveguides act as slow wave structures, and the dispersion curves are compared without and with dielectric. A phase synchronous mode, suitable for transverse deflection, is found at $275~\text{GHz}$.Comment: to be submitted to $\textit{Physical Review Accelerators and Beams}

Critical halo loss locations in the LHC

Results of simulations with all movable elements of the LHC collimation system [1] are discussed for various operation modes. Compared to previous results, the placing of additional collimators reduced the beam losses by a factor 10 in the ideal machine case, i.e. nominal collimators settings for both 450 GeV and 7 TeV beam energies. First results for Beam 2 are also reviewed. The sensitivity of the system to free orbit oscillations is addressed. These results show that it is sufficient to use a limited number of beam loss monitors (BLMs) for the setup and optimization of the LHC Collimation System

Semi-automatic beam-based alignment algorithm for the LHC collimation system

Full beam-based alignment of the LHC collimation system was a lengthy procedure as the collimators were setup manually. A yearly alignment campaign has been sufficient for now, although in future this may lead to a decrease in the cleaning efficiency if machine parameters such as the beam orbit drift over time. Automating the collimator setup procedure can allow for more frequent alignments, therefore reducing this risk. This paper describes the design and testing of a semi-automatic algorithm as a first step towards a fully automatic setup. Its implementation in the collimator control software and future plans are described.peer-reviewe

A Concept for the LHC Luminosity Upgrade Based on Strong Beta* Reduction combined with a Minimized Geometric Luminosity Loss Factor

A significant reduction of b* requires a new beam crossing scheme to overcome the consequence of the luminosity loss factor. We define in this paper the parameters of a possible solution taking advantage of an early separation scheme optionally supplemented by a weak crab crossing. Large aperture (150 mm) Nb$_{3}$Sn triplet quadrupoles are chosen for their compactness, temperature margin and ability to relax the collimator gap and impedance. This concept offers high performance for a moderate increase of complexity. An open issue is the possibility of integrating dipoles inside the detectors

An alternative nonlinear collimation system for the LHC

The optics design of an alternative nonlinear collimation system for the LHC is presented. We discuss an optics scheme based on a single spoiler located in between a pair of skew sextupoles for betatron collimation. The nonlinear system allows opening up the collimator gaps, thereby, reduces the collimator impedance, which presently limits the LHC intensity. After placing secondary collimators at locations behind the spoiler, we analyze the beam losses and calculate the cleaning efficiency from tracking studies. The results are compared with those of the conventional linear collimation system

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

Classification of LHC beam loss spikes using support vector machines

The CERN Large Hadron Collider's (LHC) collimation system is the most complex beam cleaning system ever designed. It requires frequent setups to determine the beam centres and beam sizes at the 86 collimator positions. A collimator jaw is aligned to the beam halo when a clear beam loss spike is detected on a Beam Loss Monitor (BLM) downstream of the collimator. This paper presents a technique for identifying such clear loss spikes with the aid of Support Vector Machines. The training data was gathered from setups held during the first three months of the 2011 LHC run, and the model was tested with data from a machine development period.peer-reviewe