Evaluation of Impact from Ripple and Transient Phenomena in the LHC Dipole Strings

Based on measurements of the A.C. electrical characteristics of prototype magnets, synthesized computer models of the principal, individual, superconducting magnetic elements of the Large Hadron Collider have been elaborated. The models constitute the basic elements for the determination of the transfer functions of the magnet chains. This tool provides the possibility to evaluate the resonance spectrum of the chains and to determine the needs for additional damping. Results of the analysis of transmission line effects in the LHC main dipole chains are presented. In particular, data from ripple calculations and ramping studies are discussed. Computer simulations of the quench protection circuit provide information about the transient phenomena occurring in the dipole chains during normal operation of the fast de-excitation switches and under abnormal conditions

Energy Extraction for the LHC Superconducting Circuits

The superconducting magnets of the LHC will be powered in about 1700 electrical circuits. The energy stored in circuits, up to 1.3 GJ, can potentially cause severe damage of magnets, bus bars and current leads. In order to protect the superconducting elements after a resistive transition, the energy is dissipated into a dump resistor installed in series with the magnet chain that is switched into the circuit by opening current breakers. Experiments and simulation studies have been performed to identify the LHC circuits that need energy extraction. The required values of the extraction resistors have been computed. The outcome of the experimental results and the simulation studies are presented and the design of the different energy extraction systems that operate at 600 A and at 13 kA is described

The Protection System for the Superconducting Elements of the Large Hadron Collider at CERN

The protection system for the superconducting elements of the Large Hadron Collider (LHC) [1] at the European Laboratory for Particle Physics (CERN), and its associated equipment are presented: quench detectors, cold diodes, quench heaters and related power supplies, extraction resistors and associated current breakers. Features such as radiation resistance, redundancy and required reliability are discussed

Direct observation of the Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed matter physics. The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu$-$Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics, is prone to decay into a pair of low-energy Nambu$-$Goldstone modes in low dimensions. Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using the inelastic neutron scattering and applying the bond-operator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S=1/2 quantum antiferromagnet C$_9$H$_{18}$N$_2$CuBr$_4$ near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.Comment: 12 pages, 4 figures in the main text+3 figures in Supplementary Informatio

First Powering of the LHC Test String 2

String 2 is a full-size model of a regular cell in an LHC arc. In the first phase, three dipole magnets and two quadrupole magnets have been assembled in String 2 and commissioning started in April 2001. By the beginning of 2002 three pre-series dipole magnets will be added to complete the cell. As for its predecessor String 1, the facility was built to individually validate the LHC systems and to investigate their collective behaviour for normal operation with the magnets at a temperature of 1.9 K, during transients as well as during exceptional conditions. String 2 is a precious milestone before installation and commissioning of the first LHC sector (1/8 of the machine) in 2004, with respect to infrastructure, installation, tooling and assembly procedures, testing and commissioning of individual systems, as well as the global commissioning of the technical systems. This paper describes the commissioning, and retraces the first powering history

Experiments and cycling at the LHC prototype helf-cell

The first version of the LHC prototype half-cell has been in operation since February 1995. It consists of one quadrupole and three 10-m twin aperture dipole magnets which operate at 1.8 K. This experimental set-up has been used to observe and study phenomena which appear when the systems are assembled in one unit and influence one another. The 18-month long experimental program has validated the cryogenic system and yielded a number of results on cryogenic instrumentation, magnet protection and vacuum in particular under non-standard operating conditions. The program was recently complemented by the cycling experiment: it consisted in powering the magnets following the ramp rates which will be experienced by the magnets during an LHC acceleration. In order to simulate 10 years of routine operation of LHC, more than 2000 1-hour cycles were performed interleaved with provoked quenches. The objective of this experiment was to reveal eventual flaws in the design of components. The prototype half-cell performed to expectations showing no sign of failure of fatigue of components for more than 2000 cycles until one of the dipoles started exhibiting an erratic quench behavior

Trajectories of depression in sepsis survivors: an observational cohort study

Background: Advances in critical care medicine have led to a growing number of critical illness survivors. A considerable part of them suffers from long-term sequelae, also known as post-intensive care syndrome. Among these, depressive symptoms are frequently observed. Depressive symptom trajectories and associated factors of critical illness survivors have rarely been investigated. Study objective was to explore and compare different trajectories of depressive symptoms in sepsis survivors over 1 year after discharge from ICU. Methods: Data of a randomized controlled trial on long-term post-sepsis care were analyzed post hoc. Depressive symptoms were collected at 1, 6 and 12 months post-ICU discharge using the Major Depression Inventory (MDI), among others. Statistical analyses comprised descriptive analysis, univariate and multivariate, linear and logistic regression models and Growth Mixture Modeling. Results: A total of 224 patients were included into this analysis. We identified three latent classes of depressive symptom trajectories: Over the course of 1 year, 152 patients recovered from mild symptoms, 27 patients showed severe persistent symptoms, and 45 patients recovered from severe symptoms. MDI sum scores significantly differed between the three classes of depressive symptom trajectories at 1 and 6 months after ICU discharge (p = 35 on the Posttraumatic Stress Scale 10 vs. 48.1%/33.3%, p < 0.003); and higher levels of health-related quality of life (HRQOL) using the Short Form-36 scale within 1 month after ICU discharge (p < 0.035). Conclusions: In the first year after discharge from ICU, sepsis survivors showed three different trajectories of depressive symptoms. Course and severity of depressive symptoms were associated with chronic pain, posttraumatic stress and reduced HRQOL at discharge from ICU. Regular screening of sepsis survivors on symptoms of depression, chronic pain and posttraumatic stress within 1 year after ICU may be considered