Collimation for the LHC high intensity beams

The unprecedented design intensities of the LHC require several important advances in beam collimation. With its more than 100 collimators, acting on various planes and beams, the LHC collimation system is the biggest and most performing such system ever designed and constructed. The solution for LHC collimation is explained, the technical components are introduced and the initial performance is presented. Residual beam leakage from the system is analysed. Measurements and simulations are presented which show that collimation efficiencies of better than 99.97 % have been measured with the 3.5 TeV proton beams of the LHC, in excellent agreement with expectations.peer-reviewe

Challenges for Mobile Hydrostatic Levelling Systems applied in accelerator environments

The research for automated measurement solutions for the Large Hadron Collider (LHC) is a key point for future developments and of extreme importance for even bigger accelerators like the Future Circular Collider (FCC) where manual measurements are almost excluded due to the very large scale of the future machine. The developments for transversal measurements using close- range photogrammetry are making good progress and first results should be available from the High-Luminosity IT- String test in 2024 where a High Luminosity-LHC Triplet section will be fully tested on the surface. The R&D for the vertical measurements is still at the beginning and will combine close-range photogrammetry with mobile Hydro- static Levelling System (mHLS) measurements. HLS are commonly used in the field of high precision measurements or long-term monitoring of vertical displacements. The basic principle is quite robust and directly linked to an equipotential surface. There are several working principles available ranging from tactile, capacitive, or optical sensors to ultrasonic sensors in different configurations. For a mobile application, a particularly suitable system is the ultrasonic system with the transducer submerged in the water. A small number of critical aspects need to be solved to be usable in the Large Hadron Collider environment. The tunnel slope and system stabilization, the temperature gradient and atmospheric pressure differences due to tunnel ventilation needed to be considered in the design of the mobile system. The final goal is to make the system available for a use on a future Survey Train in the LHC. This paper describes the principle of the system along with some specific mitigation measures and validations for the mobile application

Measurement and alignment of the TIDVG5 SPS beam dump

During the Long Shutdown 2 (LS2 2018-2021) the CERN injector complex was upgraded to meet the future High Luminosity-Large Hadron Collider (HL-LHC) re- quirements. One major activity was the construction and installation of a new beam dump, in the Super Proton Synchrotron (SPS), able to cope with the increasing brightness of the high luminosity beams. The challenge for survey engineers was to align the beam dump and especially the core of the component within the tolerance required by the physicists. The measuring system had to ensure a transverse align- ment tolerance of ±0.7 mm (3σ) with respect to the beam axis defined by the surrounding quadrupoles, while facing many external constraints. A 2 m thick wall, composed of steel, concrete and marble, shields the new beam dump. The estimated dose for a year of operation is 1 MGy at 35 cm from the core. In addition, a bakeout of the dump up to 150°C is required to ensure the needed vacuum quality. The system had to be reliable and failsafe as there is no manual access possible during the 20 years of service. These heavy constraints led to a complete study of the spatial measure- ment system for the equipment. The paper describes in detail the design of the measure- ment and alignment system from the initial idea to the pro- totypes and the production. It also provides an overview of the tests and the first measurement results achieved

Managing the Survey Activities during LS1

The survey and alignment section has realised a huge campaign of measurements and re-alignment of accelerators and detectors components for the LHC and injectors complex. The permanent monitoring system around the triplets was also strongly upgraded and maintained. This paper describes the motivations for this campaign, the strategy to realise it from the technical and the manpower point of view as well as the first results

Dorsal premotor cortex exerts state-dependent causal influences on activity in contralateral primary motor and dorsal premotor cortex

During voluntary action, dorsal premotor cortex (PMd) may exert influences on motor regions in both hemispheres, but such interregional interactions are not well understood. We used transcranial magnetic stimulation (TMS) concurrently with event-related functional magnetic resonance imaging to study such interactions directly. We tested whether causal influences from left PMd upon contralateral (right) motor areas depend on the current state of the motor system, involving regions engaged in a current task. We applied short bursts (360 ms) of high- or low-intensity TMS to left PMd during single isometric left-hand grips or during rest. TMS to left PMd affected activity in contralateral right PMd and primary motor cortex (M1) in a state-dependent manner. During active left-hand grip, high (vs. low)-intensity TMS led to activity increases in contralateral right PMd and M1, whereas activity decreases there due to TMS were observed during no-grip rest. Analyses of condition-dependent functional coupling confirmed topographically specific stronger coupling between left PMd and right PMd (and right M1), when high-intensity TMS was applied to left PMd during left-hand grip. We conclude that left PMd can exert state-dependent interhemispheric influences on contralateral cortical motor areas relevant for a current motor task

Trial-by-trial fluctuations in the event-related electroencephalogram reflect dynamic changes in the degree of surprise

The P300 component of the human event-related brain potential has often been linked to the processing of rare, surprising events. However, the formal computational processes underlying the generation of the P300 are not well known. Here, we formulate a simple model of trial-by-trial learning of stimulus probabilities based on Information Theory. Specifically, we modeled the surprise associated with the occurrence of a visual stimulus to provide a formal quantification of the "subjective probability" associated with an event. Subjects performed a choice reaction time task, while we recorded their brain responses using electroencephalography (EEG). In each of 12 blocks, the probabilities of stimulus occurrence were changed, thereby creating sequences of trials with low, medium, and high predictability. Trial-by-trial variations in the P300 component were best explained by a model of stimulus-bound surprise. This model accounted for the data better than a categorical model that parametrically encoded the stimulus identity, or an alternative model of surprise based on the Kullback-Leibler divergence. The present data demonstrate that trial-by-trial changes in P300 can be explained by predictions made by an ideal observer keeping track of the probabilities of possible events. This provides evidence for theories proposing a direct link between the P300 component and the processing of surprising events. Furthermore, this study demonstrates how model-based analyses can be used to explain significant proportions of the trial-by-trial changes in human event-related EEG response

SPS quadrupole dog-leg and alignment post LS2

This document describes the functions of the horizontal and vertical dog-legs in the SPS and the effect of their removal for the injection and dump systems, following the LIU-SPS beam dump upgrad