CERN Research Articles

In Memoriam: Horst Wenninger (1938–2020)

Horst WenningerI had the pleasure and privilege to meet Horst Wenninger in the LAA Project context at the European Centre for Nuclear Research (CERN). The project was initiated by Antonino Zichichi...

Tailoring Leadership to the Phase-Specific Needs of Large Scale Research Infrastructures

'Large Scale Research Infrastructures' (LSRIs), a subcategory of megaprojects which incorporate a characteristic of a high or ‘super high’ level of technological uncertainty, are often undertaken as cooperative projects with long lead times by one or more national governments. A lack of research into the effect of the LSRI project’s lifecycle on the research organisation is apparent, particularly when scientists and engineers exercise freedom to organise the project directly. Two case studies used senior leadership selection as proxy for the LSRI project lifecycle using a contingency theory framework. These were the Tevatron (Fermi National Accelerator Laboratory, USA) and the Large Hadron Collider at the European Organisation for Nuclear Research (CERN). This LSRI lifecycle is mapped onto lifecycles used in theory and in policy. Previous research did not detect that these projects become institutionalised, so influencing the selection of new research organisation senior leadership according to its needs at that stage of its lifecycle. This represents something of a novelty as most contingency theory work is theoretical with few attempts to use it as a conceptual framework for empirical evidence. The findings indicate a second new understanding, that while the literature characterises a leadership style transition from democratic to authoritarian as the project progresses, LSRIs exhibit a reverse transformation, probably as a product of the characteristically high level of organisational technical competence. The construction of LSRIs maps better onto the traditional project lifecycle and the National Science Foundation’s large facility lifecycle than onto other lifecycles. There is a policy opportunity to commission a ‘generational survey’ upon the completion of an LSRI, to understand the characteristics of the ‘next big machine’.

Solitons and Instantons in Vacuum Stability: Physical Phenomena

In a previous paper [JCAP06, 033 (2018)] we have proved that it is possible to have a stable false vacuum in a potential that is unbounded from below. In this paper we discuss the Physics related to our theoretical and numerical results. We show that the results of recent CERN experiments lead to the fact that our vacuum is safe. We present a new mechanism, where the space-time dimension plays an important role, that explains why our Universe is stable. We provide new evidence that supports a process for the origin of matter-antimatter asymmetry recently introduced by other scientists. We examine confinement in the context of escape problems. We discuss multiverse, string theory landscape, and extra-dimensions using our framework. Finally, we use our solutions to introduce some hypotheses about Dark Matter and Dark Energy.

Cooperative and Multimodal Capabilities Enhancement in the CERNTAURO Human–Robot Interface for Hazardous and Underwater Scenarios

The use of remote robotic systems for inspection and maintenance in hazardous environments is a priority for all tasks potentially dangerous for humans. However, currently available robotic systems lack that level of usability which would allow inexperienced operators to accomplish complex tasks. Moreover, the task’s complexity increases drastically when a single operator is required to control multiple remote agents (for example, when picking up and transporting big objects). In this paper, a system allowing an operator to prepare and configure cooperative behaviours for multiple remote agents is presented. The system is part of a human–robot interface that was designed at CERN, the European Center for Nuclear Research, to perform remote interventions in its particle accelerator complex, as part of the CERNTAURO project. In this paper, the modalities of interaction with the remote robots are presented in detail. The multimodal user interface enables the user to activate assisted cooperative behaviours according to a mission plan. The multi-robot interface has been validated at CERN in its Large Hadron Collider (LHC) mockup using a team of two mobile robotic platforms, each one equipped with a robotic manipulator. Moreover, great similarities were identified between the CERNTAURO and the TWINBOT projects, which aim to create usable robotic systems for underwater manipulations. Therefore, the cooperative behaviours were validated within a multi-robot pipe transport scenario in a simulated underwater environment, experimenting more advanced vision techniques. The cooperative teleoperation can be coupled with additional assisted tools such as vision-based tracking and grasping determination of metallic objects, and communication protocols design. The results show that the cooperative behaviours enable a single user to face a robotic intervention with more than one robot in a safer way.

Influence of ion-induced secondary electron emission parameters in PICMC plasma simulations with experimental validation in DC cylindrical diode and magnetron discharges

Niobium thin films are used at CERN (European Organization for Nuclear Research) for coatings of superconducting radio-frequency (SRF) accelerating cavities. Numerical simulations can help to better understand the physical processes involved in such coatings and provide predictions of thin film properties. In this article, particle-in-cell Monte Carlo 3D plasma simulations are validated against experimental data in a coaxial cylindrical system allowing both DC diode and DC magnetron operation. A proper choice of ion induced secondary electron emission parameters enables to match experimental and simulated discharge currents and voltages, with argon as the process gas and niobium as the target element. Langmuir probe measurements are presented to further support simulation results. The choice of argon gas with a niobium target is driven by CERN applications, but the methodology described in this paper is applicable to other discharge gases and target elements.Validation of plasma simulations is the first step towards developing an accurate methodology for predicting thin film coatings characteristics in complex objects such as SRF cavities.

Discoveries of the pentaquark states

Protons and neutrons are not fundamental particles, instead are formed by quarks. Thousands of multi-quark particles were discovered in cosmic rays or particle accelerators. However, within the past decades after the quark model was proposed by Gell-Mann and Zweig, only two categories of strongly interacting particles were known: Baryons (such as protons and neutrons) that are made from three quarks, and mesons that are made from one quark and one antiquark. But what other configurations of quarks and antiquarks can form a particle? This question is theoretically difficult to answer. Yet new particles with different combinations of quarks keep popping up in experiments. In 2015, the best evidence for the existence of an exotic type of particle called as pentaquark, a never-before-seen formation of five quarks, was discovered by physicists working on the Large Hadron Collider beauty (LHCb) experiment at European Organization for Nuclear Research (CERN). The detection of this particle is a major breakthrough in learning more about the nature of the strong forces that bound quarks together. In a sample of about 26000 Λ b 0 → J/ψK − p decays collected by the LHCb detector, a significant enhancement structure was observed in the J/ψp mass distribution. The pentaquark signal populated well separatedly from those contributions of Λ * → K − p on the “Dalitz” plot using the K–p and J/ψp invariant mass-squared as independent variables. The amplitude analysis revealed two pentaquark states were needed to describe dataset. They were formally named as Pc(4450)+ and Pc(4380)+ with statistical significances greater than 9 standard deviations: One has a mass of (4449.8 ±1.7±2.5) MeV and a width of (39 ±5±19) MeV, while the other is wider, with a mass of (4380 ±8±29) MeV and a width of (205 ±18±86) MeV. Both pentaquarks that LHCb physicists observed decaying strongly into a J/ψ particle and a proton, must have a minimal quark content of c c ¯ uud, and thus are charmonium pentaquarks. Recently the analysis has been reoptimized based on the data collected to date. A sample of 2.5×105 Λ b 0 → J/ψK − p decays was selected, nine times more than those used in the previous analysis. A new pentaquark state Pc(4312) was discovered with a mass near 4312 MeV. The Pc(4450) state was found to be the superposition of two nearby states at 4440 and 4457 MeV respectively. In an attempt to interpret the discoveries by the LHCb experiment, the pentaquark was conjectured as a tightly bound system of all five quarks, or a weakly bound “molecular” system of a baryon and a meson. Accurate description of a multi-quark system using the theory of the strong force and quantum chromodynamics (QCD) is an extremely difficult problem. In fact, there are many combinations how five quarks are bound within the pentaquark. The five quarks could be tightly bound within a single structure, for example. Another possibility is that a quark and an antiquark are bound together to form a meson and the remaining three quarks form a baryon. The meson and baryon could then be bound to each other to create a structure resembling a subatomic molecule. Exploring the structure of pentaquarks as one of novel frontiers in high energy physics paves a new era to study the nature of strong interactions, which is an important stepping-stone in our good understanding of the strong force, the least well known of the four forces in nature.

Simplified stiffness analysis for degraded single lap joints in the space sector – Comparative analytical and finite element analysis

Considering the aerospace sector, the use of adhesively bonded joints is constantly increasing over the last decades. Due to its lightweight and capability of joining various materials with different coefficient of thermal expansion, this joining technique offers many benefits over conventional methods like rivets, screws and welding. On the other hand, structural adhesives consists of polymer chains that can be severely affected by the environment. An example of such an environmental effect is the interaction of the polymer chains of the adhesive with ionizing radiation in space. Nevertheless in the literature, the influence of ionizing radiation on the mechanical properties of epoxides is covered but not well understood. The present work describes a method of determining the stiffness of an adhesively bonded single lap joint (SLJ) using closed form solution equations. This analytical approach is compared with a numerical model. The mechanical properties of the adhesive in both models is degraded due to irradiation, based on experiments conducted by the European Organization for Nuclear Research (CERN). The results show that the degradation of the mechanical properties of the adhesive layer has a significant influence on the joint stiffness. This effect increases with growing adhesive layer thickness. Comparing the results with a finite element model, it is shown that the developed calculation scheme overestimates the stiffness of the SLJ. This is caused by the neglection of bending stresses within the adherends.

Deformability Tests of Pure Niobium

A research team at the University of Miskolc’s Faculty of Materials Science and Technology has signed a cooperation agreement with the Geneva-based European Organization for Nuclear Research (CERN) for testing of the materials employed in the Crab Cavities will be installed in the next generation of the LHC (the so-called High Luminosity Large Hadron Collider – HL-LHC). At the University of Miskolc, high purity niobium rolling experiments were carried out in conventional (unidirectional) and cross-rolled manners in order to increase the deep drawability of the final sheet. The deformability of niobium was measured by Watts-Ford and compression tests. The microstructure and anisotropy (texture) results of the initial material and the straight-rolled products are reported.

Precision Timing in the CMS MTD Barrel Timing Layer With Crystal Bars and SiPMs

The Compact Muon Solenoid (CMS) detector at the European Council for Nuclear Research (CERN) Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the high-luminosity LHC (HL-LHC). In particular, a new timing layer will measure minimum ionizing particles (MIPs) with a time resolution of ~30–40 ps and hermetic coverage up to a pseudorapidity of $\left |{ \eta }\right |=3$ . The precision time information from this detector will reduce the effects of the high levels of pileup expected at the HL-LHC and will bring new and unique capabilities to the CMS detector. This MIP Timing Detector (MTD) will consist of a central barrel timing layer (BTL) based on L(Y)SO:Ce crystals read out with silicon photomultipliers (SiPMs) and two end-caps instrumented with radiation-tolerant low-gain avalanche detectors (LGADs). With the goal of maximizing the detector performance within the stringent constraints of space, cost, and channel count, the BTL exploits elongated crystal bars, each read out with two SiPMs. This unusual geometry enables the instrumentation of large surfaces while minimizing the active area of the photodetectors and thus noise and power consumption. This article presents a summary of the research and development studies carried out to optimize this crystal-based technology and key beam test results in which the target time resolution of 30 ps has been achieved.

Graphene Sensor Goes Nuclear

A UK-based company’s development of a graphene sensor has led directly to a working partnership with CERN, the European Organization for Nuclear Research.

Thermal Neutron-Induced SEUs in the LHC Accelerator Environment

In addition to high-energy hadrons, which include neutrons, protons, and pions above 20 MeV, thermal neutrons (ThNs) are a major concern in terms of soft error rate (SER) for electronics operating in the large hadron collider (LHC) accelerator at the European Organization for Nuclear Research (CERN). Most of the electronic devices still contain Boron-10 inside their structure, which makes them sensitive to ThNs. The LHC radiation environment in different tunnel and shielded areas is analyzed through measurements and FLUKA simulations, showing that the ThN fluence can be considerably higher than the high-energy one, up to a factor of 50. State-of-the-art commercial-off-the-shelf (COTS) components such as SRAM, field-programmable gate arrays (FPGA), and Flash memories of different technologies are studied to derive the expected single-event upset (SEU) rate due to ThNs, relative to the high-energy hadron contribution. We find that for the studied parts and most of the accelerator applications, ThNs are the dominating source of upsets with respect to the high energy particles yielding even to neglect the latter in some cases. Indeed, they can induce, in electronics, up to more than 90% of the total upsets. The estimation is performed also for ground-level and avionic applications, and although in general, ThNs are not the main source of SER, in Flash memories they can play the same role as high energy neutrons. Related radiation hardness assurance (RHA) considerations for the qualification of components and systems against ThNs are presented.

Enhanced growth rate of atmospheric particles from sulfuric acid

Abstract. In the present-day atmosphere, sulfuric acid is the most important vapour for aerosol particle formation and initial growth. However, the growth rates of nanoparticles (<10 nm) from sulfuric acid remain poorly measured. Therefore, the effect of stabilizing bases, the contribution of ions and the impact of attractive forces on molecular collisions are under debate. Here, we present precise growth rate measurements of uncharged sulfuric acid particles from 1.8 to 10 nm, performed under atmospheric conditions in the CERN (European Organization for Nuclear Research) CLOUD chamber. Our results show that the evaporation of sulfuric acid particles above 2 nm is negligible, and growth proceeds kinetically even at low ammonia concentrations. The experimental growth rates exceed the hard-sphere kinetic limit for the condensation of sulfuric acid. We demonstrate that this results from van der Waals forces between the vapour molecules and particles and disentangle it from charge–dipole interactions. The magnitude of the enhancement depends on the assumed particle hydration and collision kinetics but is increasingly important at smaller sizes, resulting in a steep rise in the observed growth rates with decreasing size. Including the experimental results in a global model, we find that the enhanced growth rate of sulfuric acid particles increases the predicted particle number concentrations in the upper free troposphere by more than 50 %.

Nano-Games for Cultural Venues: the HEAL game

Many are the times when visitors leave an exhibition without a clue about its message. In an effort to eliminate this phenomenon, museums, institutes and organisations (MIOs) adopt more attractive, engaging and fun content to provide a high quality and fast learning experience. Games seem to be an interesting suggestion to this approach but they are time consuming. To this end, we introduce nano-games. We define nano-games as short, easy to master, self–contained games of a single level of difficulty, having basic and direct rules that stay unaltered throughout the play and challenge players with clearly defined goals reachable within tens of seconds of gameplay. This approach has been adopted and evaluated in the premises of European Center for Nuclear Research (CERN).

Single Event Upsets characterization of 65 nm CMOS 6T and 8T SRAM cells for ground level environment

We present experimental results of the cross-section related to cosmic-ray irradiation at ground level for minimum-sized six-transistor (6T) and eight-transistor (8T) bit-cells SRAM memories implemented on a 65 nm CMOS standard technology. Results were obtained from accelerated irradiation tests performed in the mixed-field irradiation facility of the CERN High-energy Accelerator test facility (CHARM) at the European Organization for Nuclear Research in Geneva, Switzerland. A 1.45× higher SEU cross-section was observed for 6T-cell designs despite the larger area occupied by the 8T cells (1.5× for MCU). Moreover, the trend for events affecting multiple bits was higher in 6T-cells. The cross-section obtained values show that the memories have enough sensitivity to be used as a radiation monitors in high energy physics experiments.

A Feature Selection-based Approach for the Identification of Critical Components in Complex Technical Infrastructures: Application to the CERN Large Hadron Collider

Complex Technical Infrastructures (CTIs) are large-scale systems made of tens of thousands of interdependent components organized in complex hierarchical architectures. They evolve in time in a way that at one point their functional logic may be more complex than originally designed, and, therefore, traditional reliability/risk importance measures cannot be used for identifying the critical components on which the protection and recovery efforts should be primarily allocated. We propose an approach for identifying the most critical components based on the large amount of operational data collected from the CTI monitoring systems over long time periods and under different operational settings. The underlying idea is to develop binary classifiers to associate different combinations of measured signals to the CTI operating or failed state. The critical CTI components are those whose condition monitoring signals allow optimally classifying the CTI state. To identify the signals and to build the classifier, we consider a feature selection wrapper approach based on the combined use of Support Vector Machine classifiers and the Binary Differential Evolution algorithm for optimization. The approach is successfully applied to a real dataset collected from the CERN (European Centre for Nuclear Research) Large Hadron Collider, a CTI for experiments of physics.

Microelectronic test structures for the development of a strip sensor technology for high energy physics experiments

The planned upgrade of the Large Hadron Collider, the HL-LHC, requires the development of improved tracking silicon sensors for the main CERN experiments. These devices must fulfil the specifications established by the different detectors for the adverse HL-LHC working conditions, in order to guarantee the proper performance of the tracking systems during the lifetime of the experiments. In the framework of the ATLAS Inner-Tracker sensor Market Survey, a prototype strip sensor layout has been designed by the collaboration, and fabricated in 6-inch substrates by Infineon Technologies AG. This work presents a set of test structures included in this prototype, capable to evaluate key device and technological parameters as strip implant resistivity, bias resistance, coupling capacitance, surface currents, or the influence of the sensor edge design in device breakdown voltage. A complete analysis of these parameters before and after proton and gamma irradiations, up to fluences and doses similar to the ones expected in the future HL-LHC experiments, is presented. This study shows the relevance of microelectronic test structures in the development of technologies of tracking silicon sensors for High Energy Physics experiments.

A Bayesian framework to update scaling factors for radioactive waste characterization

Nuclear power plants and research facilities commonly employ the so-called scaling factor (SF) method to quantify the activity of difficult-to-measure (DTM) radionuclides within their radioactive waste packages. The method relies on the establishment of a relationship between an easy-to-measure (ETM) radionuclide, called key nuclide (KN), and difficult-to-measure radionuclides, after the collection of a representative sample from the waste population. The distribution of the scaling factors, as well as the parameters defining the distribution, can change over time. Therefore, the accuracy of the calculated activity of the DTM radionuclides depends on the capacity of the scaling factor method to follow the time evolution of the waste population. In practice, waste producers collect periodically new samples from the waste population and check the variation and the validity of the scaling factors. In this article, we present a simple Bayesian framework to update scaling factors when a new data set becomes available. The method is tested and validated for radioactive waste produced at CERN (European Organization for Nuclear Research) and can be easily implemented for waste of different origin.

Development and qualification of triple-GEM detector built with large size single mask foils produced in India

The Gas Electron Multiplier (GEM) is the new age detector for nuclear and particle physics experiments, which was first developed by the European Center for Nuclear Research (CERN). It is comprised of an excellent insulator (Kapton/Apical) having a thickness of 50 μm which is covered with 5 μm copper layer on both sides and pierced by a regular array of holes. From its invention, CERN has been the sole supplier of the GEM foils until recently when few private companies started manufacturing GEM foils under the transfer of technology (TOT) from CERN. However, it's a long process to validate the foils delivered by these companies to claim that the GEM detectors made from them are compatible with high scientific standards. Along these lines, an India based company Micropack Pvt. Ltd. began fabricating both double and single mask GEM foils; at first Micropack produced 10 × 10 cm2 double mask foils which were tested both at foil and detector level by University of Delhi (DU) and it was confirmed to satisfy the required standards. Because of the double mask technique, the size of the GEM foil was constantly constrained so to overcome the confinement in size of GEM foils the single mask technique was developed in 2010. Micropack produced the first batch of 30 × 30 cm2 single mask foils in a joint effort with DU. A triple-GEM detector was constructed using these foils to test the fundamental quality controls, which include effective gain measurement, energy spectrum, and gain uniformity. Along with this, we will also report on the few advance studies which include discharge probability, rate capability, and charging up for this detector and foils.

Radiation Environment in the LHC Arc Sections During Run 2 and Future HL-LHC Operations

The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) is the largest accelerator in the world, spanning a circumference of 26.7 km. During its operation, small fractions of the beams are being continuously lost. This leads to mixed-field radiation that might affect electronic equipment through both cumulative and single-event effects. This article considers the radiation environment during Run 2 (years 2015-2018) in the LHC arc sectors that constitute approximately 70% of the accelerator, housing a huge amount of electronics. There, the main magnets' configuration is periodic, and the main contributor to losses is the interaction of the beams with residual gas molecules, resulting in relatively low-radiation levels, as opposed to different parts of the LHC. However, as presented, there are locations where losses are no longer dominated by residual gas. In these locations, radiation levels are higher by up to more than two orders of magnitude and could, therefore, be problematic in terms of cumulative radiation effects on electronics. In this article, the dose measurements from beam loss monitors have been combined with the FLUKA simulation for the arc sectors in order to indirectly retrieve the residual gas densities and radiation profile under the magnet cryostats, at the equipment level, for the losses caused by residual gas. Estimations for the radiation levels in the arc sectors during the high-luminosity LHC era and potential implications for the electronics are discussed as well.

Analysis of uncoated LPGs written in B-Ge doped fiber under proton irradiation for sensing applications at CERN

In this contribution, a complete dissertation concerning the behavior of a Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser and exposed to proton irradiation during a recent extensive campaign performed at the European Organization for Nuclear Research (CERN) with a fluence of 4.4·1015 p∙cm−2 is provided. The experimental results have been thus combined for the first time to the best of our knowledge with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the ultra-high dose proton exposure. From the correlation between experimental and numerical analysis, the irradiation exposure was found to induce a maximal variation of the core effective refractive index of ~1.61·10−4, responsible of a resonance wavelength red shift of ~44 nm in correspondence of the highest absorbed radiation dose of 1.16 MGy. At the same time, a relevant decrease close to ~0.93·10−4 in the refractive index modulation pertaining to the grating was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The effect of the proton beam on the spectral response of the LPG device and on the optical fiber parameters was assessed during the relaxation phases, showing a partial recovery only of the wavelength shift without any relevant change in the dip visibility revealing thus a partial recovery only in the refractive index of the core while the reduction of the refractive index modulation observed during the irradiation remained unchanged.