High Energy Physics Applications Research Articles

Measurements of the Strain Dependence of Critical Current of Commercial REBCO Tapes at 15 T Between 4.2 and 40 K for High Field Magnets

Author(s): Pierro, F; Delgado, M; Chiesa, L; Wang, X; Prestemon, SO | Abstract: Interest for high magnetic fields (g16 T) for applications in high energy physics (HEP) and fusion machines, requires the development of high current cables capable to withstand the large forces, mechanical and electromagnetic, experienced during manufacturing and operations. The critical current (Ic) of REBCO tapes depends on strain, magnetic fields, and operational temperatures. Understanding how these parameters affect the Ic of the conductor will be critical to develop robust high-current REBCO cables. However, there are limited reports on the strain dependence of Ic, in particular at high fields and elevated temperatures relevant for future high-field compact fusion reactor magnets. We present Ic of commercial REBCO tapes measured as a function of compressive and tensile strain (between-0.6% and +0.65%) at high magnetic fields (12 and 15 T) and different temperatures (within 4.2-40 K). Results at 4.2 and 20 K showed less than 5% reduction in the normalized Ic at high strain, while a stronger strain dependence was observed at 40 K. Samples tested at 12 T and 4.2 K showed similar strain dependence as 15 T and 4.2 K. In all tested conditions, the tape experienced reversible Ic reduction in both tension and compression. Finite element analysis was used to predict the residual thermal strain accumulated in the REBCO layer prior of testing to account for the effect of the cooldown. A method was also developed to account for the current sharing observed between the sample and the sample holder during the ramp of the current. Our results provide useful input for the development of high-field fusion and HEP magnets using REBCO conductors.

Radiation hardness of Ce-doped sol-gel silica fibers for High Energy Physics applications

Radiation hardness of Ce-doped sol-gel silica fibers for High Energy Physics applications

Characterisation of AMS H35 HV-CMOS monolithic active pixel sensor prototypes for HEP applications

Monolithic Active Pixel Sensors (MAPS) produced in High Voltage CMOS (HV-CMOS) technology are being considered for High Energy Physics applications due to the ease of production and the reduced costs. Such technology is especially appealing when large areas to be covered and material budget are concerned. This is the case of the outermost pixel layers of the future ATLAS tracking detector for the High Luminosity LHC. For experiments at hadron colliders, radiation hardness is a key requirement which is not fulfilled by standard CMOS sensor designs that collect charge by diffusion. This issue has been addressed by depleted active pixel sensors in which electronics are embedded into a large deep implantation ensuring uniform charge collection by drift. Very first small prototypes of hybrid depleted active pixel sensors have already shown a radiation hardness compatible with the ATLAS requirements. Nevertheless, to compete with the present hybrid solutions a further reduction in costs achievable by a fully monolithic design is desirable. The H35DEMO is a large electrode full reticle demonstrator chip produced in AMS 350 nm HV-CMOS technology by the collaboration of Karlsruher Institut für Technologie (KIT), Institut de F'isica d'Altes Energies (IFAE), University of Liverpool and University of Geneva. It includes two large monolithic pixel matrices which can be operated standalone. One of these two matrices was characterised at beam test before and after irradiation with protons and neutrons. Results demonstrated the feasibility of producing radiation hard large area fully monolithic pixel sensors in HV-CMOS technology. H35DEMO chips with a substrate resistivity of 200 Ωcm} irradiated with neutrons showed a radiation hardness up to a fluence of 1×1015 neq/cm2 with a hit efficiency of about 99% and a noise occupancy lower than 10-6 hits in a LHC bunch crossing of 25 ns at 150 V.

Dynamic Integration and Management of Opportunistic Resources for HEP

Demand for computing resources in high energy physics (HEP) shows a highly dynamic behavior, while the provided resources by the Worldwide LHC Computing Grid (WLCG) remains static. It has become evident that opportunistic resources such as High Performance Computing (HPC) centers and commercial clouds are well suited to cover peak loads. However, the utilization of these resources gives rise to new levels of complexity, e.g. resources need to be managed highly dynamically and HEP applications require a very specific software environment usually not provided at opportunistic resources. Furthermore, aspects to consider are limitations in network bandwidth causing I/O-intensive workflows to run inefficiently. The key component to dynamically run HEP applications on opportunistic resources is the utilization of modern container and virtualization technologies. Based on these technologies, the Karlsruhe Institute of Technology (KIT) has developed ROCED, a resource manager to dynamically integrate and manage a variety of opportunistic resources. In combination with ROCED, HTCondor batch system acts as a powerful single entry point to all available computing resources, leading to a seamless and transparent integration of opportunistic resources into HEP computing. KIT is currently improving the resource management and job scheduling by focusing on I/O requirements of individual workflows, available network bandwidth as well as scalability. For these reasons, we are currently developing a new resource manager, called TARDIS. In this paper, we give an overview of the utilized technologies, the dynamic management, and integration of resources as well as the status of the I/O-based resource and job scheduling.

Simulation study of Resistive Plate Chamber's (RPCs) capability for medical imaging applications

Resistive Plate Chambers (RPC) have attracted a lot of research attention since past two decades due to their special features and properties especially for high energy physics applications. In this paper its capability to be used for medical imaging applications is studied. The main focus of this paper is on the gamma detection efficiency and energy resolution of this detector for common medical imaging modalities. The gamma to electron converter material and its thickness for a multilayer converter configuration is optimized to improve the detection efficiency. Simulation results show that 200 μm thickness of Borosilicate glass resistive plate can suppress the scattered photons. Therefor it can distinguish the primary and scattered photons for PET imaging with good detection efficiency for the primaries. By using 50 layers of RPCs with 30–50 μm thickness of lead converters and 200 μm thickness of borosilicate glasses as resistive plates of RPCs, not only for 511 keV gamma, the detection efficiency of 15% can be achieved, but also the related signals of scatterd gammas at 425 keV and 325 keV energies in comparison to 511 keV are reduced 30% and 65%, respectively. The 2 μm and 10 μm thicknesses of Lead are also introduced as high detection efficiency converter material for CT and SPECT scans, respectively.

Improvement of response time in GAGG:Ce scintillation crystals by magnesium codoping

Dynamics of the population of the excited Ce states responsible for the luminescence response time in Gd3Al2Ga3O12:Ce scintillating crystals is studied by revealing the dynamics of nonequilibrium carriers in the picosecond domain. Optical pump and probe technique exploiting selective excitation of structural units of the crystal and probing the induced absorption as a function of time and spectral position is exploited. A fast response within a few picoseconds due to the absorption by holes at Gd ions and by electrons occupying the first excited state of Ce ions with the intracenter relaxation time of 500 fs are identified. Trapping of nonequilibrium electrons during their migration through the matrix to the emitting Ce ions are shown to be responsible for the slow component in the population of the excited Ce state. Elimination of the slow component is evidenced even at Mg codoping as low as 10 ppm. The elimination correlates with the acceleration of the response in coincidence time resolution experiments showing potential of GAGG:Ce, Mg in medical and high-energy physics applications.

Rings: An efficient Java/Scala library for polynomial rings

In this paper we briefly discuss Rings — an efficient lightweight library for commutative algebra. Polynomial arithmetic, GCDs, polynomial factorization and Gröbner bases are implemented with the use of modern asymptotically fast algorithms. Rings can be easily interacted or embedded in applications in high-energy physics and other research areas via a simple API with fully typed hierarchy of algebraic structures and algorithms for commutative algebra. The use of the Scala language brings a quite novel powerful, strongly typed functional programming model allowing to write short, expressive, and fast code for applications. At the same time Rings shows one of the best performances among existing software for algebraic calculations. Program summaryProgram Title:RingsProgram Files doi:http://dx.doi.org/10.17632/2k79hftjy9.1Licensing provisions: Apache 2.0Programming language: Java, ScalaNature of problem: Fast methods for rational function arithmetic, simplification of polynomial expressions, Gröbner bases and other related computer algebra methods naturally arising in physical applicationsSolution method: Efficient implementation of modern asymptotically fast algorithms in Java languageExternal routines: Java 8 and higher, Scala 2.11 or 2.12Additional comments: project page: https://github.com/PoslavskySV/rings,documentation: http://rings.readthedocs.io/en/latest/

Effect of gamma and beta radiation on I–V characterization of the solar cell panel

ABSTRACTOptoelectronic devices, widely used in high energy and nuclear physics applications, suffer severe radiation damage that leads to degradations in its efficiency. In this paper, the influence of gamma radiation (137Ce source) and beta radiation (90Sr source) on the photoelectric parameters of the Si solar cell, based on the I–V characterization at different irradiation exposer, has been studied. The penetrating radiation produces defects in the base material, may be activated during its lifetime, becoming traps for electron–hole pairs produced optically and, this will, decrease the efficiency of the solar cell. The main objective of the paper is to study and measure changes in the I–V characteristics of solar cells, such as efficiency, maximum current, maximum power, and efficiency, due to the exposure of solar systems to different doses of γ and β irradiations.

Computer simulation on homogeneity testing for weighted data sets used in HEP

Modified statistical homogeneity tests on weighted data samples are commonly used in high energy physics applications. We do typically apply the tests in order to test homogeneity of weighted and unweighted samples, e.g. Monte Carlo simulations compared to the real data measurements. The asymptotic approximation of p-value of our weighted variants of homogeneity tests are investigated by means of simulation experiments. The simulation is performed for various probability sample distributions. We show that the asymptotic characteristics of the weighted homogeneity tests are valid for the specific distribution of weights.

Machine learning challenges in theoretical HEP

In these proceedings we perform a brief review of machine learning (ML) applications in theoretical High Energy Physics (HEP-TH). We start the discussion by defining and then classifying machine learning tasks in theoretical HEP. We then discuss some of the most popular and recent published approaches with focus on a relevant case study topic: the determination of parton distribution functions (PDFs) and related tools. Finally, we provide an outlook about future applications and developments due to the synergy between ML and HEP-TH.

GQLink: an implementation of Quantized State Systems (QSS) methods in Geant4

Simulations in high energy physics (HEP) often require the numerical solution of ordinary differential equations (ODE) to determine the trajectories of charged particles in a magnetic field when particles move throughout detector volumes. Each crossing of a volume interrupts the underlying numerical method that solves the equations of motion, triggering iterative algorithms to estimate the intersection point within a given accuracy. The computational cost of this procedure can grow significantly depending on the application at hand. Quantized State System (QSS) is a recent family of discrete-event driven numerical methods exhibiting attractive features for this type of problems, such as native dense output (sequences of polynomial segments updated only by accuracy-driven events) and lightweight detection and handling of volume crossings. In this work we present GQLink, a proof-of-concept integration of QSS with the Geant4 simulation toolkit which stands as an interface for co-simulation that orchestrates robustly and transparently the interaction between the QSS simulation engine and aspects such as geometry definition and physics processes controlled by Geant4. We validate the accuracy and study the performance of the method in simple geometries (subject to intense volume crossing activity) and then in a realistic HEP application using a full CMS detector configuration.

Virtualization of the ATLAS software environment on a shared HPC system

The shared HPC cluster NEMO at the University of Freiburg has been made available to local ATLAS users through the provisioning of virtual machines incorporating the ATLAS software environment analogously to a WLCG center. This concept allows to run both data analysis and production on the HPC host system which is connected to the existing Tier2/Tier3 infrastructure. Schedulers of the two clusters were integrated in a dynamic, on-demand way. An automatically generated, fully functional virtual machine image provides access to the local user environment. The performance in the virtualized environment is evaluated for typical High-Energy Physics applications.

Theory of radiative electron polarization in strong laser fields

Radiative polarization of electrons and positrons through the Sokolov-Ternov effect is important for applications in high-energy physics. Radiative spin-polarization is a manifestation of quantum radiation reaction affecting the spin-dynamics of electrons. We recently proposed that an analogue of the Sokolov-Ternov effect could occur in the strong electromagnetic fields of ultra-high-intensity lasers, which would result in a build-up of spin-polarization in femtoseconds. In this paper we develop a density matrix formalism for describing beam polarization in strong electromagnetic fields. We start by using the density matrix formalism to study spin-flips in non-linear Compton scattering and its dependence on the initial polarization state of the electrons. Numerical calculations show a radial polarization of the scattered electron beam in a circularly polarized laser, and we find azimuthal asymmetries in the polarization patterns for ultra-short laser pulses. A degree of polarization approaching 9 % is achieved after emitting just a single photon. We develop the theory by deriving a local constant crossed field approximation (LCFA) for the polarization density matrix, which is a generalization of the well known LCFA scattering rates. We find spin-dependent expressions that may be included in electromagnetic charged-particle simulation codes, such as particle-in-cell plasma simulation codes, using Monte-Carlo modules. In particular, these expressions include the spin-flip rates for arbitrary initial polarization of the electrons. The validity of the LCFA is confirmed by explicit comparison with an exact QED calculation of electron polarization in an ultrashort laser pulse.

Observation of High Transformer Ratio Plasma Wakefield Acceleration.

Particle-beam-driven plasma wakefield acceleration (PWFA) enables various novel high-gradient techniques for powering future compact light-source and high-energy physics applications. Here, a driving particle bunch excites a wakefield response in a plasma medium, which may rapidly accelerate a trailing witness beam. In this Letter, we present the measurement of ratios of acceleration of the witness bunch to deceleration of the driver bunch, the so-called transformer ratio, significantly exceeding the fundamental theoretical and thus far experimental limit of 2 in a PWFA. An electron bunch with ramped current profile was utilized to accelerate a witness bunch with a transformer ratio of 4.6_{-0.7}^{+2.2} in a plasma with length ∼10 cm, also demonstrating stable transport of driver bunches with lengths on the order of the plasma wavelength.

Characterization of a CLYC detector for underground experiments

Large size detectors based on Cs2LiYCl6:Ce (CLYC) are capable of performing a combined γ-ray and neutron spectrometry and constitute a promising technology for a wide range of applications in nuclear and high energy physics. Due to their novelty, the comprehensive characterization of the performance of individual CLYC detectors is of great importance for determining their range of applicability. In this work we report on a wide series of measurements performed with a commercial 2”×2” CLYC crystal. Good energy and timing resolution values, of 4.7% (@ 662 keV) and 1340 ps (FWHM) respectively, were achieved, and a neutron/γ separation figure of merit value of 4.2 was obtained. A dedicated measurement for investigating the intrinsic background of the detector was performed at the Laboratorio Subterráneo de Canfranc (Spain). It evidenced a sizeable contamination in the detector materials which poses limits in the use of CLYC in low background experiments. In addition, detailed Monte Carlo simulations with the GEANT4 toolkit were performed for modelling the response function of the CLYC detector to γ-rays. An excellent agreement with the experimental data has been achieved.

Compact electromagnetic calorimeters based on oriented scintillator crystals

Experimental results show that the strong crystalline field of a single-element crystal, e.g. Si or W, may lead to a huge decrease in the electromagnetic shower length, if the beam direction is aligned with the crystal axes. The same effect has been recently investigated in a high-Z crystal scintillator, i.e., a lead tungstate (PbWO4). The effect of shower length reduction can be exploited to develop an innovative type of electromagnetic calorimeter based on oriented scintillator crystals with the key feature of a reduced volume w.r.t. the state of the art. Here we present a Geant4 simulation study of e.m. shower length decreasing when a e±∕γ beam is aligned with respect the PWO main crystal axes. The presented work opens the way for a variety of applications in high-energy physics and astrophysics. Such applications span from forward calorimeters/preshowers, to compact active beam dumps for light dark matter search, to pointing-strategy in satellite-borne gamma-ray telescope to decrease the required size to fully contain the e.m. shower generated by GeV to TeV particles for a point like source.

History, status and prospects of producing silicon sensors for HEP experiments at Infineon Technologies

Within this project we are developing single-sided AC-coupled silicon strip sensors and DC-coupled hexagonal pad sensors for applications in High Energy Physics (HEP) experiments. The project started with a feasibility study to re-produce the state-of-the art of silicon sensors of that time, which were based on high-resistivity n-type float-zone 6-inch silicon wafers. Later, the first silicon strip sensors on 8-inch p-type wafers were produced within this project. This influenced the decision of another project to build a silicon sensor based sampling calorimeter. This paper presents the history, current status, and prospects of this sensor development project, jointly conducted by the Institute for High Energy Physics (HEPHY) of the Austrian Academy of Sciences and Infineon Technologies AG.

Controlled injection using a channel pinch in a plasma-channel-guided laser wakefield accelerator

Plasma-channel-guided laser plasma accelerators make it possible to drive high-brilliance compact radiation sources and have high-energy physics applications. Achieving tunable internal injection of the electron beam (e beam) inside the plasma channel, which realizes a tunable radiation source, is a challenging method to extend such applications. In this paper, we propose the use of a channel pinch, which is designed as an initial reduction followed by an expansion of the channel radius along the plasma channel, to achieve internal controlled off-axis e beam injection in a channel-guided laser plasma accelerator. The off-axis injection is triggered by bubble deformation in the expansion region. The dynamics of the plasma wake is explored, and the trapping threshold is found to be reduced radially in the channel pinch. Simulation results show that the channel pinch not only triggers injection process localized at the pinch but also modulates the parameters of the e beam by adjusting its density profile, which can additionally accommodate a tunable radiation source via betatron oscillation.

Radiation hardness of Ce-doped sol-gel silica fibers for high energy physics applications.

The results of irradiation tests on Ce-doped sol-gel silica using x- and γ-rays up to 10kGy are reported in order to investigate the radiation hardness of this material for high-energy physics applications. Sol-gel silica fibers with Ce concentrations of 0.0125 and 0.05mol.% are characterized by means of optical absorption and attenuation length measurements before and after irradiation. The two different techniques give comparable results, evidencing the formation of a main broad radiation-induced absorption band, peaking at about 2.2eV, related to radiation-induced color centers. The results are compared with those obtained on bulk silica. This study reveals that an improvement of the radiation hardness of Ce-doped silica fibers can be achieved by reducing Ce content inside the fiber core, paving the way for further material development.

Performance profiling for brachytherapy applications

In many physics applications, a significant amount of software (e.g. R, ROOT and Geant4) is developed on novel computing architectures, and much effort is expended to ensure the software is efficient in terms of central processing unit (CPU) time and memory usage. Profiling tools are used during the evaluation process to evaluate the efficiency; however, few such tools are able to accommodate low-energy physics regions. To address this limitation, we developed a low-energy physics profiling system in Geant4 to profile the CPU time and memory of software applications in brachytherapy applications. This paper describes and evaluates specific models that are applied to brachytherapy applications in Geant4, such as QGSP_BIC_LIV, QGSP_BIC_EMZ, and QGSP_BIC_EMY. The physics range in this tool allows it to be used to generate low energy profiles in brachytherapy applications. This was a limitation in previous studies, which caused us to develop a new profiling tool that supports profiling in the MeV range, in contrast to the TeV range that is supported by existing high-energy profiling tools. In order to easily compare the profiling results between low-energy and high-energy modes, we employed the same software architecture as that in the SimpliCarlo tool developed at the Fermilab National Accelerator Laboratory (FNAL) for the Large Hadron Collider (LHC). The results show that the newly developed profiling system for low-energy physics (less than MeV) complements the current profiling system used for high-energy physics (greater than TeV) applications. Program summaryProgram title: Brachytherapy ProfilingProgram Files doi:http://dx.doi.org/10.17632/kv3rs8dxhp.1Licensing provisions: GNU GPLv3Programming language: C++, bash, R scriptExternal routines: Geant4 10.2 or laterPrerequisites: gcc 4.8 or higher, cmake 3.4 or higher, ROOT 5.22 or higher, FAST 6.2 or higher, Igprof 5.9.16 or higher, R 3.2.1 or higher, SQLite 3.3.6 or higherNature of problem: those that require a low-energy physics profiling system.Solution method: low-energy physics profiling system for brachytherapy applications.