Large Accelerators Research Articles

Radiochemical Research with Transactinide Elements in Switzerland.

Here, we present a review on a fundamental radiochemical research topic performed by Swiss scientists in national and international collaborations, utilizing large accelerator facilities at the Paul Scherrer Institute as well as abroad. The chemical investigation of the heaviest elements of the periodic table is a truly multidisciplinary effort, which allows scientists to venture into a variety of fields ranging from nuclear and radiochemistry to experimental and theoretical work in inorganic and physical chemistry all the way to nuclear and atomic physics. The structure and fundamental ordering scheme of all elements in the periodic table, as established more than 150 years ago, is at stake: The ever increasing addition of new elements at the heavy end of the periodic table together with a growing influence of relativistic effects, raises the question of how much periodicity applies in this region of the table. Research on the heaviest chemical elements requires access to large heavy-ion accelerator facilities as well as to rare actinide isotopes as target materials. Thus, this scientific area is inevitably embedded in joint international efforts. Its fundamental character ensures academic relevance and thereby substantially contributes to the future of nuclear sciences in Switzerland.

Managing Expectations: Instruments Versus Targets

AbstractShould policy communications aim at anchoring expectations of the policy instrument (“keep interest rates at zero until date τ”) or of the targeted outcome (“do whatever it takes to bring unemployment down to $y\%$”)? We study how the optimal approach depends on a departure from rational expectations. People have limited depth of knowledge and rationality, or form otherwise distorted beliefs about the behavior of others and the general equilibrium (GE) effects of policy. The bite of this distortion on implementability and welfare is minimized by target-based guidance if and only if GE feedback is strong enough. This offers a rationale for why central banks should shine the spotlight on unemployment when faced with a prolonged liquidity trap, a steep Keynesian cross, or a large financial accelerator.

Test Beams of the LPI Accelerating Complex Pakhra

In this paper, we report the characteristics of the generated beams, the extracted electron beam and the beam of secondary electrons/positrons, of the LPI accelerator complex Pakhra as of November 2019 for testing and calibrating detectors used in large accelerator and astrophysical experiments. At energies of 250–500 MeV of the electron beam ejected into Hall 1 from the S-25R synchrotron, its energy resolution is δ ~ 1% and the intensity can be changed by collimators in the range of 103–1010 s–1. The quasi-monochromatic beam of secondary electrons produced in Hall 2 typically has an energy in the range of 50–300 MeV, a corresponding energy resolution of δ = 14–2%, and an intensity of ~ 102 s–1. The performed simulation of the characteristics of the secondary positron beam allowed selecting the optimal geometry of the setup and showed good agreement with the experimental data obtained later.

Physics-based deep neural networks for beam dynamics in charged particle accelerators

This paper presents a novel approach for constructing neural networks which model charged particle beam dynamics. In our approach, the Taylor maps arising in the representation of dynamics are mapped onto the weights of a polynomial neural network. The resulting network approximates the dynamical system with perfect accuracy prior to training and provides a possibility to tune the network weights on additional experimental data. We propose a symplectic regularization approach for such polynomial neural networks that always restricts the trained model to Hamiltonian systems and significantly improves the training procedure. The proposed networks can be used for beam dynamics simulations or for fine-tuning of beam optics models with experimental data. The structure of the network allows for the modeling of large accelerators with a large number of magnets. We demonstrate our approach on the examples of the existing PETRA III and the planned PETRA IV storage rings at DESY.

Beam impedance minimization for accelerator beamline insertion devices.

Use of complex state-of-the art detectors and monitors is essential to carry out high-energy and nuclear physics experiments at accelerator/collider facilities. The detectors are used to monitor charged particle beam parameters at large accelerator facilities such as coherent light sources and to develop new state-of-the art accelerators. Improvements in beam quality and lifetime necessitate the advancement of the instrumentation for successful operation of the accelerator facilities. Minimization of the beam-line-inserted devices' influence on the beam is therefore one of the essential considerations during the design of such facilities and the preparation of experiments. In this paper, we suggest and discuss a roadmap to minimize this influence. It is developed using fundamental concepts and numerical modeling, and we show that this is a multi-stage and multi-parametric problem that needs careful consideration. To illustrate the roadmap, the vacuum vessel for the vertex locator detector (CERN) is used. The results are discussed and, using them, the steps and stages of the design optimization are suggested. The suggested procedure can be applied to optimize the design of any beamline insertion device and will contribute to the development of next generation particle/accelerator detectors and monitors.

Investigating the influence of the wire-arrays’ electrical parameters on the load current of the z-pinch drivers

Wire arrays are the typical loads which have been widely used in z-pinch research studies. When a large pulsed power accelerator is designed, the electrical parameters of the z-pinch loads including the inductance and the resistance (or the equivalent resistance) must be considered. In this paper, the inductance and the resistance of the single planar wire arrays were introduced from the experiments carried out on a Qiangguang accelerator (1.5 MA, 100 ns). The lumped-element circuit model of the wire array was established using the PSPICE software, and the model was verified by comparing the simulation results with the experimental results. The influence of the electrical parameters on the accelerator’s driving current is investigated. It shows that the inductance affects the rising edge and the peak value of the current, while the resistance mainly affects the current waveform after the stagnation of the wire array pinch load. The inductance model based on the zero-dimensional equation is compared with the inductance model based on the experimental data, and the result shows that the two different inductance models give almost the same pinch current. It can be concluded that the zero-dimensional model is valid in circuit simulation to investigate the peak current of the designed z-pinch accelerator.

Radio-frequency design and commissioning of a flexible waveguide for high-vacuum S-band applications

Flexible waveguides, which allow for greater deformation as compared to traditional hard waveguides, are highly useful for simplifying waveguide system assemblies. However, the peak powers of these waveguides have been limited to several megawatts in non-vacuum environments. Herein, a novel flexible waveguide was developed for the S-band (2856 MHz) with the aim of facilitating the interconnection of two hard waveguides. The flexible waveguide was composed of brass, and its surface was plated with oxygen-free high-conductivity copper for brazing with stainless steel flanges in a vacuum furnace. By connecting the stainless steel flanges together, it can be applied to a high-vacuum environment. The prototype exhibited good measurement results in low-power microwave tests; the results of a 72-h vacuum leak test showed satisfactory vacuum performance as well, and no obvious surface collapse was observed. High-power microwave commissioning was conducted between June and July 2019; the waveguide showed a maximum average power of approximately 2.7 kW. Unfortunately, the prototype was damaged after reaching that power level, which indicates the need for further optimization of the fabrication process. From our experiment, it is clear that the flexible waveguide cannot be used in large accelerators because of its average power limit.

The future of HEP software

Any attempt to predict any future subject includes in general two components: extrapolations of the current trends and discussions about possible surprises. The extrapolation of the trends based on the latest function derivatives seems to be the easiest one. However, one has to be careful with fashionable trends and associated hype peaks. When one looks at the HEP software in the past 40 years, one sees regions of stability, often coinciding with the development and exploitation of a large accelerator, but also big changes when the hardware or/and software technology permits large steps. These large steps are often associated with surprises unthinkable a few years before. These two observations will likely continue to be true for the coming few decades, if not more. This paper is an attempt to analyze the current function derivatives based on similar analysis many years ago, and also propose some directions and developments that may become key components for our future software.

High-energy high-luminosity e+e− collider using energy-recovery linacs

In this letter we present a novel approach for a high-energy high-luminosity electron-positron collider. Present designs for high-energy electron-positron colliders are either based on two storage rings with 100 km circumference with a maximum CM energy of 365 GeV or two large linear accelerators with a high energy reach but lower luminosity, especially at the lower initial CM energies. A shortcoming of the collider based on storage rings is the high electric power consumption required to compensate for the beam energy losses from the 100 MW of synchrotron radiation power [1]. We propose to use an Energy Recovery Linac (ERL) located in the same-size 100 km tunnel to mitigate this drawback. We show in this letter that using an ERL would allow large reduction of the beam energy losses while providing higher luminosity in this high-energy collider operating at or above 140 GeV center-of-mass energy. Furthermore, our approach allows for extending the CM energy to 500 GeV, which would enable double-Higgs production, and even to 600 GeV for tt‾H production.

Application of sub-cooled superfluid helium for cavity cooling at linac-based free electron lasers, energy recovery and proton linacs

In order to build a compact linear accelerator, high acceleration gradients of superconducting radio frequency (SRF) cavities have to be achieved. In many large accelerators, e.g. XFEL, CEBAF or SNS, operational limitations are caused either by a limit on available overall cooling power of refrigerators or on cooling capabilities of sc cavities. So, for the further improving of sc cavity cooling, it is possible to increase either a quality factor (Q 0) or to improve a heat transfer at the cavity surfaces. Application of a sub-cooled superfluid helium gives several advantages, e.g. higher heat flux densities, longer time for onset of a film boiling regime and shorter recovery time, reduced Kapitza resistances, etc. In the present paper, application of sub-cooled superfluid (sf) helium for linac-based Free Electron Lasers, Energy Recovery and Proton Linacs is considered. In order to limit the present discussion, its application to CEBAF/SNS-style cryomodules is discussed in detail. For operation at higher RF power levels, further cooling improvements of a fundamental power coupler are needed and design modifications also presented.

Stable operation of cryogenic system at 2K during the RF or magnet power variations

In the last 40 years several large laboratories, e.g. CERN, DESY, TJNAF, constructed the accelerators with large number of superconducting (sc) cavities or sc magnets operating at 2 or 4 K temperature levels. The sc cavity operation requires more stringent ranges of pressure variation than ones of sc magnets. In comparison to small testing benches or single cavities modules, for large accelerators a complicated controlling of refrigerator and cryogenic system is required. In the present paper, a review of controlling principles and loops, typically applied for the controlling of liquid helium (LHe) level and pressure for large accelerators is presented. Other possible control loops, e.g. cascade control or multivariable feed-back (or with feed-forward option), are discussed. Activities related to the commissioning of control loops and some supporting measurements are mentioned. Experimental data on investigation of gas/liquid thermal equilibrium are also presented.

Experimental measurements on MLI performance from 20-60 K to 4.2 K

Future accelerators like the Future Circular Collider (FCC) under study at CERN, will be considerably larger than the Large Hadron Collider (LHC) presently in operation, with consequent increasing demands for cryogenically efficient cryostat solutions. MLI insulating systems remain the technology of choice for large accelerators due to the compromise they offer between thermal performance and cost-effectiveness. Thermal design solutions for cryostats can employ different combinations of thermal shields operating at intermediate temperatures, with optimally chosen MLI solutions. Data in literature is scarce for MLI performance at 4.2 K when operating with a thermal shield at a temperature between 60 K and 20 K. Therefore, a dedicated test program for the qualification of MLI samples is underway at CERN, exploring different MLI configurations, shielding radiative heat from 20-60 K to 4.2 K and with residual gas pressures between 1×10−6 and 1×10−4 mbar. This paper presents results from the test campaign.

Fabrication of 1 m long multi layered superconducting coated conductor with high engineering critical current density

Cable conductors fabricated by bundling coated conductors to increase the transport current have been developed for large-scale electric applications such as highly magnetic field magnets, large accelerators and fusion reactors. Various types of cable conductors (CORC cables, Roebel cables, TSTC and round wires) have been fabricated using coated conductors; however, these cable conductors do not have a high engineering critical current density (Je) required high performance in large-scale applications. In this study, new high temperature superconducting (HTS) multilayered conductors have been fabricated to increase the critical current and Je of coated conductors as cable conductors. The property of easy exfoliation owing to the weak c-axis strength of coated conductors is used to fabricate multi layered HTS conductors. In order to stack and bond multiple-HTS layers on one substrate (MHOS), a silver diffusion bonding technique using only a silver plated coated conductor is adopted. The MHOS conductor consists of multiple, biaxial-, textured, superconducting layers without any intermediate epitaxial grown buffer layer or solder layer between them. A 1 m long 4-MHOS conductor was successfully fabricated to proposed fabrication process; it exhibited a high critical current (2484 A/12 mm-w) and high engineering critical current density (Je = 0.12 MA cm−2). The critical current of the fabricated MHOS conductor at liquid nitrogen temperature (65–77 K) with a magnetic field ranging from 0 to 6 T increased proportionally with the number of superconducting layers.

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.

Beyond HEP: Photon and accelerator science computing infrastructure at DESY

DESY is one of the largest accelerator laboratories in Europe. It develops and operates state of the art accelerators for fundamental science in the areas of high energy physics, photon science and accelerator development. While for decades high energy physics (HEP) has been the most prominent user of the DESY compute, storage and network infrastructure, various scientific areas as science with photons and accelerator development have caught up and are now dominating the demands on the DESY infrastructure resources, with significant consequences for the IT resource provisioning. In this contribution, we will present an overview of the computational, storage and network resources covering the various physics communities on site. Ranging from high-throughput computing (HTC) batch-like offline processing in the Grid and the interactive user analyses resources in the National Analysis Factory (NAF) for the HEP community, to the computing needs of accelerator development or of photon sciences such as PETRA III or the European XFEL. Since DESY is involved in these experiments and their data taking, their requirements include fast low-latency online processing for data taking and calibration as well as offline processing, thus high-performance computing (HPC) workloads, that are run on the dedicated Maxwell HPC cluster. As all communities face significant challenges due to changing environments and increasing data rates in the following years, we will discuss how this will reflect in necessary changes to the computing and storage infrastructures. We will present DESY compute cloud and container orchestration plans as a basis for infrastructure and platform services. We will show examples of Jupyter notebooks for small scale interactive analysis, as well as its integration into large scale resources such as batch systems or Spark clusters. To overcome the fragmentation of the various resources for all scientific communities at DESY, we explore how to integrate them into a seamless user experience in an Interdisciplinary Data Analysis Facility.

Time-of-flight mass spectrographs of high mass resolving power

The masses of charged atoms and molecules were first investigated by laterally dispersive sector field mass analyzers, which early on already achieved high mass resolving powers. Equally, high mass resolving powers were achieved by time-of-flight mass analyzers during the last decades. These measurements became possible when fast and precise electronic circuitries became available. Such techniques have been developed and used extensively for the mass analysis of short-lived nuclei, whose mass values reveal insight in processes that describe the formation of elements in star explosions. Precise mass determinations of short-lived ions have been performed for energetic ions in large accelerator storage rings as well as for low-energy ions in time-of-flight mass spectrographs with long flight paths. Similarly, precise mass measurements can also be performed for molecular ions that help to reveal the structure of molecules. In case of very high mass resolving powers, the mass determination of molecular ions can be so high that the measured ion mass directly reveals the molecule’s sum formula.

Numerical Investigation of Th-229 Production in an Accelerator Driven System Reactor

The expected increase in radionuclide demand for treatment of various tumor diseases has led to the investigation of alternative production routes to provide sufficient amount of medical isotopes [1]. In Targeted Alpha Therapy (TAT), there is a present and future need for the Ac-225 and Bi-213, as the most promising alpha emitting isotopes, one of the limited ways to provide these radioisotopes is by production of Th-229 in reactor route [2][3]. The present study conducted to investigate the production of Th-229 to expand the availability of Ac-225 and Bi-213 in innovative nuclear reactor concept like Accelerator Driven System reactor (ADS)[4], which is a subcritical reactor and currently in development that predict to play an important role in the transmutation process of heavy elements and isotopes production. The possibility of producing Th-229 from neutron transmutation of Ra-226 are numerically investigated for simple model of ADS reactor consist of two zones, inner region with fast neutron spectra and outer region with thermal neutron spectra, and the subcritical core coupled with external neutron source. The calculations of transmutation behavior and mass ratio for the produced isotopes are conducted by using Monte Carlo N-particle Transport (MCNPX) code. This research was supported by International Center for Theoretical Physics and The Institute of International Education Scholar Rescue Fund. My deep thanks to colleagues from Institute for Safety Problems of Nuclear Power Plants, Ukraine who provided expertise that assisted the research. [1]E. R. Birnbaum, L. J. Bitteker, A. Couture, and M. E. Fassbender, “Ac and Ra-223 Production via 800 MeV Proton Irradiation of Natural Thorium Targets,” vol. 836.[2]J. R. Griswold et al., “Large scale accelerator production of Ac-225: Effective cross sections for 78–192 MeV protons incident on Th-232 targets,” Appl. Radiat. Isot., 2016.[3]S. Hogle et al., “Reactor production of Thorium-229,” Appl. Radiat. Isot., vol. 114, pp. 19–27, 2016.[4]H. Aït Abderrahim, P. Baeten, D. De Bruyn, and R. Fernandez, “MYRRHA - A multi-purpose fast spectrum research reactor,” in Energy Conversion and Management, 2012, vol. 63, pp. 4–10.

Simulation and measurement of rarefied gas flow and neutral density profiles through a large multiaperture multigrid negative ion accelerator

In large multi-aperture, multi-grid negative-ion accelerator for fusion application, the background gas density in the electrostatic accelerator causes a loss of negative-ion current and the formation of dangerous stray particles. In addition, to sustain in dynamic equilibrium a sufficient gas pressure in the plasma ion-source, a very large pumping speed is typically necessary. This paper presents and compare simulations and measurements of gas flows and background pressure profiles, through the electrostatic accelerator of the SPIDER beam source, the full-size prototype source of the ITER neutral beam injectors. The gas pressure profiles through the ion accelerator were measured by multiple movable capacitive pressure gauges, mapping the uniformity of the profiles along nine beamlets at three different filling pressures. The gas flow simulations in molecular flow regime were performed with a large-scale view-factor model, and with a single-aperture periodic test particle Monte Carlo model. The models reproduced the measured pressure profiles but additionally, provided also the profiles of local gas density. The gas conductance and the profiles calculated with the full-scale gas flow model correctly reproduce the measured profiles, and the transversal non-uniformities over the 1.6 m × 0.6 m cross section. The calculated gas density profile is also verified by comparing the two different numerical approaches. The gas flow model validated at room temperature can be used to simulate the pressure profile during operation, in presence of gas heating and dissociation by the source plasma.

Formation and structure of Nb3Sn layers in bronze-processed superconductors under various intermediate heat treatments

Multifilamentary Nb3Sn-based superconducting wires are created and used for various superconducting magnetic systems such as thermonuclear reactors and future large accelerator projects. The crucial role in achieving high superconducting characteristics is played by the structure of Nb3Sn layers, which, in its turn, is determined by a number of factors, such as fabrication route, composition, annealing schedules, etc. In the present study the superconducting layers formation and structure have been studied by SEM and TEM after various regimes of intermediate heat treatments and two-staged diffusion annealing. Optimal heat treatment schedules for the formation of perfect nanocrystalline structure of Nb3Sn layers for an achievement of highest critical current densities have been revealed.

Observation of internal multiplication of nonequilibrium charge in irradiated silicon detectors at a temperature of 1.9K

The development of modern high-energy physics is a powerful incentive for the progress of its experimental base. The use of semiconductor devices is standard for large accelerators and experimental setups at LHC, CERN, and perspective as sensors for monitoring beam loss and radiation fields in superconducting magnets and accelerating resonators operating at superfluid helium temperature (1.9 K). In these problems, the optimal type of radiation sensor is a compact silicon detector, the use of which in harsh radiation environment in combination with helium temperatures is a non-trivial task. The most important characteristics of such devices are the distribution of the electric field in the volume and the parameters of charge carrier transport, which determines the detector signal. The study considers specific kinetics of charge collection in silicon detectors at a temperature of 1.9 K in situ irradiated by relativistic hadrons.