European Spallation Source Research Articles

Gamma radiation calculations and gamma blocker design for the high-energy beam transport region of the European Spallation Source

Abstract The purpose of this paper is to present the Monte-Carlo calculations performed to design a special element called gamma blocker (GB), necessary to stop the gamma radiation in the Accelerator-to-Target (A2T) section of European Spallation Source (ESS) linac. Very high levels of gamma radiation emitted backward from the activated target through the beam pipe could effectively block any human intervention close to the beam transport system. The residual dose rate in the linac tunnel was calculated without and with different GBs as a function of time. The final GB material and dimensions are proposed.

Magnetic analysis and cross-talk fields for the ESS MEBT quadrupole magnet

The focusing lattice of the Medium Energy Beam Transport (MEBT) section of the European Spallation Source (ESS) linac is formed of 11 identical quadrupole magnets, the design of which was determined by beam requirements, spatial limitations and nearby instrumentation. Each magnet is only 89 mm long, produces quadrupole fields above 2.74T, and includes embedded steerer coil systems that excite dipole fields of up to 20G m. In this work, a comprehensive magnetic analysis of the ESS MEBT magnet will be presented through a combination of simulations and measurements. A magnetic model was updated and benchmarked with measurements. An integrated steerer system with coils wound on its return-arms was used to simplify mechanical design and improve magnetic field characteristics in comparison to others with coils integrated into their poletips. Steering field strength and harmonic content were studied versus quadrupole field excitation. Cross-talk fields were investigated for an MEBT doublet magnet system with magnetically shielded diagnostics positioned between its magnets. Due to this magnetic shielding, integrated quadrupole field was decreased by 3% and steering fields by 20% with respect to values calculated using a single magnet model.

High-Level Software Interface to the LLRF System Developed for the European Spallation Source Facility

The European Spallation Source (ESS) accelerator is composed of superconducting elliptical cavities. When the facility is running, the cavities are fed with an electric field from klystrons. Parameters of this field are monitored and controlled by the low-level radio frequency (LLRF) system. Its main goal is to keep the amplitude and phase at a given set point. The LLRF system is also responsible for the reference clock distribution. During operation, the cavities are periodically experiencing strain caused by the Lorentz force, while the high gradient of the electric field is generated for the beam acceleration. Even small changes in the physical dimensions of a cavity shift its resonance frequency. This phenomenon, called detuning, causes significant power losses. It is actively compensated by the LLRF control system, which can physically tune lengths of the accelerating cavities with stepper motors (slow, coarse-grained control) and piezo elements (active compensation during operation). This article describes the implementation and tests of the software supporting various aspects of the LLRF system and cavities management. The Piezo Driver management and monitoring tool is dedicated to a piezo controller device. The LO distribution application is responsible for configuration of the local oscillator. The cavity simulator tool was designed to provide access to properties of the hardware device, emulating behavior of the elliptical cavities. IPMI Manager Software was implemented to monitor the state of MicroTCA.4 crates, which are a major part of the LLRF system architecture. All applications have been created using the experimental physics and industrial control system (EPICS) framework and built in the ESS EPICS Environment (E3).

Dynamic Response of Spallation Volume to Beam Raster on the European Spallation Source Target

Dynamic Response of Spallation Volume to Beam Raster on the European Spallation Source Target

Evaluation of Feasibility of High-Power Long-Pulse Transformers Using Single-Layer and Pancake Winding Techniques

Solid-state klystron modulators are typically based on oil-immersed high-voltage (HV) pulse transformers because of their high performance, robustness, simplicity, and straightforward design. However, pulse transformer size is fundamentally linked to application pulse length, pulse power, and pulse rise time. For high-power applications transformer size quickly becomes very problematic when approaching pulse lengths on the order of one millisecond. This article presents a systematic study of the applicability of HV pulse transformers for such long-pulse high-power applications. Both the single-layer and pancake winding techniques are evaluated, keeping reduction of transformer volume as the main design objective. First, design models and efficient optimization procedures are developed. The proposed models are validated through circuit simulation, 3-D finite element analysis, and comparison with a commercial HV long-pulse transformer. Then, the developed optimization procedure is used in studying the evolution of pulse transformer size when pulse length is varied from 500 μs to 5 ms assuming peak pulse power requirements corresponding to that of the European Spallation Source (ESS) klystron modulators (115 kV, 100 A, 14 Hz). Finally, the developed trends are used to derive general analytical equations expressing maximum attainable pulse length as a function of application parameters and system constraints.

Accelerator development at the FREIA Laboratory

The FREIA Laboratory at Uppsala University focuses on superconducting technology and accelerator development. It actively supports the development of the European Spallation Source, CERN, and MAX IV, among others. FREIA has developed test facilities for superconducting accelerator technology such as a double-cavity horizontal test cryostat, a vertical cryostat with a novel magnetic field compensation scheme, and a test stand for short cryomodules. Accelerating cavities have been tested in the horizontal cryostat, crab-cavities cavities in the vertical cryostat, and cryomodules for ESS on the cryomodule test stand. High power radio-frequency amplifier prototypes based on vacuum tube technology were developed for driving spoke cavities. Solid-state amplifiers and power combiners are under development for future projects. We present the status of the FREIA Laboratory complemented with results of recent projects and future prospects.

Flexible Sample Environments for the Investigation of Soft Matter at the European Spallation Source: Part III—The Macroscopic Foam Cell

The European Spallation Source (ESS), which is under construction in Lund (Sweden), will be the leading and most brilliant neutron source and aims at starting user operation at the end of 2023. Among others, two small angle neutron scattering (SANS) machines will be operated. Due to the high brilliance of the source, it is important to minimize the downtime of the instruments. For this, a collaboration between three German universities and the ESS was initialized to develop and construct a unified sample environment (SE) system. The main focus was set on the use of a robust carrier system for the different SEs, which allows setting up experiments and first prealignment outside the SANS instruments. This article covers the development and construction of a SE for SANS experiments with foams, which allows measuring foams at different drainage states and the control of the rate of foam formation, temperature, and measurement position. The functionality under ESS conditions was tested and neutron test measurement were carried out.

Flexible Sample Environments for the Investigation of Soft Matter at the European Spallation Source: Part III—The Macroscopic Foam Cell

The European Spallation Source (ESS), which is under construction in Lund (Sweden), will be the leading and most brilliant neutron source and aims at starting user operation at the end of 2023. Among others, two small angle neutron scattering (SANS) machines will be operated. Due to the high brilliance of the source, it is important to minimize the downtime of the instruments. For this, a collaboration between three German universities and the ESS was initialized to develop and construct a unified sample environment (SE) system. The main focus was set on the use of a robust carrier system for the different SEs, which allows setting up experiments and first prealignment outside the SANS instruments. This article covers the development and construction of a SE for SANS experiments with foams, which allows measuring foams at different drainage states and the control of the rate of foam formation, temperature, and measurement position. The functionality under ESS conditions was tested and neutron test measurement were carried out.

ESS Cryogenic Controls Design

The European Spallation Source (ESS) is a neutron-scattering facility funded and supported in collaboration with 13 European countries in Lund, Sweden. Cryogenic cooling at ESS is vital particularly for the linear accelerator, the hydrogen target moderators, a test stand for cryomodules, the neutron instruments and their sample environments. The paper will focus on the control system design for the different cryogenic subsystems, hardware and software selected, industry and in-house development, advantages and disadvantages of the chosen setup and operational experience. There is also a lessons learned, feedback from providers and stakeholders and an outlook for further development described.

In-kind Contributions: Taxation of International Consortium Workers

In 2009, consistent with its objective to support and develop a European research infrastructure, the European Union (EU) created a new organizational form for research collaborations: the European Research Infrastructure Consortium (ERIC). Since then, 21 different ERICs have been established in the EU Member States; the largest being the European Spallation Source (ESS). The financing of this ERIC is dependent on in-kind contributions of goods and labour from the various Member States of the ERIC. This model of financing the ERIC instigates questions about which state has the right to tax that labour. In terms of taxation of the workforce, the ERIC is different compared to EU institutions or international research organizations such as the European Organization for Nuclear Research (CERN) for which taxes are levied at an organizational level rather than at a state level. This entails that the taxation of the workforce of the ERIC becomes more complex as the allocation of taxing rights on a state level is dependent of the applicable tax treaties entered into between the host states of the ERIC and Member States that are contributing towards the construction of the ERIC. Accordingly, the income from the work performed by the personnel may fall both within the scope of Article 15 as well as Article 19 of the OECD Model Tax Convention. European Research Infrastructure Consortium (ERIC), European Spallation Source (ESS), European Organization for Nuclear Research (CERN), OECD, Article 15, Article 19, public legal entities, government service, income from employment, in-kind contribution.

Resolving the LMA-dark NSI degeneracy with coherent neutrino-nucleus scattering

In the presence of non-standard neutrino interactions (NSI), a degeneracy exists in neutrino oscillation data, which involves the flipping of the octant of the mixing angle θ12 and the type of the neutrino mass ordering. In this article, we revisit the status of this degeneracy in the light of recent data on coherent elastic neutrino-nucleus scattering (CEνNS) from the COHERENT experiment. For general relative couplings to up and down quarks, the degeneracy is disfavoured at the 2σ level by the latest data but remains at a higher confidence level. We investigate the requirements of future CEνNS measurements to resolve the degeneracy with high significance. We find that a measurement involving both, electron and muon neutrino flavours and a target with a neutron-to-proton ratio close to 1 is required. For example, an experiment with a silicon target at the European Spallation Source can resolve the degeneracy at more than 4σ for arbitrary relative couplings to up and down quarks.

Flexible Sample Environment for the Investigation of Soft Matter at the European Spallation Source: Part II—The GISANS Setup

The FlexiProb project is a joint effort of three soft matter groups at the Universities of Bielefeld, Darmstadt, and Munich with scientific support from the European Spallation Source (ESS), the small-K advanced diffractometer (SKADI) beamline development group of the Jülich Centre for Neutron Science (JCNS), and the Heinz Maier-Leibnitz Zentrum (MLZ). Within this framework, a flexible and quickly interchangeable sample carrier system for small-angle neutron scattering (SANS) at the ESS was developed. In the present contribution, the development of a sample environment for the investigation of soft matter thin films with grazing-incidence small-angle neutron scattering (GISANS) is introduced. Therefore, components were assembled on an optical breadboard for the measurement of thin film samples under controlled ambient conditions, with adjustable temperature and humidity, as well as the optional in situ recording of the film thickness via spectral reflectance. Samples were placed in a 3D-printed spherical humidity metal chamber, which enabled the accurate control of experimental conditions via water-heated channels within its walls. A separately heated gas flow stream supplied an adjustable flow of dry or saturated solvent vapor. First test experiments proved the concept of the setup and respective component functionality.

Flexible Sample Environment for the Investigation of Soft Matter at the European Spallation Source: Part II—The GISANS Setup

The FlexiProb project is a joint effort of three soft matter groups at the Universities of Bielefeld, Darmstadt, and Munich with scientific support from the European Spallation Source (ESS), the small-K advanced diffractometer (SKADI) beamline development group of the Julich Centre for Neutron Science (JCNS), and the Heinz Maier-Leibnitz Zentrum (MLZ).Within this framework, a flexible and quickly interchangeable sample carrier system for small-angle neutron scattering (SANS) at the ESS was developed. In the present contribution, the development of a sample environment for the investigation of soft matter thin films with grazing-incidence small-angle neutron scattering (GISANS) is introduced. Therefore, components were assembled on an optical breadboard for the measurement of thin film samples under controlled ambient conditions, with adjustable temperature and humidity, as well as the optional in situ recording of the film thickness via spectral reflectance. Samples were placed in a 3D-printed spherical humidity metal chamber, which enabled the accurate control of experimental conditions via water-heated channels within its walls. A separately heated gas flow stream supplied an adjustable flow of dry or saturated solvent vapor. First test experiments proved the concept of the setup and respective component functionality.

Flexible Sample Environments for the Investigation of Soft Matter at the European Spallation Source: Part I—The In Situ SANS/DLS Setup

As part of the development of the new European Spallation Source (ESS) in Lund (Sweden), which will provide the most brilliant neutron beams worldwide, it is necessary to provide different sample environments with which the potential of the new source can be exploited as soon as possible from the start of operation. The overarching goal of the project is to reduce the downtimes of the instruments related to changing the sample environment by developing plug and play sample environments for different soft matter samples using the same general carrier platform and also providing full software integration and control by just using unified connectors. In the present article, as a part of this endeavor, the sample environment for in situ SANS and dynamic light scattering measurements is introduced.

Technical Specification of the Small-Angle Neutron Scattering Instrument SKADI at the European Spallation Source

Small-K Advanced DIffractometer (SKADI is a Small-Angle Neutron Scattering (SANS) instrument to be constructed at the European Spallation Source (ESS). SANS instruments allow investigations of the structure of materials in the size regime between Angstroms up to micrometers. As very versatile instruments, they usually cater to the scientific needs of communities, such as chemists, biologists, and physicists, ranging from material and food sciences to archeology. They can offer analysis of the micro- and mesoscopic structure of the samples, as well as an analysis of the spin states in the samples, for example, for magnetic samples. SKADI, as a broad range instrument, thus offers features, such as an extremely flexible space for the sample environment, to accommodate a wide range of experiments, high-flux, and optimized detector-collimation system to allow for an excellent resolution of the sample structure, short measurement times to be able to record the internal kinetics during a transition in the sample, as well as polarized neutron scattering. In this manuscript, we describe the final design for the construction of SKADI. All of the features and capabilities presented here are projected to be included into the final instrument when going into operation phase.

Simulation of the response of the Solid State Neutron Detector for the European Spallation Source

The characteristics of the Solid-state Neutron Detector, under development for neutron-scattering measurements at the European Spallation Source, have been simulated with a Geant4-based computer code. The code models the interactions of thermal neutrons and ionising radiation in the 6Li-doped scintillating glass of the detector, the production of scintillation light and the transport of optical, scintillation photons through the scintillator, en route to the photocathode of the attached multi-anode photomultiplier. Factors which affect the optical-photon transport, such as surface finish, pixelation of the glass sheet, provision of a front reflector and optical coupling media are compared. Predictions of the detector response are compared with measurements made with neutron and gamma-ray sources, a collimated alpha source and finely collimated beams of 2.5 MeV protons and deuterons.

Experimental study of concrete activation compared to MCNP simulations for safety of neutron sources

The neutron activation of shielding materials and the generated decay gamma radiation are well-known issues in terms of occupational exposure. Though the trace elements of shielding concretes can be dominant sources of the produced activity in such cases, their concentrations are often missing from the input data of shielding-related Monte Carlo simulations. For this reason, three concrete types were studied, that were considered in the European Spallation Source (ESS) ERIC. Their composition – including the trace elements – were determined via XRF, PGAA and NAA techniques. Realistic input data were developed for these materials, containing the parent elements of all the dominant radioisotopes, and were validated against measured data of neutron irradiation experiments.

A simulational study of the indirect-geometry neutron spectrometer BIFROST at the European Spallation Source, from neutron source position to detector position.

The European Spallation Source (ESS) is intended to become the most powerful spallation neutron source in the world and the flagship of neutron science in upcoming decades. The exceptionally high neutron flux will provide unique opportunities for scientific experiments but also set high requirements for the detectors. One of the most challenging aspects is the rate capability and in particular the peak instantaneous rate capability, i.e. the number of neutrons hitting the detector per channel or cm2 at the peak of the neutron pulse. The primary purpose of this paper is to estimate the incident rates that are anticipated for the BIFROST instrument planned for ESS, and also to demonstrate the use of powerful simulation tools for the correct interpretation of neutron transport in crystalline materials. A full simulation model of the instrument from source to detector position, implemented with the use of multiple simulation software packages, is presented. For a single detector tube, instantaneous incident rates with a maximum of 1.7 GHz for a Bragg peak from a single crystal and 0.3 MHz for a vanadium sample are found. This paper also includes the first application of a new pyrolytic graphite model and a comparison of different simulation tools to highlight their strengths and weaknesses.

A Pulse-Multiplication Proposal for MIRACLES, the Neutron TOF-Backscattering Instrument at the European Spallation Source

The fixed-energy window scan approach, for both elastic and inelastic modes, is a valuable tool to discriminate between motions activated when dynamical phase transitions occur in a sample as a function of time, temperature, pressure, electrical field or illumination. Considering that, on one hand, such variations can generate a weak signal, and on the other, high data throughput makes it possible to screen many samples during a beam time, pulse multiplication is an ideal strategy to optimize the intensity of the analyzed signal. To ensure this capability, a proposal for a future upgrade of MIRACLES, the neutron time-of-flight backscattering spectrometer at the European Spallation Source (ESS) under construction in Lund, is reported in this article. The concept for a new chopper layout relies on the extraction of several elastic pulses, ensuring an increase in the neutron total elastic intensity hitting the sample. This proposal can be extended to the inelastic counterpart. The premise is to maintain the original beamline layout without modification, either of the guide sections or of the current chopper layout of MIRACLES, thereby guaranteeing that minimal changes and impact will occur during the proposed upgrade. However, this also presents a significant challenge, namely, to achieve an efficient pulse multiplication within the width and the length of the guide and within the rising/decay time of the pulses. With the concept presented here, an increase in elastic intensity by a factor of 2.8 was obtained. This is analogous to performing elastic fixed window (EFW) measurements with an ESS source operating at 14 MW, widening considerably the performance capabilities of MIRACLES. The knowledge generated here is also valuable for the design of scientific instruments for the next generation of low-energy, accelerator-driven neutron sources.

Optimal Design of Electronic Bouncers for Long-Pulse High-Power Modulators

Modern high-voltage high-power pulsed modulators typically generate pulses by discharging energy stored in one or more capacitor banks into the load. The capacitor discharge manifests itself as output pulse droop which must be compensated for. To eliminate such droop, modulators utilizing pulse transformers require external circuitry and, typically, passive resonant bouncer circuits are used. For long-pulse applications, however, electronic bouncer circuits operated in closed loop are preferred due to their compactness, efficiency, precision, and resilience to aging effects. Electronic bouncers may also be used in applications with varying pulselength and/or pulse repetition rate. In this article, design models are developed for both the modulator capacitor bank as well as each electronic bouncer circuit component. The design models are integrated in a global optimization routine used to study design tradeoffs between the modulator capacitor bank and the electronic bouncer, as well as between system efficiency and system volume. An optimization case study based on European Spallation Source modulator requirements (pulse amplitude 115 kV/100 A, pulselength 3.5 ms, pulse repetition rate 14 Hz, combined pulse flat top ripple and droop <; 0.15%) is provided, and an optimal design solution is selected and validated through characterization in both circuit simulation and 3-D finite element analysis. Finally, the performance of the chosen electronic bouncer solution is compared to that of an optimized design based on the conventional passive resonant bouncer circuit.