European Spallation Source Facility Research Articles

Firmware and Software Implementation Status of the ICBLM and nBLM Systems for the ESS Facility

The European Spallation Source (ESS) is a neutron source powered by a 5 MW, 2 GeV superconducting proton linac which is currently being constructed in Lund. Due to high beam current, just a few microseconds of operation with a misaligned beam can melt the accelerating cavity wall. Therefore, a Beam Loss Monitor (BLM) system is necessary to protect hardware and personnel from the consequences of beam loss. The BLM’s main function is to inhibit beam production when excessively high beam losses are detected. Besides protection functionality, the system is anticipated to provide the means to monitor the beam losses during all modes of operation with the objective of preventing excessive machine activation. This paper concentrates on implementation for ionization chamber Beam Loss Monitor (ICBLM) and Neutron Sensitive Beam Loss Monitor (nBLM) systems. The required microsecond reaction time has been achieved due to the application of an FPGA. A single detector module was installed and successfully tested at LINAC4 at CERN, in the section where conditions are similar to the ones expected in the ESS linac. The summary of these tests is also included.

Mechanical engineering, design and structural health monitoring at the ESS facility to enable science

The European Spallation Source (ESS), which is established as a European Research Infrastructure Consortium (ERIC), is a multi-disciplinary research facility that is currently under construction. ESS has as vision to develop to a world class facility, enabling scientific breakthroughs in research related to materials, energy, health and the environment. The ESS facility is built by a collaboration of some 100 research institutes and universities. With its 5 MW average beam power, its linac will be the most powerful linac of all neutron spallation sources. Neutrons are obtained by delivering 2 GeV protons at a repetition rate of 14 Hz to the He-cooled solid tungsten rotating target. The Accelerator is built with a high percentage of In-Kind Contributions (IKC) with major accelerator systems being designed, prototyped and built outside ESS. The first major accelerator elements are now being assembled and tested with their first parts being installed. Future similar large-scale projects could likely be IKC-based, which is a powerful model. Within ESS, the Mechanical Engineering & Technology (MET) section is responsible for developing and maintaining mechanical engineering and design throughout the facility. The mechanical design is consolidated in the master model and available under the ESS Plant Layout, including all In-Kind Contributions as well as other related mechanical engineering content. Consequently, the MET section is also responsible for the design, development and supervision of the proton accelerator and tungsten target in terms of civil and infrastructure design for the physical plant. In parallel, ESS has set stringent goals for high availability and reliability on the machines during operations. In order to deliver these goals and monitor the aging status of critical parts of the machines, prototypes and one-of-a-kinds, the MET section has developed and currently implements Structural Health Monitoring (SHM) program on the accelerator primarily and other machines for Operations. The innovative strategy and application of Non-Destructive Testing for Machines (NDTM) is under development by the MET section with the leading benefit of utilizing the technology of Resonant Ultrasound Spectroscopy (RUS). Both reference and irradiated samples undergo RUS measurements to obtain spectral responses of the dedicated materials, for machine reliability and operations availability purposes.

Fatigue behavior of rolled and forged tungsten at 25°, 280° and 480 °C

Pure tungsten has been chosen as the target material at the European Spallation Source facility in Lund. Calculations show that the target temperature can reach 500 °C momentarily during the spallation process, leading to thermal fatigue. Target life estimations require fatigue data at different temperatures and this work focuses on generating such data for pure, unirradiated, rolled and forged tungsten in the range 25°–480 °C.For specimens oriented in the rolling direction, tensile tests at room temperature indicated Young's modulus values in the range 320–390 GPa, low levels of plasticity (<0.23%) and UTS values in the range 397 MPa (unpolished) and 705 MPa (Polished). UTS for forged specimens were around 500 MPa.Stress-controlled fatigue tests were conducted in the tensile regime, with a runout limit of 2 × 106 cycles. At 25 °C, unpolished specimens had fatigue limits of 150 MPa (rolling and transverse direction), and 175 MPa (forged). For polished specimens in the rolling direction, fatigue limits were higher at 237.5 MPa (25 °C) and 252.5 MPa (280 °C). The forged specimens showed slightly better fatigue properties and marginal cyclic hardening at 480 °C.

Management of Tritium in European Spallation Source

The European Spallation Source (ESS) will produce tritium via spallation and activation processes during operational activities. Within the location of ESS facility in Lund, Sweden site it is mandatory to demonstrate that the management strategy of the produced tritium ensures the compliance with the country regulation criteria. The aim of this paper is to give an overview of the different aspects of the tritium management in ESS facility. Besides the design parameter study of the helium coolant purification system of the target the consequences of the tritium releasing into the environment were also analyzed.Calculations shown that the annual release of tritium during the normal operations represents a small fraction from the estimated total dose. However, more refined calculations of migration of activated-groundwater should be performed for higher hydraulic conductivities, with the availability of the results on soil examinations. With the assumption of 100% release of tritium to the atmosphere during the occurring of the extreme accidents, it was found as well that the total dose complies with the constraint.

The ESS Based Neutrino Super Beam for CP Violation Discovery

After measuring the last neutrino mixing angle θ13 and finding it relatively large, the observation of CP violation in the leptonic sector is now reachable with the condition to have significantly more intense neutrino beams than the existing ones. For this θ13 value, it came out that going to the second oscillation maximum instead of the first one, provides more sensitivity to CP violation. The European Spallation Source facility in Lund, designed to accelerate protons to 2.0GeV at a repetition rate of 14Hz for neutron production, could also be used to produce a copious number of neutrinos. Doubling the frequency of its proton linac opens the possibility to operate the facility simultaneously for neutron and neutrino production. An accumulator ring would be needed to shorten the pulses from 2.86ms for neutrons to few μs in order to reduce to acceptable levels the electric current sent to the magnetic horn focusing charged mesons to acceptable levels for the neutrino production. This accumulator could also be used by the neutron facility to increase its performance. Coupled with a megaton Water Cherenkov far detector placed at the optimal distance, this facility could efficiently exploite the second oscillation maximum to cover a large fraction of the CP violation parameter δCP at 5 σ confidence level.

Spallation materials R&D: Remarks on progress and future

Pure tungsten has been chosen as the target material at the European Spallation Source facility in Lund. Calculations show that the target temperature can reach 500 °C momentarily during the spallation process, leading to thermal fatigue. Target life estimations require fatigue data at different temperatures and this work focuses on generating such data for pure, unirradiated, rolled and forged tungsten in the range 25°–480 °C.For specimens oriented in the rolling direction, tensile tests at room temperature indicated Young's modulus values in the range 320–390 GPa, low levels of plasticity (<0.23%) and UTS values in the range 397 MPa (unpolished) and 705 MPa (Polished). UTS for forged specimens were around 500 MPa.Stress-controlled fatigue tests were conducted in the tensile regime, with a runout limit of 2 × 106 cycles. At 25 °C, unpolished specimens had fatigue limits of 150 MPa (rolling and transverse direction), and 175 MPa (forged). For polished specimens in the rolling direction, fatigue limits were higher at 237.5 MPa (25 °C) and 252.5 MPa (280 °C). The forged specimens showed slightly better fatigue properties and marginal cyclic hardening at 480 °C.