The n_TOF facility at the European Laboratory for Particle Physics (CERN) is a top-class, high-brightness neutron spallation source dedicated to high-resolution neutron time-of-flight experiments. ...During CERN’s Long Shutdown 2 (LS2, 2019-2021), the facility’s neutron spallation target was upgraded and is now operating with its third-generation target. The target is based on a pure-Pb core cooled by gaseous nitrogen and has been designed to withstand the impact of a 20-GeV/
c
proton beam in bunches of 10
13
protons with a bunch duration of 6-8 ns RMS. The produced neutrons span 11 orders of magnitude in kinetic energy (from thermal to GeV) and are delivered to two experimental areas and a neutron irradiation station near the target. This contribution includes a description of the physics and engineering design processes that brought the facility from its second-generation target to its current third-generation target, the planned autopsy of the second-generation target in 2023 to investigate its status after 10 years of operation, tests under beam irradiation carried out on target prototypes at CERN’s HiRadMat facility, and the commissioning with beam of the new target, as well as the challenges encountered during the first year of its operation.
This study introduces numerical advancements in an alternative design for the Super Proton Synchrotron (SPS) Beam Dump Facility (BDF) at the European Laboratory for Particle Physics (CERN). The ...design envisions a high-power operation target made of flowing liquid lead. The proposed BDF is a versatile facility for both beam-dump-like and fixed-target experiments. The target behavior is studied, assuming a proton beam with a momentum of 400 GeV/c, a pulse frequency of 1/7.2 Hz, and an average beam power of 355 kW. Using various Computational Fluid Dynamics (CFD) codes, we evaluate the behavior of liquid lead and predict the thermal stress on the target vessel induced by the pulsed heat source generated by the charged particle beam. The comparison increases the reliability of the results, investigating the dependencies on the CFD modeling approach. The beam is a volumetric heat source with data from the beam-lead interaction simulations provided by the European Laboratory for Particle Physics and obtained with a Monte Carlo code. Velocity field and stress profiles can enhance the design of the lead loop and verify its viability and safety when operated with a liquid metal target.
At the European Laboratory for Particle Physics (CERN), commercial greases and oils are extensively used to lubricate moving devices operating in high-radiation areas, absorbing doses up to the MGy ...range. Due to their sensitivity to radiation, lubricants can become fluid or solid in operation, potentially causing component failures and compromising the operation of the accelerator complex. CERN is therefore developing methodologies to select radiation tolerant commercial lubricants for critical Beam Intercepting Devices (BIDs) such as high-power targets, dumps and collimators. A careful selection of greases is fundamental to reduce the risk of failure, to optimize equipment lifetime and to minimize maintenance and unwanted radiation exposure of personnel in high radiation areas.
Three different parameters are considered to select commercial lubricants: the expected total dose absorbed in operation, the maintenance feasibility and the failure impact in terms of accelerator downtime and of personnel involvement in replacement procedures. Based on these criteria, an example of relevant application is presented: the lubrication of the new internal beam dump of the Super Proton Synchrotron (SPS). Experimental radiation damage data allowed the identification of two radiation tolerant commercial greases to lubricate the dump support jack assembly.
•Commercial lubricants are used in high-radiation areas, where ordinary products fail.•Radiation-tolerant products are identified, to prevent failures in accelerators.•A selection methodology is proposed based on: absorbed dose, maintenance, failure.•The methodology is applied to select greases for an accelerator dump at CERN.•Different irradiation conditions are being investigated to improve the selection.
In an effort to develop and design next generation high power target materials for particle physics research, the possibility of fabricating nonwoven metallic or ceramic nanofibers by electrospinning ...process is explored. A low-cost electrospinning unit is set up for in-house production of various ceramic nanofibers. Yttria-stabilized zirconia nanofibers are successfully fabricated by electrospinning a mixture of zirconium carbonate with high-molecular weight polyvinylpyrrolidone polymer solution. Some of the inherent weaknesses of electrospinning process like thickness of nanofiber mat and slow production rate are overcome by modifying certain parts of electrospinning system and their arrangements to get thicker nanofiber mats of millimeter order at a faster rate. Continuous long nanofibers of about hundred nanometers in diameter are produced and subsequently heat treated to get rid of polymer and allow crystallize zirconia. Specimens were prepared to meet certain minimum physical properties such as thickness, structural integrity, thermal stability, and flexibility. An easy innovative technique based on atomic force microscopy was employed for evaluating mechanical properties of single nanofiber, which were found to be comparable to bulk zirconia. Nanofibers were tested for their high-temperature resistance using an electron beam. It showed resistance to radiation damage when irradiated with 1 MeVKr2++ion. Some zirconia nanofibers were also tested under high-intensity pulsed proton beam and maintained their structural integrity. This study shows for the first time that a ceramic nanofiber has been tested under different beams and irradiation condition to qualify their physical properties for practical use as accelerator targets. Advantages and challenges of such nanofibers as potential future targets over bulk material targets are discussed.
The operation modes for the proposed FCC-ee collider foresee a very small beam spot size and stored beam energies of up to 20.6 MJ in Z production. This necessitates a dedicated beam dumping system. ...To reduce the complexity of the system as well as to minimize the required space, an optimized, semi-passive system has been designed and is presented here. The beam dilution is done with a defocusing triplet structure, followed by passive beam diluter elements (spoilers). This greatly reduces the risk of possible dilution failure scenarios compared to an active dilution kicker-magnet system. The dump core itself is located
∼
70
m
downstream of the spoilers and is designed following the experience gained from the LHC dump.
The dilution performance as well as the interaction effects responsible for the energy deposited in the spoiler, are directly related to the radiation length and the dimension of the device in beam direction. Materials for these spoilers have been studied extensively and key requirements have been identified using both Monte Carlo shower simulations and thermo-mechanical Finite Element Analysis. Even though the maximum temperature reached in the spoilers is well within the working temperature range of the material, the induced mechanical stresses can lead to material failure. Thermo-mechanical simulations have shown that the transversal beam shape plays a key role in the magnitude of mechanical stresses as a result of the beam impact and the abrupt temperature change. This problem is addressed in this paper and an optimized solution is presented.
The HRMT27-RodTarg experiment employed the HiRadMat facility at CERN to impact intense 440 GeV proton beams onto thin rods 8 mm in diameter, 140 mm in length, and made of high-density materials such ...as Ir, W, Ta, Mo, and alloys. The purpose of the experiment was to reduce uncertainties on the CERN antiproton target material response and assess the material selection for its future redesign. The experiment was designed to recreate the extreme conditions reached in the production target, estimated in an increase of temperature above2000°Cin less than0.5μsand a subsequent compressive-to-tensile pressure wave of several gigapascals. The goals of the experiment were (i) to validate the hydrocode calculations used for the prediction of the antiproton target response and (ii) to identify limits and failure mechanisms of the materials of interest. In order to accomplish these objectives, the experiment relied on extensive instrumentation (pointing at the target rod surfaces). This paper presents a detailed description of the experiment as well as the recorded online results which showed that most of the investigated materials suffered internal damage from conditions 5–7 times below the ones present in the AD target. Tantalum, on the other hand, apparently withstood the most extreme conditions without presenting internal cracking.
The neutron Time-Of-Flight (n_TOF) facility at the European Laboratory for Particle Physics (CERN) is a pulsed white-spectrum neutron spallation source producing neutrons for two experimental areas: ...EAR1, located 185 m downstream of the spallation target, and EAR2, located 20 m above the target. The facility is based on a lead target impacted by a high-intensity 20 GeV/c proton beam. It is designed to study neutron-nucleus interactions for neutron kinetic energies from a few meV to several GeV, with applications in nuclear astrophysics, nuclear technology, and medical research. The facility is undergoing a major upgrade in 2019–2020, which will include the installation of the new third-generation target. The second-generation target consists in a water-cooled lead cylinder, while the new target will be cooled by nitrogen to avoid erosion-corrosion phenomena and contamination of the cooling water with radioactive lead spallation products. The new design will be optimized also for the vertical flight path. The operation of the new spallation target will start in 2021. This paper presents an overview on the evolution of the design and on the related R&D activities (including beam irradiation tests) carried out to ensure the best performance for both experimental areas and avoid the contamination issues of the previous targets.
This study presents a further step within the ongoing R&D activities for the redesign of the CERN’s Antiproton Decelerator Production Target (AD-Target). A first scaled target prototype, constituted ...of a sliced core made of ten Ta rods−8mmdiameter, 16 mm length-embedded in a compressed expanded graphite (EG) matrix, inserted in a 44 mm diameter Ti-6Al-4V container, has been built and tested under proton beam impacts at the CERN’s HiRadMat facility, in the so called HRMT-42 experiment. This prototype has been designed following the lessons learned from previous numerical and experimental works (HRMT-27 experiment) aiming at answering the open questions left in these studies. Velocity data recorded on-line at the target periphery during the HRMT-42 experiment is presented, showing features of its dynamic response to proton beam impacts. Furthermore, x-ray and neutron tomographies of the target prototype after irradiation have been performed. These non-destructive techniques show the extensive plastic deformation of the Ta core, but suggest that the EG matrix can adapt to such deformation, which is a positive result. The neutron tomography successfully revealed the internal state of the tantalum core, showing the appearance of voids of several hundreds of micrometers, in particular in the downstream rods of the core. The possible origin of such voids is discussed while future microstructure analysis after the target opening will try to clarify their nature.
The two beam dumps of the Large Hadron Collider (LHC), made up mostly of low-density graphite, are responsible for absorbing the high-energy particle beams when ejected from the accelerator. In the ...frame-work of the project to improve the luminosity in the LHC, the beam intensity will be increased by a factor of around two in the coming years. The dominant load on the dump assembly is the energy deposited in the material by the 7 TeV proton beam. Thermomechanical simulations have to be performed to ensure the safe operation of the dump through assessing the integrity in the future. To date, the particle beam contains an average energy of 370 MJ, which is sent to the dump in a sweep movement within around 80 µs. Based on the large dimensions of the dump core and considering the highly dynamic nature of this load, an explicit code like LS-Dyna® was deemed to be best suited for these studies. This paper presents the methodology proposed to model the discrete time structure of the load, caused by the interaction between the particle beam and the dump. Results of the application of this technique, to determine the temperature, stresses and wave propagation on the downstream wall of this device, are described here. In addition to the methodology of the load application, the results of standard quasi-static material tests on the low-density graphite material in the beam dump are presented, to assess the general nature of the material behavior. These experiments will be the basis for a dynamic test campaign to construct a comprehensive material model, as the graphite used in this device has never been fully characterized under such loading conditions.
Antiprotons are produced at CERN by colliding a 26GeV/c proton beam with a fixed target made of a 3 mm diameter, 55 mm length iridium core. The inherent characteristics of antiproton production ...involve extremely high energy depositions inside the target when impacted by each primary proton beam, making it one of the most dynamically demanding among high energy solid targets in the world, with a rise temperature above 2000°C after each pulse impact and successive dynamic pressure waves of the order of GPa’s. An optimized redesign of the current target is foreseen for the next 20 years of operation. As a first step in the design procedure, this numerical study delves into the fundamental phenomena present in the target material core under proton pulse impact and subsequent pressure wave propagation by the use of hydrocodes. Three major phenomena have been identified, (i) the dominance of a high frequency radial wave which produces destructive compressive-to-tensile pressure response (ii) The existence of end-of-pulse tensile waves and its relevance on the overall response (iii) A reduction of 44% in tensile pressure could be obtained by the use of a high density tantalum cladding.
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