The design of a future multi-TeV muon collider needs new ideas to overcome the technological challenges related to muon production, cooling, accumulation and acceleration. In this paper a layout of a positron driven muon source known as the Low EMittance Muon Accelerator (LEMMA) concept is presented. The positron beam, stored in a ring with high energy acceptance and low emittance, is extracted and driven to a multi-target system, to produce muon pairs at threshold. This solution alleviates the issues related to the power deposited and the integrated Peak Energy Density Deposition (PEDD) on the targets. Muons produced in the multi-target system will then be accumulated before acceleration and injection in the collider. A multi-target line lattice has been designed to cope with the focusing of both the positron and muon beams. Studies on the number, material and thickness of the targets have been carried out. A general layout of the overall scheme and a description is presented, as well as plans for future R&D.

Positron driven muon source for a muon collider

Fluidized tungsten powder has been proposed as a potential target technology for particle accelerator applications with very high power highly focused pulsed beams. This has motivated a series of experiments carried out at the HiRadMat facility at CERN to study the response of a tungsten powder sample to an impinging high energy proton beam pulse. The main observation was that of beam induced lifting of the powder sample which was recorded by high speed video. In this paper we consider three mechanisms to explain the observed powder lift including aerodynamic, thermal expansion and induced charge effects. Simulations of the aerodynamic effect revealed that this could not explain the magnitude of the observed eruptions especially during tests carried out with the powder in a vacuum. Thermal expansion of tungsten particles giving rise to the eruption seems implausible due to the propensity for the powder to absorb perturbations. We show that the observations can be explained by a Coulombic eruption of the tungsten particles. The high energy beam leaves a pattern of charge distributed in the poorly conducting powder sample, which creates an electric field that consequently results in a force acting on the individual charged particles. We calculate the charge deposited, the electric field and the resulting acceleration and show that this is a plausible mechanism for causing the observed eruptions. We believe the response of a granular conductive sample to an incident proton beam has not previously been explained.

/pdf/observed-proton-beam-induced-disruption-of-a-tungsten-powder-2rvypnp3ts.pdf

Observed proton beam induced disruption of a tungsten powder sample at CERN

The Beam Dump Facility (BDF) is a project for a new facility at CERN dedicated to high intensity beam dump and fixed target experiments. Currently in its design phase, the first aim of the facility is to search for Light Dark Matter and Hidden Sector models with the Search for Hidden Particles (SHiP) experiment. At the core of the facility sits a dense target/dump, whose function is to absorb safely the 400 GeV/c Super Proton Synchrotron (SPS) beam and to maximize the production of charm and beauty mesons. An average power of 300 kW will be deposited on the target, which will be subjected to unprecedented conditions in terms of temperature, structural loads and irradiation. In order to provide a representative validation of the target design, a prototype target has been designed, manufactured and tested under the SPS fixed-target proton beam during 2018, up to an average beam power of 50 kW, corresponding to 350 kJ per pulse. The present contribution details the target prototype design and experimental setup, as well as a first evaluation of the measurements performed during beam irradiation. The analysis of the collected data suggests that a representative reproduction of the operational conditions of the Beam Dump Facility target was achieved during the prototype tests, which will be complemented by a Post Irradiation Examination campaign during 2020.

Beam impact tests of a prototype target for the Beam Dump Facility at CERN: experimental setup and preliminary analysis of the online results

The ever-expanding requirements of high-power targets and accelerator equipment has highlighted the need for facilities capable of accommodating experiments with a diverse range of objectives. HiRadMat, a High Radiation to Materials testing facility at CERN has, throughout operation, established itself as a global user facility capable of going beyond its initial design goals. Pulsed high energy, high intensity, proton beams have been delivered to experiments ranging from materials testing, detector’s prototype validation, radiation to electronics assessment and beam instrumentation. A 440 GeV/c proton beam is provided directly from the CERN SPS. Up to 288 bunches/pulse at a maximum pulse intensity of 3.5 × 10 protons/pulse can be delivered. Through collaborative efforts, HiRadMat has developed into a state-of-the-art facility with improved in situ measurement routines, beam diagnostic systems and data acquisition techniques, offered to all users. This contribution summarises the recent experimental achievements, highlights previous facility enhancements and discusses potential future upgrades with particular focus on HiRadMat as a facility open to novel experiments.

HiRadMat: A Facility Beyond the Realms of Materials Testing

Beam impact tests of a prototype target for the beam dump facility at CERN: Experimental setup and preliminary analysis of the online results

Beryllium is extensively used in various accelerator beam lines and target facilities as a material for beamwindows, and to a lesser extent, as secondary particle production targets. With increasing beam intensities of future accelerator facilities, it is critical to understand the response of beryllium under extreme conditions to reliably operate these components as well as avoid compromising particle production efficiency by limiting beam parameters. As a result, an exploratory experiment at CERN’s HiRadMat facility was carried out to take advantage of the test facility’s tunable high intensity proton beam to probe and investigate the damage mechanisms of several beryllium grades. The test matrix consisted of multiple arrays of thin discs of varying thicknesses as well as cylinders, each exposed to increasing beam intensities. This paper outlines the experimental measurements, as well as findings from Post-Irradiation-Examination (PIE) work where different imaging techniques were used to analyze and compare surface evolution and microstructural response of the test matrix specimens.

Experimental results of beryllium exposed to intense high energy proton beam pulses

This paper reports the results from single-pulse experiments of a $440\text{ }\text{ }\mathrm{GeV}/c$ proton beam interacting with granular tungsten samples in both vacuum and helium environments. Remote high-speed photography and laser Doppler vibrometry were used to observe the effect of the beam on the sample grains. The majority of the results were derived from a trough containing $\ensuremath{\sim}45\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ diameter spheres (not compacted) reset between experiments to maintain the same initial conditions. Experiments were also carried out on other open and contained samples for the purposes of comparison both with the $45\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ grain results and with a previous experiment carried out with sub-$250\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ mixed crystalline tungsten powder in helium [Phys. Rev. ST Accel. Beams 17, 101005 (2014)]. The experiments demonstrate that a greater dynamic response is produced in a vacuum than in a helium environment and in smaller grains compared with larger grains. The examination of the dynamics of the grains after a beam impact leads to the hypothesis that the grain response is primarily the result of a charge interaction of the proton beam with the granular medium.

Proton beam induced dynamics of tungsten granules

Beryllium is a material extensively used in various particle accelerator beam lines and target facilities, as beam windows and, to a lesser extent, as secondary particle production targets. With increasing beam intensities of future multimegawatt accelerator facilities, these components will have to withstand even greater thermal and mechanical loads during operation. As a result, it is critical to understand the beam-induced thermal shock limit of beryllium to help reliably operate these components without having to compromise particle production efficiency by limiting beam parameters. As part of the RaDIATE (radiation damage in accelerator target environments) Collaboration, an exploratory experiment to probe and investigate the thermomechanical response of several candidate beryllium grades was carried out at CERN's HiRadMat facility, a user facility capable of delivering very-high-intensity proton beams to test accelerator components. Multiple arrays of thin beryllium disks of varying thicknesses and grades, as well as thicker cylinders, were exposed to increasing beam intensities to help identify any thermal shock failure threshold. Real-time experimental measurements and postirradiation examination studies provided data to compare the response of the various beryllium grades, as well as benchmark a recently developed beryllium Johnson-Cook strength model.

Thermal shock experiment of beryllium exposed to intense high energy proton beam pulses

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Experimental results of beryllium exposed to intense high energy proton beam pulses

Proton beam induced dynamics of tungsten granules

Thermal shock experiment of beryllium exposed to intense high energy proton beam pulses