[en] To reach the required luminosity at the CLIC interaction point, about 2000 quadrupoles along each linear collider are needed to obtain a vertical beam size of 1 nm at the interaction point. Active mechanical stabilization is required to limit the vibrations of the magnetic axis to the nanometer level in a frequency range from 1 to 100 Hz. The approach of a stiff actuator support was chosen to isolate from ground motion and technical vibrations acting directly on the quadrupoles. The actuators can also reposition the quadrupoles between beam pulses with nanometer resolution. A first conceptual design of the active stabilization and nano positioning based on the stiff support and seismometers was validated in models and experimentally demonstrated on test benches. Lessons learnt from the test benches and information from integrated luminosity simulations using measured stabilization transfer functions lead to improvements of the actuating support, the sensors used and the system controller. The controller electronics were customized to improve performance and to reduce cost, size and power consumption. The outcome of this study has been implemented in the design of the first prototype of a stabilized CLIC quadrupole magnet. (authors)

[en] Two new absorbing materials were developed as collimator inserts to fulfil the requirements of HL-LHC higher brightness beams: molybdenum-carbide graphite (MoGr) and copper-diamond (CuCD). These materials were tested under intense beam impacts at CERN HiRadMat facility in 2015, when full jaw prototypes were irradiated. Additional tests in HiRadMat were performed in 2017 on another series of material samples, including also improved grades of MoGr and CuCD, and different coating solutions. This paper summarizes the main results of the two experiments, with a main focus on the behaviour of the novel composite blocks, the metallic housing, as well as the cooling circuit. The experimental campaign confirmed the final choice for the materials and the design solutions for HL-LHC collimators, and constituted a unique chance of benchmarking numerical models. In particular, the tests validated the selection of MoGr for primary and secondary collimators, and CuCD as a valid solution for robust tertiary collimators. (paper)

[en] To reach a sufficient luminosity, the transverse beam sizes and emittances in future linear particle accelerators should be reduced to the nanometer level. Mechanical stabilisation of the quadrupole magnets is of the utmost importance for this. The piezo actuators used for this purpose can also be used to make fast incremental orientation adjustments with a nanometer resolution. The main requirements for the CLIC stabilisation electronics is a robust, low noise, low delay, high accuracy and resolution, low band and radiation resistant feedback control loop. Due to the high number of controllers (about 4000) a cost optimization should also be made. Different architectures are evaluated for a magnet stabilisation prototype, including the sensors type and configuration, partition between software and hardware for control algorithms, and optimization of the ADC/DAC converters. The controllers will be distributed along the 50 km long accelerator and a communication bus should allow external control. Furthermore, one might allow for an adaptive method to increase the S/N ratio of vibration measurements by combining seismometer measurements of adjacent magnets. Finally a list of open topics, the current limitations and the plans to overcome them will be presented.

[en] Mechanical testing of materials at low temperatures is one of the cornerstones of the Mechanical and Materials Engineering (MME) group at CERN. A long tradition of more than 20 years and a unique know - how of such tests has been developed with an 18 kN double-walled cryostat. Large campaigns of material qualification have been carried out and the mechanical behaviour of materials at 4 K has been vastly studied in sub - size samples for projects like LEP, LHC and its experiments. With the aim of assessing the mechanical properties of materials of higher strength and/or issued from heavy gauge products for which testing standardized specimens of larger cross section might be more adapted, a new 100 kN cryostat capable of hosting different shapes of normalized samples has been carefully designed and fabricated inhouse together with the associated tooling and measurement instrumentation. It has been conceived to be able to adapt to different test frames both dynamic and static, which will be of paramount importance for future studies of fracture mechanics at low temperatures.The cryostat features a double-walled vessel consisting of a central cylindrical section with a convex lower end and a flat top end closure. The transmission of the load is guaranteed by a 4 column system and its precise monitoring is assured by an internal load cell positioned next to the sample in the load train. This innovative approach will be discussed together with other nonconventional instrumentation solutions.A validation of the whole system has been carried out, where bending efforts on instrumented samples have been measured. Additionally, dedicated tooling has been fabricated for the device's optimization. The preliminary results obtained confirm an excellent performance of the system and enhance the analysis of materials under extreme conditions with state of the art instrumentation. (paper)

[en] In order to achieve the required levels of luminosity in the CLIC linear collider, mechanical stabilization of quadrupoles to the nanometre level is required. The paper describes a design of hybrid electronics combining an analogue controller and digital communication with the main machine controller. The choice of local analogue control ensures the required low latency while still keeping sufficiently low noise level. Furthermore, it reduces the power consumption, rack space and cost. Sensitivity to radiation single events upsets is reduced compared to a digital controller. The digital part is required for fine tuning and real time monitoring via digitization of critical parameters.

[en] The future Compact LInear particle Collider (CLIC) under study at CERN will require to stabilize heavy electromagnets, and also to provide them some positioning capabilities. Firstly, this paper presents the concept adopted to address both requirements. Secondly, the control strategy adopted for the stabilization is studied numerically, showing that the quadrupole can be stabilized in both lateral and vertical direction. Finally, the strategy is validated experimentally on a single degree of freedom scaled test bench.

[en] This paper presents an experimental validation of a control strategy capable of both stabilizing and positioning the heavy electromagnets of future particle colliders. The originality of the approach is to use the same active mounts to perform both tasks, with a nanometer precision. In a previous paper, the concept has been studied numerically, and validated on a scaled single degree of freedom (d.o.f.) test bench. In this paper, it is extended to a two d.o.f. test bench, constituted of a heavy mass mounted on two active legs. Firstly, the model is described and the performances are discussed numerically. Secondly, experimental results are presented, and found to correlate well with the model, and comply with the requirements. Finally, the experimental results are combined with a simplified model of the beam-based feedback to evaluate the jitter of the beam. It is found that, at the scale of a single quadrupole, the mechanical stabilization of the quadrupoles reduces the vertical beam jitter by a factor 10.

[en] The increase of the stored beam energy in future particle accelerators, such as the HL-LHC and the FCC, calls for a radical upgrade in the design, materials and instrumentation of Beam Intercepting Devices (BID), such as collimators Following successful tests in 2015 that validated new composite materials and a novel jaw design conceived for the HL-LHC collimators, a new HiRadMat experiment, named “HRMT36-MultiMat”, is scheduled for autumn 2017. Its objective is to determine the behaviour under high intensity proton beams of a broad range of materials relevant for collimators and beam intercepting devices, thin-film coatings and advanced equipment. The test bench features 16 separate target stations, each hosting various specimens, allowing the exploration of complex phenomena such as dynamic strength, internal damping, nonlinearities due to anisotropic inelasticity and inhomogeneity, effects of energy deposition and radiation on coatings. This paper details the main technical solutions and engineering calculations for the design of the test bench and of the specimens, the candidate target materials and the instrumentation system. (paper)

[en] For the Large Hadron Collider luminosity upgrade, two of the NbTi 8.3 T main bending dipoles will be replaced by two shorter Nb₃Sn 11.2 T dipoles to create space for the installation of collimators in the dispersion suppression region. With the aim to verify the design features, several 2 m long 11 T models have been constructed and tested at CERN. During the fabrication and assembly of, so far, seven single and two double aperture short model magnets, several challenges were identified and tackled. These include reproducibility in coil fabrication and assembly procedure, as well as control of mechanical stresses in the conductor and surrounding structure. In order to limit coil over-compression and improve reproducibility, the cable insulation was re-optimized. In addition, a review of the collaring procedure of the 11 T magnet was launched with the goal of reducing the risk of conductor degradation due to excessive stress. In this paper, the main fabrication and assembly steps are described, including the description of the actions taken to resolve the identified weakness. (paper)

[en] Beam Intercepting Devices (BID) are designed to operate in a harsh radioactive environment and are highly loaded from a thermo-structural point of view. Moreover, modern particle accelerators, storing unprecedented energy, may be exposed to severe accidental events triggered by direct beam impacts. In this context, impulse has been given to the development of novel materials for advanced thermal management with high thermal shock resistance like metal-diamond and metal-graphite composites on top of refractory metals such as molybdenum, tungsten and copper alloys. This paper presents the results of a first-of-its-kind experiment which exploited 440 GeV proton beams at different intensities to impact samples of the aforementioned materials. Effects of thermally induced shockwaves were acquired via high speed acquisition system including strain gauges, laser Doppler vibrometer and high speed camera. Preliminary information of beam induced damages on materials were also collected. State-of-the-art hydrodynamic codes (like Autodyn®), relying on complex material models including equation of state (EOS), strength and failure models, have been used for the simulation of the experiment. Preliminary results confirm the effectiveness and reliability of these numerical methods when material constitutive models are completely available (W and Cu alloys). For novel composite materials a reverse engineering approach will be used to build appropriate constitutive models, thus allowing a realistic representation of these complex phenomena. These results are of paramount importance for understanding and predicting the response of novel advanced composites to beam impacts in modern particle accelerators