Federico Carra

LIMITS FOR BEAM INDUCED DAMAGE: RECKLESS OR TOO CAUTIOUS?

Accidental events implying direct beam impacts on collimators are of the utmost importance as they may lead to serious limitations of the overall LHC Performance. In order to assess damage threshold of components impacted by high energy density beams, entailing changes of phase and extreme pressures, state-of-the-art numerical simulation methods are required. In this paper, a review of the different dynamic response regimes induced by particle beams is given along with an indication of the most suited tools to treat each regime. Particular attention is paid to the most critical case, that of shock waves, for which standard Finite Element codes are totally unfit. A novel category of numerical tools, named Hydrocodes, has been adapted and used to analyse the consequences of an asynchronous beam abort on Phase 1 Tertiary Collimators (TCT). A number of simulations has been carried out with varying beam energy, number of bunches and bunch sizes allowing to identify different damage levels for the TCT up to catastrophic failure.

Construction of the CERN Fast Cycled Superconducting Dipole Magnet Prototype

CERN is pursuing a small scale R&D on a fast cycled superconducting dipole magnet (FCM) of interest for the upgrade plan of the LHC accelerator complex. The FCM dipole prototype being built has a number of novel features if compared to other magnets for similar applications. In this paper we describe the magnet design, and its expected performance, focusing especially on the novel features (magnetic circuit, mechanical supports, cooling) and on the details of the manufacturing procedure (coil winding and impregnation, joints, instrumentation and quench protection).

Behaviour of advanced materials impacted by high energy particle beams

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.

The crab cavities cryomodule for SPS test

RF Crab Cavities are an essential part of the HL-LHC upgrade. Two concepts of such systems are being developed: the Double Quarter Wave (DQW) and the RF Dipole (RFD). A cryomodule with two DQW cavities is in advanced fabrication stage for the tests with protons in the SPS. The cavities must be operated at 2 K, without excessive heat loads, in a low magnetic environment and in compliance with CERN safety guidelines on pressure and vacuum systems. A large set of components, such as a thermal shield, a two layers magnetic shield, RF lines, helium tank and tuner are required for the successful and safe operation of the cavities. The sum of all these components with the cavities and their couplers forms the cryomodule. An overview of the design and fabrication strategy of this cryomodule is presented. The main components are described along with the present status of cavity fabrication and processing and cryomodule assembly. The lesson learned from the prototypes and first manufactured systems are also included.

Innovative MoC – graphite composite for thermal management and thermal shock applications

Innovative collimators are being investigated to handle the high energy particle beams foreseen in future upgrades of CERN Large Hadron Collider (LHC). This calls for the development of novel advanced materials, as no existing metal- or carbon-based material possesses the combination of physical, thermal, electrical and mechanical properties, imposed by extreme collimators working conditions. An ambitious research program has been undertaken at CERN and collaborating partners to investigate, process and characterize novel composite materials. A promising new family of materials has been identified in metal/ceramiccarbon composites: these are intended to combine optimum mechanical, thermal and electrical properties, such as mechanical strength, melting temperature, thermal shock resistance, electrical conductivity, and energy absorption. Besides High Energy Physics equipment, these materials are of particular interest for thermal management applications such as high power density electronic packaging, aerospace, automotive, nuclear fusion and solar energy. With that in mind, this paper aims at discussing the properties of investigated materials with respect to their relevance for the various application domains.

Investigation of Dynamic Fracture Behavior of Graphite

The strain-rate sensitivity of brittle materials, such as glass, ceramics or concrete-like materials, is usually easier to be performed in compression. However, also the tensile behavior, which affects phenomena such as spalling, scabbing and fragmentation, has to be investigated to achieve an exhaustive characterization. In last decades, a lot of researchers suggested spalling test as one of the best ways to characterize dynamically brittle materials. This type of test is based on propagation and reflection of elastic waves: the fracture for spalling occurs when, in the material, the tensile stress state, obtained by the reflection on a free surface of a compressive pulse, exceeds the strength limit. These conditions are usually reached using a SHPB setup: a striker bar is launched against the input bar, which is in contact with a long bar specimen free at the opposite surface. In this work, the spalling test has been performed to investigate the dynamic tensile behavior of graphite. The apparatus is actuated by a pneumatic gas-gun (1.5 m long). Striker and input bars are made of high-strength steel 10 mm of diameter. Different striker lengths are used (100 and 80 mm) to obtain different pulse lengths and amplitudes. The input bar is 3.4 m long and is instrumented in the middle. The specimens are 200 mm long and 10 mm of diameter, instrumented at 80 from the free surface with strain-gages.