Adaptive Collimator Design for Future Particle Accelerators

The function of collimators in the LHC is to control and safely dispose of the halo particles that are produced by unavoidable beam losses from the circulating beam. Even tiny proportions of the 7TeV beam have the stored energy to quench the superconducting magnets or damage parts of the accelerator if left unchecked. Particle absorbing Low-Z material make up the active area of the collimator (jaws). Various beam impact scenarios can induce significant temperature gradients that cause deformation of the jaws. This can lead to a reduction in beam cleaning efficiency which can have a detrimental effect on beam dynamics. This has led to research into a new Adaptive collimation system (ACS). The ACS is a re-design of a current collimator already in use at CERN. The ACS will incorporate a novel fibre based measurement system and piezoceramic actuators mounted within the body of the collimator to maintain jaw straightness below the 100µm specification. These two systems working in tandem can monitor, and correct for, the jaw structural deformation for all impact events. This paper details the concept and technical solutions of the ACS as well as preliminary validation calculations

Beam Coupling Impedance of the LHC TCTP Collimators

As part of an upgrade to the LHC collimation system, 8 TCTP and 1 TCSG collimators are proposed to replace existing collimators in the collimation system. In an effort to review all equipment placed in the accelerator complex for potential side effects due to collective effects and beam-equipment interactions, beam coupling impedance simulations are carried out in both the time-domain and frequency-domain of the full TCTP design. Particular attention is paid to trapped modes that may induce beam instabilities and beam-induced heating due to cavity modes of the device.As part of an upgrade to the LHC collimation system, 8 TCTP and 1 TCSG collimators are proposed to replace existing collimators in the collimation system. In an effort to review all equipment placed in the accelerator complex for potential side effects due to collective effects and beam-equipment interactions, beam coupling impedance simulations are carried out in both the time-domain and frequency-domain of the full TCTP design. Particular attention is paid to trapped modes that may induce beam instabilities and beam-induced heating due to cavity modes of the device

The HRMT27 (Rodtarg) Experiment: Design, Operation and First Results

The HRMT27-Rodtarg- experiment used the HiRadMat facility at CERN to impact intense 440 GeV proton beams onto thin rods - 8 mm diameter, 140 length - made of high-density materials such as Ir, W, Ta, Mo among others. 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 target, estimated as an increase of temperature above 2000 ºC in less than 0.5 µs and a subsequent compressive-to-tensile pressure wave of several GPa. This document includes a detailed summary of the experimental setup and online recorded data. Results suggest that all the irradiated materials except tantalum suffered internal damage from conditions 5-7 lower than those reached in the AD-Target, while tantalum targets clearly showed the best dynamic response, remaining un-cracked during the experiment. Foreseen post irradiation examinations will complete this study

Integration of the 11-T Nb3_{3}Sn Dipoles and Collimators in the LHC

The Large Hadron Collider (LHC) collimation system upgrade plan comprises new collimators in the dispersion suppressors. The length required for each collimator along the LHC lattice is obtained by replacing an LHC main dipole and its cryostat with two shorter but stronger 11-T Nb_3Sn magnets keeping the equivalent integrated field of the dipole removed. This requires a modification of the continuous cryostat, in order to create room-temperature beam vacuum sectors for the integration of the new collimators. In this paper, we present a new cryostat designed to allow the installation of a collimator between the 11-T magnets, while ensuring the continuity of the cryogenics, vacuum, and magnet powering systems of the LHC continuous cryostat. Challenging constraints, in terms of fabrication, alignment, and space, led to the development of a cryostat composed of three independent modules. Two of the modules house the 11-T dipole cold masses, which are cooled in the same 1.9-K pressurized superfluid helium bath of the main dipoles. These make use of the same design features of the LHC magnet cryostats, in order to contain construction and assembly costs and benefit from well-established procedures. A third module, which is placed between the two magnets, is equipped with cold to warm transitions on the beam lines and creates the space for the collimator between the vacuum vessel of the two 11-T magnet cryostats. The main functionalities, requirements, and implemented design solutions for this new cryostat are presented and discussed, in the context of the challenging integration in the LHC continuous cryostat and its tunnel

Experiment exposing refractory metals to impacts of 440 GeV/c proton beams for the future design of the CERN antiproton production target: Experiment design and online results

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 above 2000 °C in less than 0.5  μs and 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

Upgrade of the TCDQ Diluters for the LHC Beam Dump System

The TCDQ diluters are installed as part of the LHC beam dump system to protect the Q4 quadrupole and other downstream elements during a beam dump that is not synchronised with the abort gap, or in case of erratic firing of the extraction kickers. These diluter elements installed during Run 1 were compatible with beam up to 60 % of the nominal intensity, which was insufficient for the second run of the LHC. This paper describes the requirements for the upgrade done during the First Long Shutdown (LS1), to make the TCDQ compatible with the full 7 TeV LHC beam at intensities required for the future runs of the machine. Subsequently the mechanical design changes, implementation and commissioning of the TCDQ are reported

Design of a cloverleaf-racetrack dipole demonstrator magnet with dual ReBCO conductor

For future 20+ T accelerator type magnets, ReBCO superconductors are ideal for their high current density in high magnetic field. At CERN, demonstrator dipole magnets using ReBCO conductor are being developed in order to study their feasibility. In this work, a design of a cloverleaf-racetrack magnet is presented, which consist of two poles. A key problem in such magnets is how to realize the coil-ends without causing degradation due to coil winding, cool down and operation. The cloverleaf geometry accommodates the particle beam pipe without any hard-way ReBCO tape bending. To design such geometry of the coil-end, a new method using Bézier splines is presented. The ReBCO coils are wound with dual tape conductor where the ReBCO layers are facing each other. For quench protection, the coils are non-insulated, allowing the coil current at quench to redistribute transversally through the winding pack. A comparison between dry-wound and soldered non-insulated coils is made. Progress on the electromagnetic and mechanical design of the cloverleaf magnet is reported in this paper

The Hiradmat 27 Experiment: Exploring High-Density Materials Response at Extreme Conditions for Antiproton Production

The HRMT27-Rodtarg- experiment used the HiRadMat facility at CERN to impact intense 440 GeV proton beams onto thin rods -8 mm diameter, 140 length- made of high-density materials such as Ir, W, Ta, Mo among others. The purpose of the experiment has been 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 named target, estimated on an increase of temperature above 2000 °C in less than 0.5 μs and a subsequent compressive-to-tensile pressure wave of several GPa. The goals of the experiment were to validate the hydrocode calculations used for the prediction of the antiproton target response and to identify limits and failure mechanisms of the materials of interest. In order to accomplishing these objectives, the experiment counted on extensive online optical instrumentation pointing at the rod surfaces. Online results suggest that most of the targets suffer important internal damage even from conditions seven times lower than the reached in the AD-target. Tantalum targets clearly showed the best dynamic response

Novel Materials for Collimators at LHC and its Upgrades

Collimators for last-generation particle accelerators like the LHC, must be designed to withstand the close interaction with intense and energetic particle beams, safely operating over an extended range of temperatures in harsh environments, while minimizing the perturbing effects, such as instabilities induced by RF impedance, on the circulating beam. The choice of materials for collimator active components is of paramount importance to meet these requirements, which are to become even more demanding with the increase of machine performances expected in future upgrades, such as the High Luminosity LHC (HL-LHC). Consequently, a farreaching R&D program has been launched to develop novel materials with excellent thermal shock resistance and high thermal and electrical conductivity, replacing or complementing materials used for present collimators. Molybdenum Carbide - Graphite and Copper-Diamond composites have been so far identified as the most promising materials. The manufacturing methods, properties and application potential of these composites will be reviewed along with the experimental program which is to test their viability when exposed to high intensity particle beams