Beam Screen Research Articles

Design Concept for a Future Super Proton-Proton Collider

Following the discovery of the Higgs boson at the LHC in 2012, new large colliders are being considered and studied by the international high-energy community to explore the Higgs boson in details and to probe new physics beyond the Standard Model. In China, a two-stage circular collider project, CEPC-SPPC was proposed and is under study. The first stage, CEPC (Circular Electron Positron Collier, a so-called Higgs factory) is focused on the Higgs physics, and the second stage, SPPC (Super Proton-Proton Collider) will be an energy frontier collider and a discovery machine beyond the LHC. The two colliders will share a same tunnel of 100 km in circumference, with a goal of 250 GeV in center-of-mass for CEPC and 75 TeV for SPPC Phase-I and 125–150 TeV for the SPPC ultimate goal. This article presents the design concept of the SPPC and some study results about the key accelerator physics problems and technical issues, which include luminosity optimization, beam collimation, beam-beam effects, longitudinal beam dynamics, high-field magnets and beam screen.

Evaluation of the nonlinear surface resistance of REBCO coated conductors for their use in the FCC-hh beam screen

To assess the feasibility of using high-temperature superconductors for the beam screens of future circular colliders, we have undertaken a study of the power dependence of the microwave surface resistance in state-of-the-art REBCO coated conductors at about 8 GHz and 50 K. We have employed a dielectric resonator to produce radio-frequency (RF) electromagnetic fields on the surface of the coated conductors having amplitudes similar to those generated by proton bunches circulating in the vacuum chamber of the proposed future circular collider Hadron-Hadron (FCC-hh) at CERN We show that surface resistances in REBCO coated conductors without artificial pinning centers are more affected by a RF magnetic field than those containing nano-inclusions. Despite that, at 8 GHz, 50 K, and 9 T, most REBCO coated conductors studied outperform copper in terms of surface resistance, with the best sample having a 2.3 mΩ surface resistance while being subject to an RF field 2.5 times stronger than that in the FCC-hh. We also extrapolate the measured data to 16 T and 1 GHz, the actual FCC-hh dipole magnetic field, and the mid-beam frequency spectrum, demonstrating the possibility of lowering the surface resistance of the vacuum chamber by up to two orders of magnitude compared to copper. Further, we discuss the correlation between the time structure of the electromagnetic fields provided by vector network analyzers compared to the proton bunches’ time structure in the collider and present the effect of low alternating magnetic fields on vortex displacement and the possibility of demagnetization of superconducting samples.

Photostimulated desorption performance of the future circular hadron collider beam screen

Synchrotron radiation (SR) originated at superconducting bending magnets is known to be at the origin of several beam detrimental effects related to vacuum instabilities. One of the major challenges in the design of the vacuum beam pipes of high-energy hadron colliders is the SR coping strategy. In the case of the future circular hadron collider (FCC-hh), a Cu-coated beam screen (BS) operating in the range of 40--60 K has been designed with the aim of protecting the superconducting magnet cold bores from direct synchrotron irradiation. In order to experimentally study the FCC-hh BS vacuum and cryogenic performance, two sample prototypes were manufactured and installed in the beam screen test-bench experiment (BESTEX) at the Karlsruhe Research Accelerator (KARA) at the Karlsruhe Institute of Technology (KIT). The emitted SR has a critical energy of 6.2 keV, very similar to the 4.6 keV of FCC-hh. Irradiation at both room (RT) and cryogenic (77 K) temperatures showed a significant reduction of the molecular photostimulated desorption yields ($\ensuremath{\eta}$) of the FCC-hh beam screen compared to those of Cu samples. A first approximation of $\ensuremath{\eta}$ and its evolution with the photon dose accumulated on the FCC-hh BS prototype at 77 K allows to estimate that a machine conditioning period of $\ensuremath{\sim}1.2$ months would be needed to reduce the photostimulated molecular density at the necessary levels to ensure a 100 h beam lifetime at nominal FCC-hh operation.

3D Magnetic Field Analysis of LHC Final Focus Quadrupoles with Beam Screen

3D Magnetic Field Analysis of LHC Final Focus Quadrupoles with Beam Screen

Beam-Induced Surface Modification of the LHC Beam Screens: The Reason for the High Heat Load in Some LHC Arcs?

Beam-Induced Surface Modification of the LHC Beam Screens: The Reason for the High Heat Load in Some LHC Arcs?

A Beam Screen to Prepare the RHIC Vacuum Chamber for EIC Hadron Beams: Conceptual Design and Requirements

A Beam Screen to Prepare the RHIC Vacuum Chamber for EIC Hadron Beams: Conceptual Design and Requirements

Mechanical Behavior of the Shielded HL-LHC Beam Screen During a Magnet Quench

In the framework of the High-Luminosity Large Hadron Collider (HL-LHC) project, larger and shielded beam screens will be installed in the beam pipe of the superconducting magnets of the insertion next to the ATLAS and CMS detectors. The beam screen is a complex assembly that guarantees the vacuum requirements while shielding the magnet cold mass from the induced heat loads. Such an assembly has to withstand high intensity electromagnetic forces induced during magnet quenches. The mechanical stability was verified in a dedicated quench test campaign performed at the magnet test station of CERN. Strain gauges, custom-made probes, and optical fibers were installed in the beam screen to measure deformations during a quench. Magnetic field measurements were also carried out by means of pick-up coils mounted within the assembly. The main outcomes of this work are the elastic behaviour of the beam screen after 52 quenches and a satisfactory agreement between measurements and simulations.

Gas density evolution in beam screen of super proton-proton collider

Vacuum stability is one of the key issues in the design of particle accelerators, especially high-energy super proton-proton colliders. The synchrotron radiation generated by proton beams in the bending area will desorb and crack the gas molecules which have adsorbed on the wall of the cold bore. The collision or scattering between the proton beam and the desorbed gas molecules may result in the degradation of the beam quality and the reduction of beam life time, and even the collapse of the beam. Usually a copper coated stainless steel beam screen is installed in the cold bore to intercept synchrotron radiation and reduce gas desorption. Based on the design parameters of the Super Proton-Proton Collider, in this paper the source of gas in the beam screen is analyzed. By considering the photon-induced desorption process and the gas molecule cracking process, the gas dynamic model in the beam screen is established. Moreover, the calculation of the evolution of the gas density in the beam screen with the beam operating time is carried out, and the effect of TiZrV non-evaporable getter film coated beam screen on the dynamic gas density is explored. The results show that H<sub>2</sub> is the main desorption gas in the beam, the next is CO, while the molecular density of CO<sub>2</sub> and CH<sub>4</sub> are limited by molecular cracking. The maximum gas density in the beam screen appears at the initial stage of operation, and the gas density decreases with time going by. In order to strengthen adsorption and reduce desorption, TiZrV coated beam screen is discussed in this paper. In the case of TiZrV coated stainless steel beam screen, the maximum equivalent H<sub>2</sub> density is about two order of magnitude lower than in the case of copper coated stainless steel beam screen. The non-evaporable getter(NEG) for beam screen material can significantly improve vacuum performance. The calculation results can qualitatively reflect the dynamic vacuum evolution in the beam screen during the beam operation and provide a reference for designing vacuum systems.

Thermal-structural coupling analysis of beam screen in super proton-proton collider

High-energy colliders play an indispensable role in particle physics and high-energy physics. Beam screen is one of the key parts in the high-energy collider. It is used to transfer the heat generated by the beam in the pipeline to a cooling system, and absorb the residual gas to the cold bore through the pumping holes on the wall of the beam screen to ensure the vacuum stability at the same time. However, in the process of transferring thermal load, the deformation caused by temperature change will affect the structural stability of the beam screen. How to reduce the deformation as much as possible while ensuring the good heat transfer performance of the beam screen is one of the key issues in optimizing the structural design of the beam screen. In this paper, the heat transfer performance and mechanical property of the beam screen model are simulated and optimized based on the ANSYS simulation results to ensure the normal and stable operation of the beam in the super proton-proton collider. For the inner surface of the outer screen of the beam screen, the method of reducing the thickness of the copper coating is used to reduce the Lorentz force generated during operation. The calculation results from the relevant theoretical models show that when the thickness of the copper coating varies from 0 to 100 μm, the copper coating with a thickness of 75 μm can reduce the maximum deformation of the outer screen of the beam screen by 70.9%, while the maximum temperature of the beam screen can be increased by 1.1%. For the inner screen of the beam screen, a design scheme in which supporting ribs are arranged at intervals is used to reinforce the structure and improve the overall structural stability of the beam screen. The calculation results show that the maximum deformation of the inner screen of the beam screen can be reduced by 86.8% and the maximum temperature of the beam screen is reduced by 7.69%, compared with the case without supporting fins, when the interval between two adjacent supporting fins is 1 pumping hole. The research results provide important theoretical reference for the design of beam screen, which is the key component of the vacuum system of the new-generation high energy particle accelerator.

Stability limits with Landau damping in the FCC-hh

The resistive wall impedance is one of the expected main drivers of transverse beam instabilities in the proposed Future Circular Collider hadron-hadron option (FCC-hh). We obtain the resistive wall impedance for the FCC-hh beam screen from a two-dimensional finite element solver. The impedances and resulting growth rates are compared to the LHC, using similar models for the resistivity of the copper layer. Similar to the LHC and in addition to active feedback, dedicated octupole magnets together with a finite chromaticity should be employed for Landau damping, as a cure against transverse beam instabilities. The stability boundary provided by an LHC-like octupoles configuration in combination with an electron lens is obtained from a dispersion relation including the two-dimensional tune spreads. The prediction from the simple dispersion relation are compared to the corresponding beam transfer function and to the stability boundaries reconstructed using particle tracking with an effective impedance. The electron cloud induced tune spreads and their scaling with higher energy and smaller beam pipe radius are estimated. Besides the important estimation of growth rates and stability threshold for FCC-hh we also try to improve the understanding of the scaling of coherent instabilities and their thresholds with energy towards a possible highest-collider limit, using the example of two high-energy colliders, the existing LHC and the proposed FCC-hh.

Dynamic simulations of the HL-LHC cryogenic system during beam operation

This paper presents a set of dynamic simulations performed on the future High Luminosity Large Hadron Collider (HL-LHC) cryogenic system. The objectives of these simulations are to provide main pressure, temperature and flow transients over the cryogenic distribution system around the collision points 1 and 5 during the forecast beam operation. These simulations serve the different cryogenic system specifications where strong dynamic heat loads will induce significant transient modes. This dynamic model embeds the 1.9K cooling loops (inner triplets, D1-D2 magnets and crab cavities), the beam screen cooling loops between 60K and 80K or between 4.5K and 20K and the cryogenic distribution line. As result, a series of recommendations is given to mitigate sufficiently the transients such as the use of significant preloading of magnets in association with feed-forward controls.

Energy-resolved secondary-electron emission of candidate beam screen materials for electron cloud mitigation at the Large Hadron Collider

Energy-resolved secondary electron spectroscopy has been performed on air-exposed standard Cu samples and modified Cu surfaces that are tested and possibly applied to efficiently suppress electron cloud formation in the high-luminosity upgrade of the Large Hadron Collider at CERN. The Cu samples comprise pristine oxygen-free, carbon-coated and laser-structured surfaces, which were characterized prior to and after electron irradiation and rare-gas ion bombardment. Secondary-electron and reflected-electron yields measured with low charge dose of the samples exhibit a universal dependence on the energy of the primary impinging electrons. State-of-the-art models can successfully be used to describe the spectroscopic data. The supplied spectral dependence of electron emission and integrated electron yield as well as the derived parametrization can serve as a basis for forthcoming simulations of electron cloud formation and multipacting.

Total Body Irradiation as Conditioning Regimen for Haematopoietic Progenitor Cell Transplant: A Case Report and Literature Review

This case study presents a young adult man with lymphoblastic leukaemia B who required total body irradiation (TBI) as a conditioning regimen for haematopoietic progenitor cell transplant (HPT) as the only curative treatment option for his oncological disease. TBI was carried out with personalised patient immobilisation, three-dimensional simulation, radiophysical planning and dosimetric calculations. A total of 12 Gy were prescribed to be administered twice a day for 3 days in a row by means of volumetric modulated intensity radiotherapy with several isocentres. The best technique for the administration of this radiotherapy is discussed because, although the clinical efficacy of the administration of this body dose has been well known for decades, technological advances have brought us new possibilities when compared to the traditional TBI (bilateral with horizontal photon beam and absorbent screen). These advances include the technique used in this case (multi-isocentre volumetric-radiotherapy), which allows a better doses distribution, reducing the dose in organs at risk (OARs) and producing less toxicity, and therefore allowing the inclusion of patients who would not tolerate a conventional TBI. In addition, this method would allow the dose to be scaled up locally in higher areas at risk with better results in the disease control.

High frequency response of thick REBCO coated conductors in the framework of the FCC study

A thorough microwave response study of high temperature superconductors, considered as an alternative beam screen coating, has become integral in the design decisions for CERN’s future research infrastructure. Here, we present the surface resistance R_{s} of various text {REBa}_{2}text {Cu}_{3}text {O}_{7-x} (RE = rare earth) coated conductors available in large scale as a function of magnetic field in a broad temperature range measured by a Hakki–Coleman type resonator with resonant frequency nu approx {8},{text {GHz}}. Analysis of the high frequency dissipation supported by DC transport characterization reveals the vortex dynamics in thick text {REBa}_{2}text {Cu}_{3}text {O}_{7-x} films. Determined microscopic vortex parameters span over a wide range of magnitudes and reflect the relevance of the superconducting layer’s microstructure. We demonstrate that the depinning frequencies nu _0 surpass nu, which confirms the operation in high performing, low dissipation pinning regime at measurement conditions. Surface impedance extrapolation to FCC-hh conditions points towards a significant outperformance of copper by coated conductors in terms of surface resistance. The surface resistance margins would open up potential ways for a more efficient frontier circular collider.

Helical beam screen for the Future Circular Collider for hadrons injection kicker magnets

The Future Circular Collider for hadrons (FCC-hh) is the proposed high-energy frontier particle collider, which is expected to enable proton-proton collisions at a center-of-mass energy of 100 TeV. The specifications for the FCC-hh injection kicker system are very challenging. To provide fast magnetic field rise and fall times, and low ripple during the flat-top, ferrite loaded transmission line type magnets will be used. To limit the beam coupling impedance, a suitable beam screen will be placed in the aperture of each kicker magnet. Due to issues associated with the ``conventional'' beam screen design, used in the injection kickers magnets of the Large Hadron Collider (LHC), such as high voltage (HV) breakdowns and yoke heating problems, we have developed a novel concept of a helical beam screen. The fundamental advantage of the new design, in comparison to the conventional beam screen, is a significant reduction of the maximum voltage induced on the screen conductors, thus a greatly reduced probability of an electrical breakdown of the beam screen. In addition, the longitudinal beam coupling impedance of the helical beam screen is optimized to reduce power deposition in the kicker magnet. Furthermore, the helical beam screen allows a reduction of the maximum transverse beam coupling impedance of the kicker system. Detailed numerical simulations, theoretical studies and experimental results demonstrate that a new design is a promising solution not only for the FCC-hh, but also for existing machines.

Future Circular Collider beam screen: progress on Tl-1223 HTS coating

Thallium-1223, a superconductor with high critical temperature (Tc ∼ 120 K) and high irreversibility line is a promising alternative to copper layers as a low surface impedance material in particle accelerator components. In the existing design of the Future Circular Collider (FCC-hh), for reasons of cryogenic efficiency and vacuum stability, the beam screen that shields the dipoles from synchrotron radiation has to stay at best in the temperature range between 40 and 60 K, in which copper surface resistance might be too high to prevent beam instabilities due to wakefields. This paper reports the progress on the realization of thallium-1223 based high temperature superconducting (HTS) coatings realized by electrochemical deposition. The study of the Tl-1223 phase has been carried out on precursor-pellets and films. Transport characterization revealing a very high irreversibility line and also high local critical currents obtained from Scanning Hall Probe Microscopy (SHPM) measurements will be shown. A first analysis of compatibility in vacuum has been carried out and the generation of secondary electrons (SEY) has been investigated as well.The encouraging results, although not conclusive, will state that thallium-based phase could be suitable for the proposed application.

Preliminary conceptual design of FCC-hh cryo-refrigerators: Air Liquide Study

In the framework of a world-wide international collaboration, the FCC-hh, a 100 TeV hadron collider in a 100-km long tunnel, is proposed as a future circular collider beyond LHC at CERN offering the broadest discovery potential at the energy frontier. For such high performance hadron collider, the cryogenic system has to distribute very large cooling capacities all along the 100-km tunnel for the superconducting magnets continuously cooled at 1.9 K and for the beam screens operated between 40 and 60 K. The required total cooling power will be produced in 10 refrigeration plants with a unit equivalent capacity of 100 kW at 4.5 K, up to 4 times larger than the present state-of-the-art. Half of the entropic refrigeration load is due to the synchrotron radiation produced by the high-energy proton beams and deposited on beam screens actively cooled around 50 K. This non-conventional thermal load distribution is an additional challenge for the FCC-hh cryogenic system. Furthermore, the cryogenic system has to cool down the cold mass of the FCC-hh machine in less than 20 days with controlled thermal gradients in the cryo-magnets and beam screens. Based on preliminary design works from research institutes, an engineering study was performed with world-leader industries to assess a preliminary conceptual design for the FCC-hh cryogenic plants with industrial solutions and innovative technologies. The present paper recalls the FCC-hh cryogenic requirements and presents the main results of Air Liquide study confirming the novel precooling refrigeration option down to 40 K.

Cryogenic management of the LHC run 2 dynamic heat loads

During the LHC (Large Hadron Collider) Run 2 between 2015 and 2018 inclusive, significant dynamic heat loads have been generated and successfully managed by the LHC cryogenic system. These dynamic heat loads are generated by several physical phenomena occurring at two temperature levels and with different time constants. On the magnet cold-mass maintained at 1.9 K, dynamic heat loads are coming from eddy currents generated during the magnet transients, resistive heating in welds of superconducting electrical circuits, beam gas scattering, beam losses, and secondary particles escaping from collisions (debris). On the beam screens, actively cooled between 4.6 K and 20 K, the circulating beams produce also dynamic heat loads due to synchrotron radiations, image current and photo-electron clouds. This paper presents the measurements inventory performed during the Run 2 to assess these dynamic heat loads as a function of the different accelerator parameters (beam energy, beam intensity, injection scheme, etc.). Then, the related compensation measures and adapted cryogenic operation modes applied to manage the induced transients at the different time scales will be presented.

Thermodynamic and economic aspects of the Nelium Turbo-Brayton refrigerator development for the FCC-hh

Within the conceptual design study for the Future Circular Hadron Collider (FCC-hh) it was shown, that a large part of the total cryogenic heat load falls into the temperature range between 40 to 60 K. Thus, additional cryogenic refrigerators for this temperature level are specified for each of the 10 foreseen cryoplants. Such a cryogenic system was developed at the TU Dresden and is based on a Brayton cycle working with a neon-helium mixture as refrigerant and using multistage centrifugal compressors. The duty requirements comprise a 6.2 MW total heat load at 40 to 60 K for beam screens and shielding, additional 2.7 MW at 300 to 40 K for the pre-cooling of the helium cycle and a turndown ratio of up to 3.8. The optimisation of the referenced system was performed in order to obtain a high efficiency of the cryogenic cycle and tolerable costs for system components at the same time. An analysis of the mixture composition influence on the components and on the total gas mass was performed. Restrictions for industrially existing hardware were taken into consideration. Updated cycle parameters are subsequently described.

New spiral beam screen design for the FCC-hh injection kicker magnet

The injection kicker system for the Future Circular Collider (FCC-hh) must satisfy demanding requirements. To achieve low pulse ripple and fast field rise and fall times, the injection system will use ferrite loaded transmission line type magnets. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, interaction of the high intensity beam with the real part of the longitudinal beam coupling impedance can result in high power deposition in the ferrite yoke. This gives a significant risk that the ferrite yoke will exceed its Curie temperature: hence, a suitable beam screen will be a critical feature. In this paper, we present a novel concept - a spiral beam screen. The fundamental advantage of the new design is a significant reduction of the maximum voltage induced on the screen conductors, thus decreased probability of electrical breakdown. In addition, the longitudinal beam coupling impedance is optimized to minimize power deposition in the magnet.