Main Quadrupole Research Articles

The upgraded quench protection system for main quadrupoles in the LHC

The protection of superconducting magnets is a very important issue and demanding challenge in the LHC and other superconducting accelerating facilities. The quench phenomenon can destroy components of the accelerator, and therefore this digital system was designed, implemented, tested, and installed near each superconducting magnet in the LHC tunnel. The quench detection principle relies on the extraction of resistive voltage by compensation of the inductive part of the voltage. This article presents briefly the architecture applied to the design and the validation of the FPGA-based quench detector for the main quadrupoles of the LHC. The article focusses on digital design with the use of FPGA by VHDL coding and on the verification by simulation. The design is a replacement for the old detection system.

Multispectral plasmonic biosensors based on a Penta-supercell metamaterial for detection of prostate-specific antigen: Ultrasensitive in LC resonance mode

Here, the detection of prostate-specific antigen (PSA) was done using a refractive index sensor based on a plasmonic Penta-supercells metamaterial array. The proposed Penta-supercells metamaterial array consists of four split ring-shaped supercells and a multiplication-shaped supercell in the middle. The results were validated using the three-dimensional Finite-difference time-domain (FDTD) numerical method. The detection of low-concentration biomolecules is a typical drawback of conventional plasmonic biosensors. Our designed Penta-supercells shape biosensor benefits from an ultra-sensitivity. In our designed biosensor, simultaneous excitations of three main plasmon (inductance–capacitance (LC), quadrupole, and dipole) modes can occur, and the LC mode shows a superior sensitivity. The structure was designed optimally, and three different types of metals (Au, Ag, and Al) were examined. LC mode appeiers in Ag and Au and this mode is not seen in Al. Also, the results of this study show the superiority of Ag to Au and Al. Based on the results of this study, the proposed structure achieves a record high sensitivity of 2256 nm/RIU in LC mode and high sensitivity of 1022 nm/RIU in quadrupole mode, and 494 nm/RIU in dipole mode. As another result, the proposed structure is insensitive to orthogonal polarization. The full utilization of these three resonance plasmon modes shows bright prospects for multi-spectral application. In the case of biosensor application, the designed Penta-supercells-based biosensor and its ultra-high sensitivity of 2256 nm/RIU (4.5 times larger than the sensitivity of conventional plasmonic structures) can help the medical to detect low concentrations.

Simulation study of the space charge limit in heavy-ion synchrotrons

The SIS100 synchrotron as a part of the new Facility for Antiproton and Ion Research (FAIR) accelerator facility at GSI should be operated at the ``space charge limit'' for light- and heavy-ion beams. Beam losses due to space-charge-induced resonance crossing should not exceed a few percent during a full cycle. The recent advances in the performance of particle tracking tools with self-consistent solvers for the 3D space charge forces now allow us to reliably identify low-loss areas in tune space, considering the full SIS100 accumulation plateau of one second (160 000 turns) duration. A realistic magnet error model, extracted from precise bench measurements of the SIS100 main dipole and quadrupole magnets, is included in the simulations. Previously, such beam dynamics simulations required non-self-consistent space charge models. By comparing to the self-consistent simulations results, we are now able to demonstrate that the predictions from such faster space charge models can be used to identify low-loss regions with sufficient accuracy. The findings are applied by identifying a low-loss working point region in SIS100 for the design FAIR beam parameters. The bunch intensity at the space charge limit is determined. Several countermeasures to space charge are proposed to enlarge the low-loss area and to further increase the space charge limit.

The search of higher multipole radiation in gravitational waves from compact binary coalescences by a minimally-modelled pipeline

The coherent WaveBurst (cWB) pipeline implements a minimally-modelled search to find a coherent response in the network of gravitational wave detectors of the LIGO-Virgo Col-laboration in the time-frequency domain. In this manuscript, we provide a timely introduction to an extension of the cWB analysis to detect spectral features beyond the main quadrupolar emission of gravitational waves during the inspiral phase of compact binary coalescences; more detailed discussion will be provided in a forthcoming paper [1]. The search is performed by defining specific regions in the time-frequency map to extract the energy of harmonics of main quadrupole mode in the inspiral phase. This method has already been used in the GW190814 discovery paper (Astrophys. J. Lett. 896 L44). Here we show the procedure to detect the (3, 3) multipole in GW190814 within the cWB framework.

Preliminary 3D Mechanical Design of the FCC-hh Main Quadrupoles

For the Future Circular Collider hadron-hadron (FCC-hh), a 100 TeV post Large Hadron collider machine, 750 main quadrupoles with a 360 T/m gradient over a magnetic length of 7 m are required. They consist of a double aperture based on a laminated collar structure similar to the LHC MQ technology. In this paper, a preliminary 3D finite element analysis is performed to evaluate the stresses and strains of the complete magnet structure, with particular emphasis on maintaining coil pre-stress at the pole-coil interfaces under operation. Numerical results during preload, cool-down, and energization are presented in detail and discussed. The peak stress is of the order of 160 MPa in the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil with a localized gap of less than 6 μm at the coil-pole interface under nominal operation. The stress in the mechanical structure is bearable with only high stress values confined to very small areas.

FCC-hh Conceptual Designs and Windability of the Main Quadrupoles

In the framework of a design study for a post-LHC 100 TeV circular hadron collider, namely FCC-hh, high-gradient Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn lattice quadrupoles were investigated, following closely the specifications from the optic layout of that machine. After several iterations, a baseline design of the main quadrupole was selected and, then, included in the FCC-hh Conceptual Design Report. The article deals with the preliminary results of the 3-D electromagnetic and mechanical conceptual design. The 3-D design of Nb3Sn coil ends is known to be a critical phase, especially for small apertures. To tackle the potential issues, 3-D electromagnetic design was first carried out, taking into account the field quality constraints, the field margins in critical areas, and the windability of the coil ends. Then, winding trials with actual cables were performed, to help selecting designs and identifying critical geometrical parameters.

Lattice and optics options for possible energy upgrades of the Large Hadron Collider

Studies of possible energy upgrades of the Large Hadron Collider (LHC) aim at increasing the current nominal beam energy of 7 TeV in view of expanding the discovery potential and physics reach of the LHC. Some critical aspects of the feasibility of partial or full energy upgrades are studied here, together with novel mitigation measures. Higher beam energies can be realized by pushing the installed main dipoles to their limits or by replacing different fractions of installed magnets. Moreover, a revised lattice design for a full energy upgrade, also known as the high-energy LHC (HE-LHC), is presented. The studies reported focus on the linear optics design and on the lattice layout. In particular, an optics with 60\ifmmode^\circ\else\textdegree\fi{} transverse phase advance in the regular arc cells, meant to alleviate the strength requirements for the main quadrupoles, has been designed in view of possible beam tests during the next LHC run 3. The methods developed in this article, for matching the ring geometry to a reference tunnel, for improving the beam aperture, and for minimizing the required field strengths for new high-energy LHC-like machines, will also be applicable to other future circular collider projects.

An Improved Mutual Inductance Electromagnetic Model for Inductive Power Transfer Systems Under Misalignment Conditions

One of the most challenging components of an inductive power transfer system to be designed is the coil set (transmitter and receiver coils). Due to the great number of variables, finite element software is frequently used in the simulation of the electromagnetic quantities of coil sets. These simulations take a long time to produce results. To shorten the time it takes to design a coil set, different electromagnetic models have been published. However, the published models are still dependant on extensive equations that require several numerical loops to be solved, or are not completely validated. In this paper, a new compact electromagnetic model is proposed. The proposed model uses quadrupole superposition to predict the magnetic field, induced voltage, and inductances of a coil set through a cubic polynomial function, whose coefficients are based on the parameters of the coil set. With the proposed model, it is possible to compute the mutual inductance of multiple coil sets for different horizontal misalignment conditions, after simulating (or measuring) the open-circuit voltage of only one coil set at zero misalignment. Thus, the proposed model helps greatly for coil topology analysis and design. The proposed model is validated through seven different experimental set ups featuring different coil sets, including receivers and transmitters formed by multiple quadrupoles, a transmitter formed by one main quadrupole and a resonant booster, and coil sets working at 5 kHz and 85 kHz. The experimental results show an excellent agreement with the proposed model.

Cryogenic testing of fast ramping superconducting magnets for the SIS100 synchrotron

The international Facility for Antiproton and Ion Research FAIR is currently under construction at GSI, in Darmstadt, Germany. The core component of FAIR, the superconducting SIS100 synchrotron will operate with a high repetition rate of up to 1 Hz. The SIS100 ring with a circumference of 1083 m contains 108 main dipole magnets with a maximal field of 1.9 T. The ion-optical lattice of SIS100 contains also 166 main quadrupoles and 137 corrector magnets. The quadrupole and corrector magnets are assembled in the quadrupole units that are pair-wise integrated in quadrupole doublet modules. All superconducting magnets will be tested at liquid helium temperature to assure their compliancy with the specification. The main dipole modules are being tested at the magnet test facility at GSI. Cold testing of the quadrupole doublet modules is split in the testing of the quadrupole units at JINR, Russia and in testing of fully assembled quadrupole doublet modules at INFN, Italy. The cold testing program includes dynamic AC loss measurements and hydraulic adjustment of the parallel cooling channels of SIS100 next to the training, magnetic field measurements and other tests. We present the scope of cold testing of different types of magnet modules as well as the test results.

Performance of the Large Hadron Collider's Cryogenic Bypass Diodes Over the First Two Physics Runs, Future Projects, and Perspectives

Cryogenic bypass diodes have been installed in all superconducting dipole magnets (1232) and quadrupole magnets (392) of the Large Hadron Collider (LHC) at CERN, and operated during the physics runs since 2009. The bypass diodes are a fundamental ingredient of the quench protection system for those main dipoles and quadrupoles magnets. The diodes are located inside the magnet cryostats, operating in superfluid helium and exposed to ionizing radiation. The connection between the superconducting magnet and the bypass diode is made through a mechanical clamping system and copper bus bars. Since their first installation, all LHC diodes have undergone at least two full thermal cycles (from 1.9 K to room temperature and back to superfluid helium temperature). The evolution of electrical parameters as well as improvements and modifications made over a period of 10 years are reviewed in this paper. With CERN preparing for LHC's High Luminosity era, the long-term strategy for cold diodes is presented, based on the overall results and experience gathered so far, including the studies related to the tolerance with respect to the radiation doses and neutron fluences expected.

Improving high precision cam mover’s stiffness

Pre-alignment is a key challenge of the Compact Linear Collider (CLIC) study. The requirement for CLIC main beam quadrupole (MBQ) alignment is positioning to within 1 μm from target in 5 degrees of freedom (DOF) with ± 3mm travel. After motion, the position should be kept passively while the system's fundamental frequency is above 100Hz. Cam movers are considered for the task. Traditionally they are used for the alignment of heavier magnets with lower accuracy and stiffness requirement. This paper presents a new CLIC prototype cam mover with design emphasis on the fundamental frequency. A finite element method (FEM) model predicts the mode shapes and eigenfrequencies of the system and can be used for further improving the design. Experimental modal analysis (EMA) of the prototype shows that the prototype's fundamental frequency is at 44Hz. It also validates the FEM model.

Mössbauer studies of mixed-valence manganite Pb3(Mn0.965Fe0.035)7O15

Pb3Mn7O15 manganite with mixed valence (Mn3+/Mn4+) was studied by Mossbauer effect on 57Fe impurity atoms in the temperature range of 80–673 K. The experimental spectra consisted of two main quadrupole doublets corresponding to trivalent Fe atoms replacing Mn atoms in different positions in the crystal lattice. Identification of the doublets was made on the basis of calculations of quadrupole splitting within the point charges model and taking possible polarization of oxygen ions into account. In two temperature ranges: T ≈ 370–510 K, corresponding to the structural phase transition, and at T ≈ 140–230 K, where strong anomalies of the magnetic and electrical properties were observed, the sharp changes in the hyperfine quadrupole splitting were observed. It is assumed that these changes are caused by changes in the valence of manganese ions and structural deformations.

Exploration of Two Layer Nb3Sn Designs of the Future Circular Collider Main Quadrupoles

The goal of this study is to propose an alternative FCC quadrupole design where the risk from both their fabrication and their operation in the machine is reduced compared to previous analysis. Therefore, the number of coil layers has been reduced from four to two and the load-line margin has been increased from 14% to 20% compared to previous investigations (“Design of a Nb3Sn 400 T/m quadrupole for the future circular collider,” IEEE Trans. Appl. Supercond ., vol. 28, no. 3, p. 4004905, Apr. 2018). Indeed, the idea is to only challenge the ∼5000 FCC main dipoles and stay at a relatively low complexity for the ∼700 FCC main quadrupoles so they have a limiting impact on the machine operation and reliability. An exploration of the strand diameter (0.7–0.9 mm), the cable size (40–60 strands), as well as the protection delay (30–40 ms) is performed on two-dimensional (2-D) magnetic designs of the FCC main quadrupole. A discussion on cable windability allows for the selection of one design generating 367 T/m. The design is mechanically constrained with a conventional collar structure leading to collaring peak stress of 115 MPa. A single coupling-loss-induced quench unit ensures a safe magnet operation with a 300 K hotspot temperature.

Stability modeling of the LHC Nb-Ti Rutherford cables subjected to beam losses

The Large Hadron Collider (LHC) at CERN is being prepared for its full energy exploitation during run III, i.e., an increase of the beam energy beyond the present 6.5 TeV, targeting the maximum discovery potential attainable. This requires an increase of the operating field of the superconducting dipole and quadrupole magnets, which in turn will result in more demanding working conditions due to a reduction of the operating margin while the energy deposited by particle loss will increase. Beam-induced magnet quenches, i.e., the transition to normal conducting state, will become an increasing concern, because they could affect the availability of the LHC. It is hence very important to understand and be able to predict the quench levels of the main LHC magnets for the required values of current and generated magnetic fields. This information will be used to set accurate operating limits of beam loss, with sufficient but not excessive margin, so to achieve maximal beam delivery to the experiments. In this study we used a one-dimensional, multistrand thermal-electric model to analyze the maximum beam losses that can be sustained by the LHC magnets, still remaining superconducting. The heat deposition distribution due to the beam losses is given as an input for the stability analysis. Critical elements of the model are the ability to capture heat and current distribution among strands, and heat transfer to the superfluid helium bath. The computational model has been benchmarked against energy densities reconstructed from beam-induced main dipole quenches during LHC operation at 6.5 TeV. The model was then used to evaluate the stability margin of both main dipole and main quadrupole magnets at different beam energies, up to the expected ultimate operating energy of the LHC, 7.5 TeV. The comparison between the quench levels underlines how the increase of beam energy implies a substantial reduction of magnets stability and will require much stricter setting on the allowable beam losses to avoid resistive transitions during operation.

On the importance of magnetic material characterization for the design of particle accelerator magnets

In this paper, the importance of magnetic material measurements in the framework of the design of magnets for particle accelerator is discussed. In particular, five samples of different ferromagnetic materials are analyzed experimentally and compared with literature results. These materials have been (or will be) used for producing yokes for several normal-conductor magnets at CERN, such as REX-ISOLDE main dipole, ELENA dipole and quadrupole, and SESAME dipole. The comparison with literature shows several disagreements. The main one of them is analyzed in detail in a case study based on finite elements simulation of a quadrupole magnet installed in CERN. This analysis shows that a good knowledge of the yoke initial magnetization curve is important to guarantee a given level of magnet performance, especially concerning its field quality.

Design and Construction of the Magnet Cryostats for the SuperKEKB Interaction Region

The beam final focus system in the SuperKEKB interaction region consists of 55 superconducting magnets including eight main quadrupole magnets. Two cryostats for these magnets were required to be operated inside the Belle-II particle detector because of the magnet positions by the SuperKEKB beam optics. The cryostats were designed under constraints of the space and the electromagnetic forces with Belle-II. Construction of the cryostats was completed, and they were installed into the SuperKEKB interaction region. Cold tests of the cryostats were performed, and all magnets were successfully excited at the operation currents. In this paper, the design and the construction of the cryostats are presented.

Design of a Nb3Sn 400 T/m Quadrupole for the Future Circular Collider

For the Future Circular Collider (FCC), a 100-TeV post Large Hadron Collider machine, 750 main quadrupoles with a gradient of around 400 T/m are required. This paper presents an electromagnetic design optimization of a double aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole, fulfilling the specifications and a structural design of a single aperture configuration towards a prototype.

Development and validation of a multilateration test bench for particle accelerator pre-alignment

The development and validation of a portable coordinate measurement solution for fiducialization of compact linear collider (CLIC) components is presented. This new solution addresses two limitations of high-accuracy state-of-the-art coordinate measuring machines, i.e. lack of portability and limited measurement volume. The solution is based on frequency scanning interferometry (FSI) distances and the multilateration coordinate measurement technique. The developments include a reference sphere for localizing the FSI optical fiber tip and a kinematic mount for repositioning the reference sphere with sub-micrometric repeatability. This design enables absolute distance measurements in different directions from the same point, which is essential for multilateration. A multilateration test bench built using these prototypes has been used to fiducialize a CLIC cavity beam position monitor and 420 mm-long main beam quadrupole magnet. The combined fiducialization uncertainty achieved is 3.5 μm (k = 1), which is better than the CLIC 5 μm (k = 1) uncertainty specification.

Quench Level of the HL-LHC Nb3Sn IR Quadrupoles

The scope of the Large Hadron Collider Hi-Lumi Project at CERN includes the installation of several superconducting magnets wound with Nb 3 Sn Rutherford cables. The quench level of these magnets (i.e. the maximum energy that a cable can tolerate without quenching) is a key value required to set magnet protection from beam losses, and is expected to be significantly different from the computed and measured levels of the LHC NbTi magnets. In this work, we applied a one-dimensional numerical model of multi-strand Rutherford cables to simulate the electro-thermal instabilities caused by the heat released by the particle beam losses. Two models have been applied, one based on the analysis of the single strand, and the other accounting for all the strands in the multi-strand cable. The results of these two models are compared to analyze the effects of heat and current redistribution during quench. A comparison between the quench energy values obtained for the Nb 3 Sn conductor in the working conditions of the LHC Hi-Lumi inner triplet low-β quadrupole (MQXF) and those of the NbTi Rutherford cable of the LHC main quadrupole magnet (MQ) is presented.

Conductor Specification and Validation for High-Luminosity LHC Quadrupole Magnets

Author(s): Cooley, LD; Ghosh, AK; Dietderich, DR; Pong, I | Abstract: The high-luminosity upgrade of the large hadron collider (HL-LHC) at CERN will replace the main ring inner triplet quadrupoles, identified by the acronym MQXF, adjacent to the main ring intersection regions. For the past decade, the U.S. LHC Accelerator RaD Program, LARP, has been evaluating conductors for the MQXFA prototypes, which are the outer magnets of the triplet. Recently, the requirements for MQXF magnets and cables have been published in [P. Ferracin et al., IEEE Trans. Appl. Supercond., vol. 26, no. 4, Jun. 2016, Art. no. 4000207], along with the final specification for Ti-alloyed Nb3Sn conductor determined jointly by CERN and LARP. This paper describes the rationale beneath the 0.85-mm-diameter strand's chief parameters, which are 108 or more subelements, a copper fraction not less than 52.4%, strand critical current at 4.22 K not less than 631 A at 12 T and 331 A at 15 T, and residual resistance ratio of not less than 150. This paper also compares the performance for ∼100 km production lots of the five most recent LARP conductors to the first 163 km of strand made according to theHL-LHCspecification.Two factors emerge as significant for optimizing performance and minimizing risk: a modest increase of the subelement diameter from 50 to 55 μm, and a Nb:Sn molar ratio of 3.6 instead of 3.4. The statistics acquired so far give confidence that the present conductor can balance competing demands in production for the HL-LHC project.