Future circular particle accelerators with collision energies significantly beyond the LHC will require magnets with higher magnetic field. Quench protection of such magnets is challenging for two ...main reasons. First, the high energy density and relatively high margin to quench require a high-performance quench protection system. Second, integration of the protection system in an accelerator machine foreseen to be operated for decades calls for easy-to-integrate, robust, and redundant elements. A new and promising protection method named Secondary CLIQ (S-CLIQ) has recently been proposed. It relies on auxiliary normal-conducting coils that are electrically insulated from the coils to protect but are magnetically coupled to them. Upon magnet quench detection, the coupled coils have dual functionality: first, they introduce high coupling loss in the superconductor, which is sufficient to transfer most of the windings to the normal state in a few milliseconds; second, they extract part of the magnet's stored energy by magnetic coupling. In this work, a S-CLIQ system based on auxiliary coils placed on the top and bottom of a racetrack magnet and made of a thin 1 mm<inline-formula><tex-math notation="LaTeX">^{2}</tex-math></inline-formula> wire is presented. It is shown that the quench protection performance in terms of hot-spot temperature and peak voltage to ground are superior to alternative methods such as energy extraction, quench heaters, and CLIQ.
Secondary CLIQ is a quench protection method for protecting high-field accelerator magnets that involves charged capacitors into secondary normal-conducting coils that are magnetically coupled to the ...superconducting coils. The resulting coupling losses quickly brings the magnet to normal state and safely discharges it. No direct electrical or thermal link is required between the primary and secondary coils, and robust insulation is placed in between them. The two secondary circuits per magnet are galvanically insulated from the primary circuit, so that the tens to hundreds of CLIQ units needed to protect an accelerator circuit are galvanically insulated from one-another and from the superconducting magnets. The two secondary circuits per magnet each feature a CLIQ unit, and each CLIQ unit discharge is sufficient to bring the magnet to normal state over the entire operational current range. The coil geometry is such that the CLIQ discharge does not raise the voltage over the half-turns of the superconducting coils. After the superconducting coils develop resistance, a significant fraction of the stored magnetic energy is inductively transferred to and dissipated in the secondary coils. The resulting favourable adiabatic hot-spot temperature and voltage-to-ground enables the magnet designer to reduce the copper content of the superconducting coils, and thus lower the overall cost of the magnet. Secondary CLIQ quench simulations were performed on a hypothetical 14 m variant of the HD2 Nb3Sn dipole with a bore field of 16 T. It is demonstrated that the Secondary CLIQ method protects the magnet over its entire operational current range even in the case where one of the two CLIQ units fails to discharge with an adiabatic hotspot temperature of 248 K and voltage-to-ground of 610 V under nominal protection conditions, and a worst-case adiabatic hot-spot temperature of 263 K and voltage-to-ground of 840 V under fault conditions.
Curved superconducting bending magnets have clear potential for compact hadron therapy gantries and medical synchrotrons. A combined function superconducting bending magnet design based on collared ...cos-theta coils is proposed for a new compact and cost-effective hadron therapy gantry initiative. This 3 T magnet, based on the technologies extensively developed for the LHC project, includes several gantry-specific features that shall be developed and validated with a demonstrator magnet. The main development areas include fabrication of epoxy-impregnated cos-theta Nb-Ti coils with 2.2 m radius of curvature along with the assembly of the surrounding curved cold mass. This paper presents the magnetic and mechanical design optimization of the proposed demonstrator magnet, the results of the numerical modelling of the transient losses during operation as well as the magnet quench protection analysis.
The quench process in a superconducting magnet is inherently transient and three-dimensional (3D). In many cases, such as magnets protected by active protection systems, this transient can be ...accurately simulated with a two-dimensional model. However, a more complex 3D model is required in the case of a self-protected magnet. Simulations are particularly challenging due to physical and geometrical features, such as highly non-linear material properties, sudden appearance of localized heat generation, non-isotropic conductors, and relatively thin insulation layers. In this work, it is shown how the quench and heat diffusion in 3D geometry can be accurately yet rapidly simulated using the finite-difference method. The coupled electro-thermal problem is solved with a semi-implicit Euler method. This 3D approach is included as a new feature in the STEAM-LEDET quench simulation software. As a study case, a simulation of the transient following a quench occurring in one of the self-protected LHC magnets is presented. Simulation results are found in excellent agreement with experimental results. The influence of 2D and 3D geometry, inter-filament coupling loss, and quench location on the simulated transient is discussed.
Abstract
Small orbit oscillations of the circulating particle beams have been observed immediately following quenches in the LHC’s superconducting main dipole magnets. Magnetic fields generated ...during the discharge into the quench heaters were identified as the cause. Since the resulting, shielded field inside the beam screen cannot be measured in-situ, the time evolution of the field has to be reconstructed from the measured beam excursions.
In this paper, the field-reconstruction method using rotation in normalized phase space and the optimized fitting algorithm are described. The resulting rise times and magnetic field levels are presented for quench events that occurred during regular operation as well as for dedicated beam experiments. Finally, different approaches to model the shielding behavior of the beam screen are discussed.
To meet the milestones set by the High-Luminosity LHC (HL-LHC) project, the integration of new inner triplet magnet circuits is vital for enhancing the focusing of the particle beams at ATLAS and ...CMS. In addition to the Nb 3 Sn quadrupole magnets, high-order Nb-Ti magnets are required for field correction. This comprises self-protected magnets with six, eight, ten, and twelve poles, which also come in skewed variants. The simulation program LEDET was developed as part of the STEAM framework and is now applied to study quench transients in HL-LHC magnets. The electromagnetic and thermal transients occurring after a quench are simulated and validated with experiments at different current levels conducted by LASA (INFN). For the models, the three-dimensional geometry is accurately replicated and for each magnet the conductor parameters of each coil are set according to measurements. After discussing the various assumptions of the model, a simulation study is conducted to investigate the influence of the unknown quench location and inter-filament coupling losses. The developed models of each magnet show satisfactory accuracy and are predictive for different current levels. The models are then used to analyse the simulated hot-spot temperatures and peak voltages-to-ground, which cannot be easily measured. It is concluded that the protection strategy is effective.
A large aperture dipole magnet for testing inserts and cables at high field is under development at LBNL. Its design targets a 15 T field in a 144 mm by 94 mm rectangular aperture, and is based on ...block coils with flared ends. The coils are inserted in an aluminum shell based structure and prestressed using the bladder and key technology. The quench protection relies on energy extraction. Measurements and computations on cos(<inline-formula><tex-math notation="LaTeX">\theta</tex-math></inline-formula>) magnets have shown that the temperature rise after quench events and its gradient within the windings can significantly increase the mechanical stresses in the superconducting coils. In this study, we couple STEAM-LEDET 2-dimensional (2D) quench simulations to the 2D electro-thermo-mechanical ANSYS model of the magnet, predicting the stress acting on the coils during a quench discharge after activating the energy extraction system. The model is then used to optimize the quench protection system, in terms of hot-spot temperature, peak voltage, and limiting the peak stress reached during an energy discharge below the cooldown and powering one.
The Fusillo project at CERN aims to design and build a demonstrator magnet with multi-harmonic corrected fields in a 90° curved CCT magnet. In the first stage, a subscale magnet is built with 30° ...bending, about 1/30 of the demonstrator conductor length, and increased current to reach coil stresses equivalent to the demonstrator. The subscale magnet enables qualification of the technology developments, fabrication methods, winding and assembly procedures, and magnetic and quench protection design and measurement setups. The subscale magnet comprises two tilted solenoids with an opposite inclination on curved aluminium formers. Each solenoid has two channel turns with 70 Nb-Ti/Cu wires. The magnet is protected by an active quench detection with energy extraction (EE). EE causes current decay, which induces eddy currents in the formers. As a result, the differential inductance of the magnet is reduced, and the formers heat up, with the potential to strongly influence the quench behaviour of the windings. Calculation of the eddy currents and heat propagation in the formers with simultaneous quench propagation in the magnet windings requires a three-dimensional (3D) simulation. A cooperative simulation approach has been developed to simulate transients in this magnet. It involves two software tools developed at CERN as part of the STEAM framework: a finite element-based tool called FiQuS and a finite difference-based tool called LEDET. FiQuS calculates eddy currents in the formers and the temperature of the formers, whereas LEDET calculates windings' temperature, current and voltage. This approach enables a 3D quench simulation with great geometrical detail while maintaining reasonable computational cost. The simulation results are compared to measurement results from the forced EE. The agreement between the measurements and simulations is presented, and the key factors that affect magnet quench behaviour are identified.
Measuring the complex impedance of a superconducting magnet as a function of frequency provides valuable insight into its electrodynamics. In particular, the characteristic features of some ...non-conform behaviour, such as an insulation fault, may be easier to assess when performing impedance measurements rather than observing time-domain signals. A physics-driven equivalent circuit model of a superconducting magnet has been recently developed, whose parameters are derived using solely measured geometric and material properties. This contribution describes its validation against impedance measurements of a spare LHC superconducting main dipole, performed at the CERN magnet test facility. The proposed model includes lumped-elements capturing individual physical phenomena, such as superconducting filament magnetization, inter-filament and inter-strand coupling currents, eddy currents in the strand copper matrix and various magnet components, and stray capacitances. It is possible to predict the impact of different physical effects in different frequency ranges and compare simulations to experimental results. It is shown that the validated model can accurately reproduce the magnet's impedance in a frequency range up to 5 kHz in the different conditions considered.
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