Analysis of Quench Detection and Protection of a Nb3Sn CCT Technology Demonstrator Dipole for FCC

From 2016, Paul Scherrer Institut (PSI) started an activity related to developing design, construction and testing of the superconducting magnets. My thesis work is part of this activity and mainly concerns the design and construction of an innovative high-field superconducting magnet of the Canted-Cosine-Theta (CCT) type - a possible candidate for the Future Circular Collider (FCC) 16 T dipole magnet design. The unique mechanical structure intercepts the accumulated forces lowering the stress on the windings, constituting intrinsic stress management in the high-field Nb3Sn accelerator magnets. However, this structure also constitutes a barrier for heat to quickly propagate in case of a quench. To succeed in the CCT-type magnet design and construction, quench protection is a challenging task that requires a detailed investigation of the electrothermal behavior of this magnet. In this thesis, the potential detection and protection concepts are studied by the multiphysics simulations on a two-layer short model built at PSI and also in a subscale experiment. The 2D User-Defined Elements (UDEs) developed at Lawrence Berkeley National Laboratory (LBNL) in ANSYS Mechanical APDL, which support multi-dependence material properties and include the effect of inter-filament coupling currents, are adapted and used in the coupled electrothermal, electrodynamic, and electrical-circuits calculations for a two-layer CCT-type magnet with different protection methods, such as Coupling-Loss Induced Quench (CLIQ) and Energy-Extraction (EE) system. A first-of-a-kind CCT-type magnet protection study using UDEs is presented. The generic model method is validated through the test data of CCT4, a model magnet constructed at LBNL, protected by an energy-extraction system. The simulation predictions are the first steps of the conceptual design and feasibility validation of the construction of a fast and efficient quench protection system for CCT-type magnets to be operated in an accelerator. These calculations are to be compared to the experimental data in the near future on the PSI's first 1-m long two-layer CCT-type model magnet, CD1. Furthermore, these studies lay the ground for the four-layer CCT protection concepts for FCC.

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

Luca Bottura, Enrico Felcini

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, multi-strand 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 MB (Main Bending) dipole quenches during LHC operation at 6.5 TeV. The model was then used to evaluate the stability margin of both MB and MQ (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.

2019

Quench Level of the HL-LHC Nb3Sn IR Quadrupoles

Luca Bottura, Enrico Felcini

The scope of the Large Hadron Collider Hi-Lumi Project at CERN includes the installation of several superconducting magnets wound with Nb3Sn 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 Nb-Ti 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 Nb3Sn 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. The differences and similarities in quench performance between the impregnated cables for Nb3Sn magnets and the non-impregnated ones for NbTi magnets at their respective typical working conditions in superconducting accelerator magnets are highlighted.

2017

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

Luca Bottura, Enrico Felcini

2019