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

Abstract

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.

Modeling of Beam Loss Induced Quenches in the LHC Main Dipole Magnets

“…The model was benchmarked against experimental values of the LHC quench limits reconstructed from the machine operation quenches at 6.5 TeV of beam energy for the MB (Main Bending) dipole magnets [38]. The model was able to reproduce the experimental results over a wide range of heat deposition times (as shown in Section IV.B), and was therefore applied to compare different beam energies and to the analysis of the LHC Main Quadrupole [41].…”

“…Fig. 7 also reports quench and no-quench energy data points reconstructed from the LHC machine operation in the three years from 2016 to 2018, as explained in detail in [41].…”

Study of dust-induced beam losses in the cryogenic arcs of the CERN Large Hadron Collider

“…Comparing the distributions for the two upper intensity intervals, the characteristics of dust particle events are not expected to get significantly worse in the HL-LHC era. The minimum energy deposition density for inducing a quench decreases for shorter heating times, but this decrease is small for τ < 10 −4 s [48,51]. The shift of the τ distribution is therefore not expected to considerably increase the risk of quenches.…”

“Mirror” magnet experiment for quench studies, quench analysis techniques development and in support of superconducting magnet modeling

“…Results are not directly linked or linkable to quench sources though. On a small time-scale which is more relevant for fundamental research, detailed models provide a good basis for process description, even on a grand magnet scale [4], [11], [33]. While available software proves to be invaluable for magnet design and performance analysis, we still need to try distinguishing quench cases where multi-physics software can be tested in more complex conditions.…”

“…It also takes place during quenching and can serve as an indicator of it and possibly as a precursor of it. While the physics of current redistribution is clear and various related processes studied [4[, [5], [12], [32], [33], [34] a significant complication for interpretation in real magnets is the existence of splices (review on splice/joint technology for various superconductors can be found in [35]). Lead splices can be considered in approximation of equal potential for all strands or equal current in all strands with the two giving very different current/power loss distribution outcomes [4].…”