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, 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.

Analysis of a Novel Toroidal Configuration for Hadron Therapy Gantries

Enrico Felcini

Hadron therapy refers to a medical treatment that uses hadron beams (i.e. protons and ions) to deliver localized energy that suppresses cancerous cells, sparing the neighbouring healthy tissues from unwanted radiation. The major technical components of a hadron therapy centre are the particle accelerator (cyclotron, synchrotron, or linac) and the beam delivery system that controls, shapes and orients the particles towards the area to be treated. The beam delivery can consist of fixed transfer lines, or it can include a gantry, a transfer line that rotates around the patient and allows radiation from multiple directions. The present work investigates a new toroidal gantry for hadron therapy, named GaToroid. This novel gantry configuration allows the dose delivery from a discrete number of angles avoiding magnets as well as patient rotation. Compared to traditional gantries that require rotating magnets, this improvement is made possible by a toroidal magnet operating in steady-state. This design constitutes the ideal conditions for the use of superconductors to generate a significantly higher magnetic field compared to normal-conducting solutions, as well as to reduce the weight and footprint of the magnets. The study of a GaToroid system requires the integration of several aspects of physics and engineering. In this framework, the focus of this research is on the design of the superconducting coils integrated with beam optics and particle tracking analyses. The first part of the thesis illustrates the optimization of the toroidal magnet. Coupling two-dimensional particle tracking and magnetic field calculations, an algorithm was developed to identify optimal gantry configurations that maximize the energy acceptance of the system. Two solutions composed of 16 coils, differing in high and low values of engineering current density, were investigated. In line with current clinical requirements, the beams converged at the isocenter within 1 mm over the whole treatment energy spectrum for both configurations. The second part of the thesis describes the algorithm implemented for the two- and three-dimensional particle tracking. Building upon the results of the magnetic optimization, a linear beam optics formalism was developed to determine the focusing properties of GaToroid. The third part of the thesis focuses on the engineering design of the low current density solution. Using two thermo-electric models, lumped and one-dimensional, the Nb-Ti and ReBCO cable geometries were validated, together with the quench protection system. Furthermore, analytical and numerical studies on mechanics made it possible to estimate the overall footprint and weight of the system. Results show that, compared with the state-of-the-art gantries, the proposed GaToroid solution has the potential to be more compact and lighter by at least a factor two. Finally, the last part of the thesis describes the design of a scaled-down demonstrator wound with ReBCO tapes. Studies on quench protection, mechanics and experimental implementation aimed at testing the use of ReBCO technology for GaToroid coils are discussed. In conclusion, this work presents the first overall description of a GaToroid system, ranging from the analytical definition, magnetic optimization, particle tracking and magnet engineering. The investigation of this new toroidal paradigm for gantries represents a quantum step toward more compact and less expensive solutions for hadron therapy centres.

EPFL2021

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

Luca Bottura, Enrico Felcini, Pier Paolo Granieri

The full energy exploitation of the Large Hadron Collider (LHC), a planned increase of the beam energy beyond the present 6.5 TeV, will result in more demanding working conditions for the superconducting dipoles and quadrupoles operating in the machine. It is hence crucial to analyze, understand, and predict the quench levels of these magnets for the required values of current and generated magnetic fields. A one-dimensional multi-strand electro-thermal model has been developed to analyze the effect of beam-losses heat deposition. 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 experimental values of LHC quench limits measured at 6.5 TeV for the Main Bending dipole magnets.

2019

Investigations of Quench Limits of the LHC Superconducting Magnets

Bernd Dehning, Agnieszka Priebe, Minh Quang Tran

NbTi-based Rutherford cables are used in the coils of the Large Hadron Collider (LHC) magnets. These cables are designed to operate with currents up to 13 kA at temperatures of 1.9 K. Beam losses can locally heat the superconducting cables above the critical temperature and cause a transition to the normal conducting state (quenching). The quench limit, i.e., the energy needed for this transition, is studied to determine the maximum beam intensities and luminosity reach of the LHC. The amount of energy deposited in the coil cannot be measured directly. Therefore, Geant4 simulations are used to correlate the deposited energy with the signal from secondary particles detected outside the magnet cryostat by ionization chambers. An orbital bump technique is used to induce controlled beam losses and provoke a quench. The energy deposition is analyzed in terms of various beam loss patterns and beam energies. The validation of the heat transfer code is presented. The development of the resistive zone is estimated and compared with the voltage measurements over the coils.

Ieee-Inst Electrical Electronics Engineers Inc2013

Analysis of a Novel Toroidal Configuration for Hadron Therapy Gantries

Enrico Felcini

EPFL2021