Vol. 34 - Optimization of quench protection heater performance in high-field accelerator magnets through computational and experimental analysis

Superconducting accelerator magnets with increasingly hi gh magnetic fields are being designed to improve the performance of the Large Hadron Collider (LHC) at CERN. One of the technical challenges is the magnet quench p rotection, i.e., preventing damage in the case of an unexpected loss of superc onductivity and the heat generation related to that. Traditionally this is d one by disconnecting the magnet current supply and using so-called protection he aters. The heaters suppress the superconducting state across a large fraction of the winding thus leading to a uniform dissipation of the stored energy. Preli minary studies suggested that the high-field Nb 3 Sn magnets under development for the LHC luminosity upgrade (HiLumi) could not be reliably protected using the existing heaters. In this thesis work I analyzed in detail the present state-of-the-art protection heater technology, aiming to optimize its perfo rmance and evaluate the prospects in high-field magnet protection. The heater efficiency analyses focused on the time delays from heater acti- vation to normal zone initiation in the coils. I developed a n umerical simulation tool CoHDA (Code for Heater Delay Analysis) to model the heat tra nsfer from the heater to the cables and estimate the delay based on the su perconductor critical surface. All the important parameters relative to t he heater, the cable, and the magnet operation conditions were included. The simu lation results were validated experimentally using measured data from sev eral R&D Nb 3 Sn quadrupoles and dipoles. Then, a method based on parametric sweeps was utilized to optimize the heater layouts. The goal was to mini mize the delay to quench the entire coil, taking into account the different fi eld regions. New heater designs were proposed for the Nb 3 Sn R&D prototype LHQ and the HiLumi quadrupole QXF. Finally, I simulated the heaters in hig h tempera- ture superconductor magnets, which are being considered fo r the LHC energy upgrade. Consequently, I proposed technology improvement s to increase the heater energy in order to meet the requirements also in these very high-field magnets.