Stress management as an enabling technology for high-field superconducting dipole magnets

Abstract

This dissertation examines stress management and other construction techniques as means to meet future accelerator requirement demands by planning, fabricating, and analyzing a high-field, Nb₃Sn dipole. In order to enable future fundamental research and discovery in high energy accelerator physics, bending magnets must access the highest fields possible. Stress management is a novel, propitious path to attain higher fields and preserve the maximum current capacity of advanced superconductors by managing the Lorentz stress so that strain induced current degradation is mitigated.

Stress management is accomplished through several innovative design features. A block-coil geometry enables an Inconel pier and beam matrix to be incorporated in the windings for Lorentz Stress support and reduced AC loss. A laminar spring between windings and mica paper surrounding each winding inhibit any stress transferral through the support structure and has been simulated with ALGOR^®. Wood's metal filled, stainless steel bladders apply isostatic, surface-conforming preload to the pier and beam support structure. Sufficient preload along with mica paper sheer release reduces magnet training by inhibiting stick-slip motion. The effectiveness of stress management is tested with high-precision capacitive stress transducers and strain gauges.

In addition to stress management, there are several technologies developed to assist in the successful construction of a high-field dipole. Quench protection has been designed and simulated along with full 3D magnetic simulation with OPERA^®. Rutherford cable was constructed, and cable thermal expansion data was analysed after heat treatment. Pre-impregnation analysis techniques were developed due to elemental tin leakage in varying quantities during heat treatment from each coil. Robust splicing techniques were developed with measured resistivites consistent with nΩ joints.

Stress management has not been incorporated by any other high field dipole research laboratory and has not yet been put to a definitive high-field test. The TAMU Physics Accelerator Research Laboratory has constructed a Nb ₃Sn dipole, TAMU3, that is specially designed to provide a test bed for high-field stress management.