Stress Management as an Enabling Technology for High-Field Superconducting Dipole Magnets

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, Nb_(3)Sn 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_(3)Sn dipole, TAMU3, that is specially designed to provide a test bed for high-field stress management

Simulation results of an inductively-coupled rf plasma torch in two and three dimensions for producing a metal matrix composite for nuclear fuel cladding

I propose to develop a new method for the synthesis of metal matrix composites (MMC) using aerosol reactants in a radio frequency (RF) plasma torch. An inductivelycoupled RF plasma torch (ICPT) may potentially be designed to maintain laminar flow and a radial temperature distribution. These two properties provide a method by which a succession of metal layers can be applied to the surface of SiC fibers. In particular, the envisaged method provides a means to fully bond any desired metal to the surface of the SiC fibers, opening the possibility for MMCs in which the matrix metal is a highstrength steel. A crucial first step in creating the MMC is to test the feasibility of constructing an ICPT with completely laminar flow in the plasma region. In this work, a magnetohydrodynamic (MHD) model is used along with a computational fluid dynamic (CFD) software package called FLUENT© to simulate an ICPT. To solve the electromagnetic equations and incorporate forces and resistive heating, several userdefined functions (UDF) were written to add to the functionality of FLUENT©. Initially, an azimuthally-symmetric, two-dimensional model was created to set a test baseline for operating in FLUENT© and to verify the UDF. To incorporate coil angle and current leads, a fully three dimensional model UDF was written. Preliminary results confirm the functionality of the code. Additionally, the results reveal a non-mixing, laminar flow outer region for an axis-symmetric ICPT

Two-Layer 16 Tesla Cosθ Dipole Design for the FCC

The Future Circular Collider or FCC is a study aimed at exploring the possibility to reach 100 TeV total collision energy which would require 16 tesla dipoles. Upon the conclusion of the High Luminosity Upgrade, the US LHC Accelerator Upgrade Pro-ject in collaboration with CERN will have extensive Nb3Sn magnet fabrication experience. This experience includes robust Nb3Sn conductor and insulation scheming, 2-layer cos2θ coil fabrication, and bladder-and-key structure and assembly. By making im-provements and modification to existing technology the feasibility of a two-layer 16 tesla dipole is investigated. Preliminary designs indicate that fields up to 16.6 tesla are feasible with conductor grading while satisfying the HE-LHC and FCC specifications. Key challenges include accommodating high-aspect ratio conductor, narrow wedge design, Nb3Sn conductor grading, and especially quench protection of a 16 tesla device

Analysis of Field Errors for LARP Nb3_3 Sn HQ03 Quadrupole Magnet

The U.S. large hadron collider (LHC) Accelerator Research Program, in close collaboration with The European Organization for Nuclear Research (CERN), has developed three generations of high-gradient quadrupole (HQ) Nb3Sn model magnets, to support the development of the 150 mm aperture Nb3Sn quadrupole magnets for the high-luminosity LHC. The latest generation, HQ03, featured coils with better uniformity of coil dimensions and properties than the earlier generations. The HQ03 magnet was tested at fermi national accelerator laboratory (FNAL), including the field quality study. The profiles of low-order harmonics along the magnet aperture observed at 15 kA, 1.9 K can be traced back to the assembled coil pack before the magnet assembly. Based on the measured harmonics in the magnet center region, the coil block positioning tolerance was analyzed and compared with earlier HQ01 and HQ02 magnets to correlate with coil and magnet fabrication. To study the capability of correcting the low-order nonallowed field errors, magnetic shims were installed in HQ03. The expected shim contribution agreed well with the calculation. For the persistent-current effect, the measured a4 can be related to 4% higher in the strand magnetization of one coil with respect to the other three coils. Finally, we compare the field errors due to the interstrand coupling currents between HQ03 and HQ02

Geometric field errors of short models for MQXF, the Nb3_{3}Sn low-β\beta quadrupole for the High Luminosity LHC

In the framework of the high-luminosity upgrade of the large hadron collider, the U.S. LARP collaboration and CERN are jointly developing a 150-mm aperture Nb$_{3}$Sn quadrupole for the Large Hadron Collider (LHC) interaction regions. Due to the large beam size and orbit displacement in the final focusing triplet, MQXF has challenging targets for field quality at nominal operation conditions. Three short model magnets have been tested and around 30 coils have been built, allowing a first analysis of the reproducibility of the coil size and turns positioning. The impact of the coil shimming on field quality is evaluated, with special emphasis on the warm magnetic measurements and the correlation to field measurements at cold and nominal field. The variability of the field harmonics along the magnet axis is studied by means of a Monte-Carlo analysis and the effects of the corrective actions implemented to suppress the low-order unallowed multipoles are discussed