Magnetics Business & Technology - Fall 2011 - (Page 6)

FEATURE ARTICLE By Chris riley, TeChnology Manager • VeCTor Fields soFTware, CoBhaM TeChniCal serViCes Integrated Design Tools for Low and High Temperature Superconducting Magnets Superconducting magnets and magnetic systems are making an impact all over the world. Magnetic resonance imaging (MRI) has become the main medical diagnostic visualization tool for soft tissue, and we have all become used to seeing detailed scans of sections through the human brain and other vital organs and joints. The only realistic technology for whole body scanners, which require a highly homogeneous field region of 2 Tesla or more in a 0.5 m diameter sphere, is superconducting magnets. The same technology is also used for nuclear magnetic resonance (NMR) systems which make extensive use of superconducting magnets to achieve much higher fields, albeit with a smaller homogeneous region, for material analysis. Keeping particles on track as they approach the speed of light in the Large Hadron Collider and other particle accelerators can only be attained using very powerful superconducting magnets. The advent of high temperature superconductors (HTS) has also reinvigorated the interest in superconducting windings to replace lossy copper ones in synchronous motors and generators, with the added bonus that substantial physical size reduction can be achieved for a particular power rating. However, superconducting materials are still relatively expensive and “right first time” is an important paradigm. Software design and simulation tools play a vital role in achieving this. In particular, the simulation of superconducting quench (the transition from the superconducting to the normal state) is a critical part of the design process. Superconducting magnets must be designed to withstand quenches, whether these are anticipated, such as occur during training due to micro movements of the windings, or from unexpected events such as earth tremors. Failure to withstand quench can be catastrophic with considerable mechanical damage to the magnet and cryogenics. Safe dissipation of the very large stored energy in the magnet following a quench requires sophisticated protection circuitry to also be an integral part of the magnet design. Magnet energies are increasing all the time, with HTS inserts extending the range of field that can be achieved beyond the limits for low temperature superconductor (LTS) magnets, because HTS is able to operate at higher field intensity. Accurate characterization of HTS and LTS materials at temperatures approaching absolute zero is also vital for quench simulation. Material properties can change by an order of magnitude within a few degrees at low temperatures and magneto-resistive effects also become more prominent. Consequently, electromagnetic, circuit, thermal and mechanical behavior must all be addressed simultaneously; a true multi-physics challenge. To improve the capability of design tools for this demanding application, the UK Technology Strategy Board (under program TP/5/MAT/6/I/H0647B) has supported a collaboration between three of the UK’s leading groups. The project, entitled “Integrated Modelling Package for Designing Advanced HTS Materials Applications (IMPDAHMA)”, was led by Oxford Instruments Nanoscience (OINS), who design and manufacture magnets, in Figure 1. Temperature distribution 0.1 seconds after quench initiation Figure 2. Effect of discretization and element type on accuracy Figure 3. Mosaic mesh with hexahedral, tetrahedral and pyramid elements 6 Magnetics Business & Technology • Fall 2011 www.MagneticsMagazine.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Fall 2011

Magnetics Business & Technology - Fall 2011
Table of Contents
Editor’s Choice
Integrated Design Tools for Low and High Temperature Superconducting Magnets
Special Report: Magnetics for Wind Power Technology
Research & Development
Magnets • Materials • Measurement
Application • Component Developments
Industry News
Marketplace
Calendar of Events
Advertising Index
Spontaneous Thoughts: Sputnik Moment: Revisited

Magnetics Business & Technology - Fall 2011